INJURIES IN CRICKET: EPIDEMIOLOGY AND FACTORS ASSOCIATED WITH LUMBAR SPINE INJURY IN CRICKET FAST BOWLERS. Alex Kountouris

Transcription

1 INJURIES IN CRICKET: EPIDEMIOLOGY AND FACTORS ASSOCIATED WITH LUMBAR SPINE INJURY IN CRICKET FAST BOWLERS Alex Kountouris Bachelor of Applied Science (Physiotherapy), La Trobe University. Post Graduate Diploma (Sports Physiotherapy), La Trobe University, Australia. This thesis is submitted for the Doctor of Philosophy February, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Australia 1

2 Notice 1 Under the Copyright Act 1968, this thesis must be used only under the normal conditions of scholarly fair dealing. In particular no results or conclusions should be extracted from it, nor should it be copied or closely paraphrased in whole or in part without the written consent of the author. Proper written acknowledgement should be made for any assistance obtained from this thesis.

3 TABLE OF CONTENTS LIST OF TABLES... 6 LIST OF FIGURES... 8 LIST OF PUBLICATIONS ARISING FROM THIS THESIS LIST OF PRESENTATIONS ARISING FROM THIS THESIS OTHER PUBLICATIONS ABSTRACT STATEMENT OF ORIGINALITY ACKNOWLEDGEMENTS CHAPTER 1: INTRODUCTION Thesis Aims and Hypotheses Thesis Style Thesis Chapters CHAPTER 2: INJURY SURVEILLANCE IN ELITE SRI LANKAN CRICKET PLAYERS: FAST BOWLERS ARE MORE SUSCEPTIBLE TO INJURIES Methods Results Discussion Conclusion

4 CHAPTER 3: LITERATURE REVIEW OF LUMBAR BONE STRESS INJURIES IN CRICKET FAST BOWLERS Terminology Epidemiology of spondylolysis in fast bowlers Anatomical characteristics of lumbar bone stress injuries Why is the L5 vertebra most vulnerable to bone stress injury? Pathogenesis of lumbar bone stress injuries Mechanism for bone stress at the lumbar pars interarticularis in fast bowlers Pars defects and pain Sclerosis Disc degeneration, fast bowling and pars defects Risk factors in the development of lumbar bone stress injury in fast bowlers Investigations Management Conclusion CHAPTER 4: MEASURING QUADRATUS LUMBORUM CROSS SECTIONAL AREA USING MAGNETIC RESONANCE IMAGING: REVIEW AND JUSTIFICATION OF METHODS Methods Results

5 4.3 Conclusion CHAPTER 5: QUADRATUS LUMBORUM ASYMMETRY AND LUMBAR SPINE INJURY IN ELITE ADOLECENT CRICKET FAST BOWLERS Methods Results Discussion Conclusion CHAPTER 6: ADULT CRICKET FAST BOWLERS WITHOUT LOW BACK PAIN HAVE LARGER QUADRATUS LUMBORUM ASYMMETRY THAN INJURED BOWLERS Methods Results Discussion Conclusion CHAPTER 7: THESIS DISCUSSION Thesis Aims Other findings Thesis Limitations Conclusion REFERENCES

6 APPENDICES Appendix A International Cricket Council Member Countries and Membership Appendix B The Fundamentals of Cricket Appendix C Cricket Specifics Appendix D Fast Bowling Biomechanics and Techniques Appendix E List of Abbreviations Appendix F - Publications Arising From This Thesis

7 LIST OF TABLES Table 1.1 Average weather temperatures in key cricket playing cities.20 Table 2.1 Match Incidence per country (injuries per 10,000 player hours)...29 Table 2.2 Methods used to determine seasonal incidence.39 Table 2.3 Match incidence and exposures for player positions (Sri Lankan cricket team) Table 2.4 Match incidence by season (Sri Lankan cricket team)..44 Table 2.5 Number of cricket exposures and injury incidence for ODI cricket Table 2.6 Number of cricket exposures and injury incidence for Test cricket..46 Table 2.7 Seasonal incidence for the Sri Lankan cricket team..47 Table 2.8 Injury prevalence for both Test and OD matches for the Sri Lankan cricket team 48 Table 2.9 Injury prevalence (%) for injury types (Sri Lankan cricket team) Table 2.10 Prevalence for each player position (%) in the Sri Lankan cricket team.50 Table 2.11 Games missed per season (Sri Lankan cricket team)..51 Table 2.12 Matches missed per injury category (Sri Lankan cricket team)..52 Table 2.13 Number game-days missed per injury (Sri Lankan cricket team) Table 3.1 The role of imaging at different stages of the bone stress continuum. 102 Table 4.1 Key characteristics of studies involving QL CSA and asymmetry.129 Table 4.2 Methods used to measure QL CSA in previous studies Table 4.3 MRI image quality scale for measuring QL CSA

8 Table 5.1 Adolescent fast bowler characteristics and key findings using two measurement methods Table 5.2 Example of calculation method for QL asymmetry Table 5.3 Magnitude of QL asymmetry in adolescent fast bowlers 155 Table 5.4 Asymmetry categories and dominance for adolescent fast bowlers Table 5.5 Comparison between measurement Method 1 and Method 2 for determining QL CSA Table 5.6 General characteristics for adolescent fast bowlers Table 5.7 Radiological status of adolescent fast bowlers at baseline and during the season Table 5.8 Injury status and magnitude of QL asymmetry for adolescent fast bowlers Table 5.9 Bone stress injury status and QL asymmetry for adolescent fast bowlers Table 6.1 Distribution of QL asymmetry dominance in adult fast bowlers Table 6.2 Injury and anthropometry for adult fast bowlers Table 6.3 Distribution of injury (%) and magnitude of QL asymmetry for adult fast bowlers Table 6.4 Odds Ratio for QL asymmetry status and lumbar bone stress injury in adult fast bowlers Table A.1 List of ICC member countries Table A.2 List of full ICC member countries and year of inclusion

9 LIST OF FIGURES Figure 2.1. Calculation of player hours of exposure per team...37 Figure 2.2 Number days to return from injury (LL = lower limb) in the Sri Lankan cricket team (y axis = number days missed due to injury, x axis =injury) Figure 3.1 Sagittal CT scan of the pars interarticularis (circled area) Figure 3.2 X-ray (arrow) and Scotty Dog (circle) appearance of lumbar pars interarticularis stress fracture ( Figure 3.3 SPECT scan appearance of lumbar bone stress injury (arrows).105 Figure 3.4 Computed tomography scan of chronic non-united (thick circle) and acute (thin circle) pars defect 107 Figure 3.5 Axial T2 fat suppressed MR image of the L3 pars interarticularis bone oedema (circle) consistent with bone stress injury 110 Figure 3.6 MRI of stress fracture in the region of the pars interarticularis evidenced by bone oedema and a fracture line..110 Figure 4.1 Model of the fascicles of quadratus lumborum. The small black arrow depicts lumbocostal fascicles. The larger white arrow models the iliolumbar, iliocostal and iliothoracic fascicles. (Phillips, Mercer, & Bogduk, 2008) Figure 4.2 Models of the anterior, middle and posterior layers (from left to right) for quadratus lumborum (Phillips, et al., 2008).122 Figure 4.3 Defining vertebral segments on MRI between upper vertebral endplates of the vertebra above and below (red lines) Figure 4.4 Example of low quality image (0/3 points) for QL from the quality imaging scale in Table 4.3. Note the superimposing of QL borders with psoas and erector spinae (ES)

10 Figure 4.5 Example of low quality image (1/3 points) from the quality imaging scale in Table 4.3. Note that QL muscle borders are not clearly visible and there is superimposing of QL borders with surrounding muscles. There is also some movement artifact, particularly on the right side of the image (wave lines within blue circle)..143 Figure 4.6 Example of high quality image (2/3 points) for QL on the right (arrow) from the quality imaging scale in Table 4.3. Note the one blurred border between QL and erector spinae (ES) group.144 Figure 4.7 Example of the highest quality image (3/3 points) for QL from the quality imaging scale in Table 4.3. Note that all borders are clearly visible and easy to differentiate from other structures Figure B.1 Description of BFC (left) and FFC. Drawing adapted from Portus et al. (2004) Figure B.2 Description of front on bowling technique. Drawing adapted from Portus et al. (2004) Figure B.3 Description of side-on bowling technique. Drawing adapted from Portus et al. (2004)..233 Figure B.4 Description of semi-open bowling technique. Drawing adapted from Portus et al. (2004)..234 Figure B.5 Description of mixed bowling technique. Drawing adapted from Portus et al. (2004) Figure B.6 Description of SCR during delivery stride. Drawing adapted from Portus et al. (2004)

11 LIST OF PUBLICATIONS ARISING FROM THIS THESIS 1. Kountouris, A., Portus, M., & Cook, J. (2012). Quadratus lumborum asymmetry and lumbar spine injury in adolescent cricket fast bowlers. Journal of Science and Medicine in Sport, 15, Kountouris, A., Portus, M., & Cook, J. (2012). Quadratus lumborum asymmetry is not isolated to the dominant side in junior cricket fast bowlers. British Journal of Sports Medicine, 46, Kountouris, A., Portus, M., & Cook, J. (2013). Cricket fast bowlers without low back pain have larger quadratus lumborum asymmetry than injured bowlers. Clinical Journal of Sport Medicine, 23,

12 LIST OF PRESENTATIONS ARISING FROM THIS THESIS 1. Lumbar stress fractures in cricket fast bowlers. SPA / SMA Injury Prevention Conference, Melbourne, May, Quadratus lumborum asymmetry in cricket fast bowlers. Cricket Australia Sports Science and Sports Medicine Conference, Gold Coast, June, Lumbar stress fractures in cricket fast bowlers. Johannesburg, South Africa. April

13 OTHER PUBLICATIONS 1. Kountouris, A., & Cook, J. (2007). Rehabilitation of Achilles and patellar tendinopathies. Best Practice and Clinical Rheumatology, 21(2), Orchard, J., James, T., Portus, M., Kountouris, A., & Dennis, R. (2009). Fast bowlers in cricket demonstrate up to 3- to 4-week delay between high workloads and increased risk of injury. American Journal of Sports Medicine, 37(6), Orchard, J., & Kountouris, A. (2011). The management of tennis elbow. British Medical Journal, 342, Orchard, J., James, T., Kountouris, A., & Farhart, P. (2011). Cricket Injuries. In M. Hutson & C. Speed (Eds.), Sports Injuries (pp ). Oxford: Oxford University Press. 12

14 ABSTRACT The purpose of this thesis was to examine the nature and extent of cricket fast bowling injuries. In particular, the thesis investigated the risk factors for the lumbar bone stress injuries with particular emphasis on exploring whether paraspinal muscle asymmetry is a genuine risk factor and previously identified. A secondary aim was to determine if the previously published injury surveillance data that highlighted a high injury incidence, prevalence and severity of fast bowling injuries, such as lumbar bone stress injuries also existed in elite Sri Lankan fast bowlers. The results from this thesis confirm that elite level Sri Lankan fast bowlers have higher injury incidence and prevalence compared to other player positions. In particular, lumbar bone stress injuries were the most severe injury and resulted in the most gamedays missed. A review of published literature demonstrated that lumbar bone stress injuries occur near the biomechanically vulnerable region of the pars interarticularis, at the posterior element of the vertebra. There were numerous risk factors identified, including bowling technique, workload and more recently quadratus lumborum (QL) muscle asymmetries. The latter part of the thesis explored the methods used to measure the magnetic resonance imaging (MRI) derived QL cross-sectional areas that have been used to determine asymmetry. A method for measuring QL from MRI was proposed and tested in subsequent chapters, demonstrating reliable measurements. 13

15 Finally, MRI scans performed in asymptomatic adolescent and adult fast bowlers were reviewed and QL asymmetries reported. As expected large QL asymmetries were found in both groups but the pattern of asymmetry differed, with adolescents having an even distribution of larger sized QL muscles on both sides, whereas adult fast bowlers had larger muscle size (asymmetry) favouring the QL on bowling-arm side. The differences between the groups were explained by potential age related factors such as chronic bowling workloads and possibly bowling technique differences. In the participants studied, QL asymmetries were not associated with increased risk of lumbar spine injury in either adult or adolescent bowlers. These results question the previously published links between QL asymmetry and lumbar spine injury in fast bowlers. More research is required to determine the relationship between bowling technique, bowling workloads, muscle asymmetry and lumbar spine injury. This may determine if there is an algorithm of factors that are related to lumbar spine injury in cricket fast bowlers. 14

16 STATEMENT OF ORIGINALITY I declare that this thesis is my own original work and contains no material which has been accepted for the award of any other degree or diploma in any university or other institution. To my best knowledge the thesis contains no material previously published or written by another person, except where due reference is made in the text of the thesis and works that have been published during the completion of this thesis. Under the Copyright Act 1968, this thesis must be used only under the normal conditions of scholarly fair dealing. In particular no results or conclusions should be extracted from it, nor should it be copied or closely paraphrased in whole or in part without the written consent of the author. Proper written acknowledgement should be made for any assistance obtained from this thesis. I certify that I have made all reasonable efforts to secure copyright permissions for thirdparty content included in this thesis and have not knowingly added copyright content to my work without the owner's permission. Alex Kountouris 15

17 ACKNOWLEDGEMENTS The author of this thesis would like to acknowledge the support of Cricket Australia s Centre of Excellence for funding part of the project where some of the data for this study was collected, in particular, the support of Dr. Marc Portus who coordinated the larger project. The analysis of quadratus lumborum data was funded by Cricket Australia through its Sports Science and Medicine Research Program. Acknowledgement is also required for the numerous sports science and sports medicine people involved in the part of the project that included the participants scans, collection of anthropometry and injury data. Sri Lanka Cricket (previously Board of Control for Cricket in Sri Lanka) also provided support for the injury surveillance study and need acknowledgment, as do the players of the Sri Lankan Cricket national cricket team for participating in the study. Finally, this thesis would not be possible without the support of my supervisor, Professor Jill Cook, who provided the guidance required to produce this thesis, statistical support for the research studies and moral support since the start of the project. 16

18 CHAPTER 1: INTRODUCTION Lumbar spine stress fractures are common in cricket fast bowlers and result in long periods out of the game. Despite this, cricket is considered to be a sport with only a moderate injury risk, mainly because the risk to an individual player is linked to their playing role. Previous research has demonstrated variability in injury characteristics associated with playing position (Leary & White, 2000; Mansingh, Harper, Headley, King-Mowatt, & Mansingh, 2006; Newman, 2003; Orchard, James, & Portus, 2006; Stretch, 2003). The difference in injury type, prevalence and severity encountered by different player positions may be a reflection of the diversity in biomechanics and workloads associated with each position. In particular, fast bowling is thought to lead to injury because of its high vertical impact forces coupled with unnatural trunk positions placing considerable stress on spinal segments (Ferdinands, Kersting, & Marshall, 2009; Portus, 2001; Ranson, Burnett, King, Patel, & O'Sullivan, 2008) and because bowlers at the elite level are expected to bowl excess of 5000 deliveries per year. Injury surveillance studies provide evidence that fast bowlers are at higher risk of injury and suffer from more debilitating injuries than players in other positions (Newman, 2003; Orchard, et al., 2006; Stretch, 2003). In particular, lumbar spine stress reactions and fractures (lumbar bone stress injuries) are relatively common in fast bowlers and require long recovery periods (Orchard, et al., 2006). Even more concerning is that this injury is common in both adolescent and adult fast bowlers (Engstrom & Walker, 2007; Foster, John, Elliott, Ackland, & Fitch, 1989; Ranson et al., 2008). There no single factor that has been identified as the cause of lumbar bone stress injuries in fast bowlers, despite much research over the past 20 years. The main risk factors identified are related to 17

19 bowling technique and workload (Dennis, Farhart, Goumas, & Orchard, 2003; Elliott, Foster, & Gray, 1986; Elliott, Hardcastle, Burnett, & Foster, 1992; Elliott, John, & Foster, 1989; Foster, et al., 1989; Portus, 2001). As a result, much time and effort has been spent on correcting the technique and workload errors in an attempt to reduce injury rates. Despite this, lumbar bone stress injury rates have not improved over the past decade, which has led to the investigation of other potential risk factors (Engstrom, Walker, Kippers, & Mehnert, 2007; Hides et al., 2008; Orchard, et al., 2006; Ranson, Burnett, King, O'Sullivan, et al., 2008). One area that has been identified is the role of paraspinal muscle asymmetries in the development of this injury. In particular, quadratus lumborum (QL) asymmetry in adolescent and adult cricket fast bowlers (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008) has been shown to be associated with and a risk factor for, lumbar spine injury, which interests researchers, coaches and administrators who have an interest in injury prevention. This has resulted in debate about the role of QL and how it may relate to lumbar stress injury (de Visser, Adam, Crozier, & Pearcy, 2007). Although hypertrophic muscle development around the spine has been hypothesised as a mechanism of injury, others have reported no relationship between QL asymmetries and lumbar spine injury (Ranson, Burnett, King, O'Sullivan, et al., 2008), creating doubt about its role in lumbar spine fast bowling injury. The consensus from the available research is that lumbar bone stress injuries are caused by multiple factors. One factor that has not been investigated is whether the different conditions between cricket playing countries are related to injury. Injury rates reported in the South African national team differed on home and away cricket tournaments, suggesting that differences could be expected in injury profiles when teams 18

20 played in different locations in the world. It is therefore reasonable to expect that injury surveillance studies should be conducted in all major cricket playing nations. The majority of cricket related epidemiology research has come from Australia (Orchard, et al., 2006), England (Leary & White, 2000; Newman, 2003) and South Africa (Stretch, 1995, 2001b, 2003; Stretch & Raffan, 2011; Stretch, Raffan, & Allan, 2009). More recently, injury surveillance studies have also been reported from New Zealand (W. Frost & Chalmers, 2012) and West Indies (Mansingh, et al., 2006), but there is still no injury surveillance data published from the Indian subcontinent teams (India, Sri Lanka, Pakistan and Bangladesh). As great diversity is expected in playing conditions between cricket playing countries, it is possible that injury characteristics may be differ. For example, Australia and South Africa are considered to be conditions that are more favourable for faster bowlers compared to Indian subcontinent nations, where slow bowlers are considered to be more effective. It is possible that fast bowlers are favoured in some countries because pitches are harder and therefore bouncier or faster. The hardness of pitches may result in greater impact forces and possibly more bone stress injuries, alternatively more favourable fast bowling conditions may mean that fast bowlers have greater workloads and increased injury risk. Additionally, weather conditions vary between countries that may affect dehydration, fatigue and ultimately injury risk (Table 1.1). Bowling longer bowling spells has been shown to result in alterations in technique that may predispose bowlers to injury (A. Burnett, Elliott, & Marshall, 1995). These changes are thought to be fatigue related, so it is likely that hotter conditions could result in earlier fatigue and therefore increase injury risk. For these 19

21 reasons, injury surveillance studies from all cricket playing nations are required to determine all possible injury risk factors. Table 1.1 Average weather temperatures in key cricket playing cities ( Key cricket playing cities Temperature Auckland Colombo Johannesburg London Melbourne Mumbai Average high temperature (Degrees Celsius) Average low temperature (Degrees Celsius) The purpose of this thesis was to investigate if fast bowling injury characteristics differ in the teams from the Indian subcontinent with those previously reported in Australia, South Africa, England, New Zealand and West Indies. Additionally, the thesis will explore whether the paraspinal asymmetries that have been previously reported as 20

22 possible risk factors for lumbar bone stress injuries exist in adolescent and adult cricket fast bowlers and if they are related to injury. The game of cricket To understand the relationship between fast bowling injuries and the game of cricket, it is important to understand some of the basic principles of cricket. The list cricket playing nations are outlined in Appendix A. The rules of cricket are complex and beyond the scope of this thesis however Appendix B provides a description of the most basic rules and principles of cricket. As discussed above, player positions / roles vary considerably and related to injury rates. Additionally, cricket is unique as different formats of cricket have different physical demands that may also affect injury rates. Appendix C includes a detailed description of the player positions and the different level of cricket tournaments. 1.1 Thesis Aims and Hypotheses The aims of this thesis were to: 1. Examine the epidemiology of cricket injuries in Sri Lankan players 2. Assess whether Sri Lankan fast bowlers had similar injury characteristics as elite bowlers from other parts of the world. 3. Develop methods of measuring paraspinal muscle size 4. Describe the paraspinal muscle morphology of adolescent and adult cricket fast bowlers 5. Investigate the association between paraspinal muscle asymmetries and lumbar spine injuries in cricket fast bowlers. 21

23 The null hypothesis was taken when there was no previous research. The hypothesis for each of the aims is: 1. Sri Lankan cricket players will have similar injury epidemiology as players from other countries 2. Sri Lankan fast bowlers will have the same injury epidemiology as players from other countries 3. The methods of measuring paraspinal muscle size will be limited by methodological issues. 4. That cricket fast bowlers have large paraspinal asymmetries. 5. Large paraspinal asymmetries will be associated with lumbar spine injuries in cricket fast bowlers 1.2 Thesis Style This thesis will follow the American Psychological Association (APA) style of writing and will use Australian English spelling and grammar. 1.3 Thesis Chapters The order and rationale for the chapters in this thesis is outlined below: Chapter 1 was the introduction to the thesis and included identification of gaps in the current cricket injury literature. It included the thesis aims and justification that the research was important to the field of cricket injury. 22

24 Chapter 2 involved a prospective injury surveillance study of elite Sri Lankan cricket players over two cricket seasons. The data was used to determine the extent of the problem being investigated; fast bowling injuries, and identify specific injuries that need further investigation. Chapter 3 involved a literature review of the one specific injury (lumbar bone stress injury) that was identified in the epidemiological study in Chapter 2. It included a review of risk factors for lumbar bone stress injury and highlighted the emergence of a recent risk factor, QL asymmetry that required further investigation. Chapter 4 included a review of methods used to determine QL asymmetry through measurements of muscle cross-sectional area (CSA) using modern imaging techniques. Specific issues associated with measuring QL based on its specific anatomy were identified and a protocol was developed to measure QL from MR imaging. Chapter 5 was a prospective study investigating the link between QL asymmetry and lumbar spine injury in adolescent cricket fast bowlers, using the methods developed in the previous chapter. Chapter 6 also examined the links between QL asymmetry and fast bowling injuries in adult elite level fast bowlers. Comparison was made between the adult group in this chapter and the adolescents in Chapter 5. Chapter 7 was the thesis summary and addressed each of the thesis aims identified in Chapter 1, including recommendations for future research. 23

25 CHAPTER 2: INJURY SURVEILLANCE IN ELITE SRI LANKAN CRICKET PLAYERS: FAST BOWLERS ARE MORE SUSCEPTIBLE TO INJURIES In sport, injury surveillance forms the basis for injury prevention and intervention programs (van Mechelen, 1997, 1998). A key component of any injury surveillance program is consistent terminology and definitions, so comparisons can be made within the same sport between different countries or competitions, and between different sports (Orchard et al., 2005; van Mechelen, 1997). Cricket was the first major sport to reach a consensus on injury surveillance definitions and methods of data collection (Orchard, et al., 2005). In cricket, injury surveillance data has been published from some of the major cricket playing nations including Australia (Orchard & James, 2004; Orchard, James, Alcott, Carter, & Farhart, 2002; Orchard, et al., 2006), South Africa (Stretch, 2003; Stretch & Raffan, 2011; Stretch, et al., 2009), England (Leary & White, 2000; Newman, 2003), West Indies (Mansingh, et al., 2006) and most recently New Zealand (W. Frost & Chalmers, 2012). Despite having the most International Cricket Council countries, there are no published injury surveillance data from teams in the Indian subcontinent (India, Sri Lanka, Pakistan and Bangladesh). The earliest injury surveillance data to be published was a retrospective study involving English first class cricket players competing at domestic (national) level (Leary & White, 2000). This was followed by a prospective study of English domestic and international players over one competitive season (Newman, 2003). Stretch (2003) also 24

26 reported prospective injury data from international and domestic level South African cricket teams over three consecutive cricket seasons. The most comprehensive cricket injury reports to be published have been from Australia, where Orchard et al (2002) reported injury surveillance data for six consecutive cricket seasons. Since then, the consensus statement for injury surveillance methods in cricket was published and there have been five injury reports published on domestic and international cricket players from the West Indies (Mansingh, et al., 2006), Australia (Orchard, et al., 2006), South Africa (Stretch & Raffan, 2011; Stretch, et al., 2009) and New Zealand (W. Frost & Chalmers, 2012) that have largely conformed to the consensus statement. Mansingh et al (2006) reported a prospective injury surveillance program of domestic and international level West Indian cricket over one year. The South African group used the international definitions to report injury patterns of domestic and international cricket players over a two year period (Stretch & Raffan, 2011; Stretch, et al., 2009). Orchard et al. reported injuries in Australian domestic and international cricket over a 10 year period, which was, in essence, an extension of the 2002 report (Orchard, et al., 2002; Orchard, et al., 2006). The most recent injury report to be published, involved New Zealand players competing in domestic and international competitions over six consecutive years. Whilst this study began before the consensus of injury definitions was published, the data were adjusted to conform to the definition retrospectively. This was also the first study to report injury data from domestic and international T20 competitions. The simplest way to compare injury rates between different countries is to examine injury incidence, which is a measure of new injuries over a specified period 25

27 adjusted for exposure. The match incidence reported to date is outlined in Table 2.1. Whilst the Australian, West Indian, New Zealand and South African data conformed to the international definition of incidence, the definition used in the Newman (2003) study is unknown. Consistently, different formats of the game resulted in different injury incidence. The match and seasonal injury incidence for the two traditional game formats demonstrated differences between the limited overs and longer versions (Mansingh, et al., 2006; Newman, 2003; Orchard, et al., 2006). Orchard et al. (2006) reported that over a 10 year period, One-Day International (ODI) games had higher match injury incidence compared to Test matches, domestic first-class matches and domestic One-Day (OD) games. Similarly, Frost and Chalmers (2012) reported that the match incidence in ODI (73.1 injuries per 10,000 player hours) was twice that of Test matches (30.1 injuries per 10,000 player hours) however, the difference was not as large between domestic OD games (36.2 injuries per 10,000 player hours) and first class (24.1 injuries per 10,000 player hours) matches. This difference between international and domestic game formats was in the opposite direction in the West Indian (Mansingh, et al., 2006) and most recent South African (Stretch & Raffan, 2011; Stretch, et al., 2009) studies, with higher match incidence in Test matches than ODI. Whilst the data reported by Australian and New Zealand studies suggests that the longer versions of the game are safer than limited overs matches, it is somewhat misleading, as one study demonstrated a 3-4 week lag between high match bowling workloads and injury (Orchard, James, Portus, Kountouris, & Dennis, 2009). It is common place that ODI games are typically scheduled after the conclusion of Test series so it is likely that some injuries sustained in ODI matches may be as a result of the pre- 26

28 existing high workloads from the preceding longer match versions. It is therefore possible that scheduling differences may explain the disparity in results between these studies and the West Indian and South African data. The seasonal incidence, which includes both training and match injuries over a specified period (season), was also was reported (using the internationally accepted definition) by Orchard et al. (2006) as a 10-year mean of 16.3 injuries per squad per season. Frost and Chalmers (2012) reported seasonal incidence separately for international ( injuries per squad per season) and domestic ( injuries per squad per season) competitions. Newman (2003) reported the seasonal incidence for English cricket as 8.6 injuries per squad per season (range ) but the definition of seasonal injury in this study was not stated so comparisons are not possible. The seasonal incidence was not reported in any other cricket injury surveillance studies published. Injury prevalence, which is the percentage number of players missing due to injury at any given time (see formal definition in Section 2.1, Chapter 2) and representative of injury severity, steadily increased, with a mean of 9.1% over the 10 years in the Australian study (Orchard, et al., 2006), whilst fluctuating in the six years of the New Zealand study with a mean of 10.2% (W. Frost & Chalmers, 2012). In one season of elite English cricket the injury prevalence was slightly higher (12.3%), although in this study the methods of calculating prevalence were not reported (Leary & White, 2000). The mean yearly injury prevalence was also reported for different game formats with 7.5% (3.3 to 11.5%) for Test and 9.4% (3.8 to 14.4%) ODI matches respectively in the Australian study compared to 11.3% for Test matches and 8.1% for ODI matches in the West Indies study, (Mansingh, et al., 2006). The ODI and Test match 27

29 prevalence was not reported in the English and New Zealand studies, but Frost and Chalmers (2012) did report significantly higher prevalence rates between international (12.3%) and domestic (9.7%) competitions although Orchard et al. (2006) reported no difference between international (8.5%) and domestic (9.3%) competitions. A consistent finding from published cricket injury surveillance studies was that injury characteristics were related to playing position, with fast bowlers at greater injury risk compared to other players. Fast bowling accounted for a higher proportion (45%) of injuries in elite Australian cricket players, compared to other playing positions (batting 21% and fielding 23%) (Orchard, et al., 2006). Similarly, fast bowling was the most common injury activity (48.7%) in the New Zealand study (W. Frost & Chalmers, 2012). Fast bowlers also miss more games due to injury than other players with injury severity consistently higher than other playing positions in the Australian and New Zealand studies. Newman (2003) and Leary and White (2000) also respectively reported higher injury rates in elite English fast bowlers, as they accounted for 48% of games missed and higher injury incidence than other players. Stretch (2003) reported a similar trend in elite South African cricket players, with fast bowling accounting for the 41% of all injuries and the bowling delivery stride the most common mechanism of injury associated with 26% of all injuries. More recent South African studies have also confirmed that bowling was the most common injury mechanism in both domestic and international cricket players (Stretch & Raffan, 2011; Stretch, et al., 2009). 28

30 Table 2.1 Match incidence per country (injuries per 10,000 player hours) Type / level of cricket matches Country of study All cricket matches Test ODI Domestic 1 st class Domestic OD Australia 10 years (Orchard et al., 2006) West Indies 1 year (Mansingh et al., 2003) N/A England 1 year (Newman, 2003) N/A New Zealand 6 years (Frost & Chalmers 2012) N/A South Africa 2 years (Stretch & Raffan, 2011; N/A Stretch, et al., 2009) Note. N/A = not available 29

31 Injury can also be reported for each playing position and body region using injury prevalence. Orchard et al. (2006) reported that fast bowlers had the highest prevalence over a 10 year period (14.4%; range 9.3 to 19.5%) compared to batsman (4.3%; range 0.8 to 9.5%), spin bowlers (3.7%; 0.6% to 10.0%) and wicket-keepers (2.0%, range 0.4 to 3.7%). They also reported that the low back region had the highest prevalence (1.7%; 0.8% to 3.1%), followed by the combined shin/foot/ankle region (1.4%, range %) and groin/buttock/thigh region (1.3%; 0.7% to 2.0%). Frost and Chalmers (2012) also reported that fast bowlers (18.7%; 18% to 19.3%) had the highest prevalence compared to batsmen (5.4%; 5.1% to 5.8%), spin bowlers (5.5%; 4.8% to 6.3%) and wicket-keepers (3.8%; 3.1% to 4.5%) with the lower limb (46.3%) region being most frequently injured followed by trunk / back region (25.1%) The lumbar spine was also the most common region injured in the English study accounting for 14% of all injuries (Newman, 2003) but the definition for prevalence used (the percentage of players missing per match) was different to international consensus definition making comparisons difficult. The recent South African studies reported the proportion of injuries in each major body region instead of prevalence (Stretch & Raffan, 2011; Stretch, et al., 2009). The lower limb was the most commonly injured region in both domestic and international players, followed by the upper limb and the lower back / trunk regions. A weakness of injury prevalence as a measure of injury severity is that it is dependent on the amount of games scheduled over a given period and therefore influenced by how congested the playing schedule was from year to year, with more games missed per injury (higher prevalence) during busier periods. For example, a major injury that results in a player being unavailable from competitive games for three months 30

32 may result in relatively low injury prevalence if it occurs at the end of a cricket season and includes a large part of the off-season. In comparison, a less serious injury that could result in a three week absence from playing would have in higher injury prevalence if more matches were scheduled during that period. For this reason the cost of an injury in terms of time or game-days missed, is arguably a better indication of injury severity than prevalence although game-day missed is similarly influenced by scheduling. Gamedays missed were not recorded in the most comprehensive of injury surveillance program, the 10-year Australian study (Orchard, et al., 2006) and not part of the international definition (Orchard, et al., 2005). It was, however, reported in the abbreviated (six-year) injury surveillance paper in Australian cricket by the same authors (Orchard, et al., 2002). In this report they demonstrated that lumbar bone stress injuries resulted in the most game-days missed and had the highest injury prevalence compared to all other injury categories (Orchard, et al., 2002). Similarly, lumbar bone stress injuries resulted in the most game days missed due to injury in both the England (11% of gamedays missed) and New Zealand (22% 11% of game-days missed) (W. Frost & Chalmers, 2012; Newman, 2003). Game-days missed were not reported in the West Indies injury study (Mansingh, et al., 2006) but they did report on how many players missed more or less than 21 game days due to injury (44% of players missed more than 21 game-days) with fast bowlers (41%) making up the majority of players that missed more than 21 days (batsmen 36%). Stretch (2003) reported that 26% of the elite South African players were unable to play or train for longer than 21 days but did not report for specific player roles. Besides the high injury prevalence and severity, lumbar bone stress injury is also concerning because it is an injury that is common amongst younger athletes (Campbell, 31

33 Grainger, Hide, Papastefanou, & Greenough, 2005; Congeni, McCulloch, & Swanson, 1997; Dubousset, 1997). In cricket, it also commonly reported in younger players (Engstrom & Walker, 2007; Foster, et al., 1989; Hardcastle et al., 1992; Stretch, 1995, 2003). Stretch (2003) reported that the majority of injuries during their surveillance period involved players aged between years of age and that all fast bowlers (n=14) who developed symptomatic lumbar bone stress injuries were under the age of 24 years. Engstrom et al. (2007) reported that 20% of adolescent (13-17 year old) fast bowlers developed symptomatic lumbar stress fractures over four cricket seasons. Stretch and Trella (2012) reported that 10% of all injuries were stress fractures of the spine and trunk, in cricket players competing in national age group tournaments (under years of age). The major injury surveillance studies of adult elite level cricket players, however have not reported age as a factor for specific injuries. Future cricket related injury surveillance studies should examine the impact of age on injury, because age has been previously associated with increased injury risk for certain injuries in other sports (Bennell et al., 1998; Orchard, 2001). Finally, the cost of specific injuries may also be determined by the recurrence rate of injuries. Injury recurrence rates as high as 30% have been reported in Australian Football (Orchard & Seward, 2002). A common finding amongst the published cricket injury surveillance studies was that the majority of injuries (80-92%) were categorised as new injuries, although the recurrence rates for specific injuries were not reported (Mansingh, et al., 2006; Orchard, et al., 2006; Stretch, 2003; Stretch & Raffan, 2011; Stretch, et al., 2009). This is an important measure that needs to be reported in future injury surveillance studies. 32

34 A considerable gap in previously published cricket injury surveillance research was that there are no studies including teams from the Indian subcontinent, where unique playing conditions and possibly injury characteristics are expected (see Chapter 1). As such, the current study reported injury characteristics of elite cricket players based out of Sri Lanka and can be considered a sub-group of the Indian subcontinent, with particular emphasis on fast bowling injuries and whether lumbar bone stress injuries had the same impact as in injury surveillance studies in other countries. The aims of this study were to (a) compare elite Sri Lankan cricket players injury characteristics with players from other cricket playing nations (b) determine if Sri Lankan fast bowlers have similar injury rates as other international level fast bowlers (c) examine the impact of bone stress injuries in fast bowlers competing at international level and (d) compare the injury surveillance methods with those of the international consensus for cricket injury surveillance. 2.1 Methods Injury data was collected prospectively from the Sri Lankan national mens cricket team by the team physiotherapist (thesis author) over a 24 month period. The data was collected from April 2001 and concluded in April Ethics approval for the project was obtained through the Deakin University Human Ethics Committee. Injury Definition At the time when the data were collected for this study, there was no universally accepted definition of a cricket injury. The definition used in this study is similar to those 33

35 used in other cricket injury surveillance programs (Orchard, et al., 2002; Stretch, 2001a, 2001b) and to the internationally recognised definition of a cricket injury developed subsequently by Orchard et al (2005). In the current study, both injury or illness were referred to as injury and were included if they; 1. Resulted in a player missing part or all of a competitive international Test or ODI match. 2. Resulted in a player being unable to perform his normal positional duties during a competitive international match 3. Required surgery. Included because some surgery could be performed during periods when no matches were scheduled and missed as an injury statistic. This study only included injuries that occurred during preparation periods for international tournaments and during ODI and Test tournaments that involved the Sri Lankan national mens team during the two year surveillance period ( ). Injuries occurring during domestic competitions were excluded from injury surveillance. All injury surveillance was performed by the author of this thesis who was attached to the Sri Lankan national team as team physiotherapist. All injuries were defined as new or recurrent. Any injury that was reported for the first time by a player was defined as a new. A recurrent injury was defined as an injury of similar nature to an area previously reported by the player or was documented on previous medical records. 34

36 Participants The cohort consisted of 49 players with a mean age of 25.2 years (range years). Season 1 included 39 players and Season 2 had 34 players; of these 21 players were included in both seasons. There were 15 (31%) batsmen with mean age of 26.5 years (range 20-36), 22 (45%) fast bowlers with mean age of 23.8 years (range 19-33), eight (16%) spin bowlers with mean age of 25.4 years (range 19-30) and four (8%) wicket-keepers with mean age of 26.0 years (range 22-32). The age of the fast bowlers was significantly younger than the rest of the cohort (t-test p =.04). All players selected in the Sri Lanka national mens cricket team for official tournaments were included in the study from the time the national selection committee named a tournament squad, which included the preparation period preceding each tournament. Typically, large squads were selected initially and trimmed down closer the start of a tournament. Players omitted from the squads (not due to injury) prior to the commencement of the tournament were excluded from injury surveillance at the point of their omission. All injuries sustained during the surveillance period were included in the study until the player was deemed fit enough to be available for selection and remained in the surveillance squad until the next tournament squad was selected. This cohort design included only players involved in the national squad and competing at international level. This definition was also used as it allowed one person to collect the injury data. Typically, squads of players were selected for pretournament training periods and then this was be reduced to players for international level tournaments. 35

37 Player Positions The participants were designated as fast bowler, spin bowler, batsman or wicketkeeper. Whilst there is considerable overlap between positions with some participants being involved in more than one role, the primary role was chosen to categorise participants. Fast bowlers were players who regularly batted lower than number seven in the batting order and when bowling the wicket-keeper needed to stand away from the wickets for the majority of the time. This definition basically differentiates bowlers from batsmen, as most specialist batsman would be expected to bat in the top seven batting positions. It also differentiates faster bowlers from spin bowlers who would exclusively have the wicket-keeper positioned immediately behind the wickets. It does not differentiate the truly faster bowlers from medium pace bowlers. Spin bowlers were defined as any player batting lower than number seven in the batting position and regularly have the wicket-keeper positioned immediately behind the wickets. Batsmen were players who bat in the top seven batting positions and are not regular wicket keepers. Wicket-keepers were defined as players whose have been selected in a team as the dedicated wicket-keeper. Whilst this definition does not account for players who are all-rounders and are reasonably well proficient in more than one skills, it allows for clear categories to be created. The injury characteristics of specific skills will be included in the mechanism of injury, and include batting, bowling, fielding and wicket-keeping. 36

38 Match Injury Incidence Match injury incidence was defined as the number of injuries in competitive matches divided by the player exposure. Player exposure was calculated with both timebased and delivery based methods, similar to the internationally recognised definition (Orchard, et al., 2005). Match records were used to calculate the actual number of exposure overs bowled / fielded or batted in each days play, thus accurately calculating player exposure per team (Figure 2.1). Match injury incidence was calculated using both balls bowled and hours of exposure as the denominators for incidence calculation, to provide the utility so the results can be compared with other injury surveillance reports and is consistent with the international definition (Orchard, et al., 2005). Number of batting overs X 2 (No. of batsmen exposed at any given time) + Number of fielding overs X 11 (No. players on the field at any given time) = Total number of team player overs (per team) / 15 (standard no. of overs per hour of play) = Total player hours of exposure per team Figure 2.1. Calculation of player hours of exposure per team Calculating exposure was based on the match records and is more accurate than the consensus definition as there is no assumption of player exposure in terms of balls batted, fielded and bowled. The only assumption made in this study was that 15 overs 37

39 were bowled per hour during each days play, when calculating the time-based equation, but as this is a minimum requirement in the rules of the game it is anticipated that it is a true reflection of hours played. Seasonal Incidence Unlike domestic competitions, international cricket does not have easily defined cricket seasons. As such, this study was divided into two 12 months cricket seasons because the data were prospectively collected over a 24 month period. Matches during the surveillance period were sub-categorized as either Test or OD tournaments. Test tournaments consisted of matches played in a first-class format, OD tournaments consisted of ODI and any list-a matches. No T20 matches were played during this period. The formula used to calculate seasonal incidence was the same as the international definition (Orchard, et al., 2005). The number of days used in the equation was the sum of all match days (Test and OD) completed during the surveillance period. Season 1 consisted of 84.5 completed match days and Season 2 consisted of completed match days with the entire 24 month period consisting of 192 completed match days (Table 2.2). During the two year surveillance period there were a total of 22 tournaments (10 in Season 1 and 12 in Season 2), which included 21 Test matches and 77 ODI s. The remainder of the match days included in the surveillance data were from firstclass practice matches during Test tours and non-international OD games during ODI in the preparation phase of some ODI tours. 38

40 In this study, the cricket season was considered to be a non-regular format and each tournament was considered a mini-season as changes to the playing squad (cohort) for each tournament were possible. The sum of the tournaments ( mini-seasons ) was used as the seasonal incidence denominator. To allow for comparison with other injury surveillance studies, the formula used included the average squad season of 1500 (25 players x 60 season-days), which was considered to be a rough estimate of squad-season in elite level cricket by Orchard et al. (2005) (Table 2.2). Table 2.2 Methods used to determine seasonal incidence A: Actual B: Squad Squad Orchard Proportional season incidence season numbers season squad- formula recommended by days (A x B) season Orchard et al. (2005) Season No injuries (Season 1) x 1500 / Season No injuries (Season 2) x 1500 / 3655 Seasons 1 & No injuries (Seasons 1 & 2) x 1500 /

41 Injury Prevalence Injury prevalence was defined as the percentage of squad members not available for selection for each match. For this study, prevalence was calculated using game-days missed and matches missed in order to compare Test matches with OD matches. The definition used was the same as Orchard et al. (2005), with the numerator being the games days missed and the denominator the number of completed games days multiplied by the number of squad members exposed in every game. Injury Severity Injury severity was not included in the international definitions paper but was reported in the current study as the number of games and days missed. An injury that led to a player missing one Test match (5 days) was recorded as a more severe injury when compared to a similar injury that led to a player missing a single one-day game. The mean number of game-days missed per injury was also reported. The number of days from injury to return to play is a reflection of the recovery period for each injury and was also recorded. To distinguish between injuries that resulted in longer recovery periods and to allow comparison with previous studies; the injuries were dichotomised into injuries requiring less than 21 days to return to playing and those greater than 21 days to return to play after injury. Workload analysis Test match bowling workloads were dichotomised for fast and spin (slow) bowlers. Additionally, the bowling for these two groups was also subcategorised to 40

42 reflect workloads in the Indian subcontinent region and the rest of the cricket playing nations. During the surveillance period, fast bowlers accounted for 46% of all Test matches overs bowled (spin bowlers = 54%). For Test matches played in the Indian subcontinent (16 of 21 Test matches); fast bowlers bowled 40% of overs and for games played outside that region, they bowled 64% of all Test match overs. Only Test match overs were considered in this section because it is in this format that disparity in workloads is likely to exist as no bowling restrictions apply as in ODI matches. Data analysis Injury data were recorded on a spreadsheet (Excel Microsoft Corporation, 2003). The odds ratio (OR) and the confidence intervals were calculated using the spreadsheet from the Pedro website ( Independent T-tests and Confidence Intervals of 95% were used to determine age differences between player position and the relationship of age between injured and uninjured players during the surveillance period. Significance level was set at p < Results Injury Characteristics Nineteen different players sustained a total of 47 injuries during the surveillance period, with eight players having multiple injuries. The mean age at the start of the surveillance period for injured players (25.4 years) was similar to those not injured (25.1 years) during the two cricket seasons (p =.86). 41

43 Seventeen (36%) of injuries resulted in missed matches and 3 (6%) injuries required surgery. Sixty-two percent of injuries were acute injuries, whilst 36 % of injuries were gradual onset (overuse) injuries. New injuries comprised 79% of all injuries and 21% were a recurrence of a previous injury. Injury and Player Position Fast bowlers accounted for 20 (43%) injuries, batsmen 17 (40%) injuries, spin bowlers 7 (15%) injuries and one (2%) wicket-keeper was injured. Of the 19 players to sustain at least one injury, the majority of injured players were fast bowlers (58%) followed by batsmen (26%), spin bowlers (11%) and wicket-keepers (5%). The odds ratio (OR) of a fast bowler sustaining an injury compared to the rest of group was 2.90 (95%CI = , p=0.08). When injuries were evaluated based on the mechanism of injury, the majority of injuries occurred whilst fielding (38%), followed by bowling (30%) and batting (17%). Pre-match warm-up activities resulted in 9% of injuries. Match Incidence There were a total of 39 injuries that occurred during matches and a match incidence for the surveillance period of 54.9 injuries per 10,000 player hours (Tables 2.3 and 2.4). The match incidence was also calculated for the different playing position (Table 2.3) and fast bowling had a match incidence more than three times higher than batting and seven times greater than fielding. 42

44 Table 2.3 Match incidence and exposures for player positions (Sri Lankan cricket team) Player position Exposure and injury Bat Bowling Fielding Total Number of cricket exposures (hours) Number of cricket exposures (overs) Number match injuries ª % Injuries Injury rate per; 10,000 playing hours ,000 balls bowled Note. ª that there was a difference between the sum of bat, fielding & bowling and total, because some injuries occurred during matches but not during batting, bowling or fielding 43

45 Season 1 versus Season 2 There were more match days played in Season 2 and the match incidence in Season 2 was also higher when compared to Season 1 (Table 2.4). Table 2.4 Match incidence by season (Sri Lankan cricket team) Cricket season Exposure Season 1 Season 2 All seasons Number of match days Player hours per team per day Match incidence per 10,000 player hours One-day versus Test Match Incidence There was a match incidence of injuries per 10,000 player hours in ODI matches and injuries per 10,000 player hours in Test matches (Tables 2.5 and 2.6). A comparison of match incidence between player positions in ODI and Test matches demonstrated that ODI match bowling injuries had a much higher match incidence 44

46 compared to all other player positions in both formats. The next highest match incidence was for Test match bowling and was still almost double the match incidence of any other position in either format of the game. Table 2.5 Number of cricket exposures and injury incidence for OD cricket Player position Exposure and injury Bat Bowling Fielding Total Number of cricket exposures (hours) Number of cricket exposures (overs) Number injuries ª % Injuries Injury rate per; 10,000 playing hours ,000 balls bowled

47 Table 2.6 Number of cricket exposures and injury incidence for Test cricket Player position Player position Bat Bowling Fielding Total Number of cricket exposures (hours) Number of cricket exposures (overs) Number injuries ª % Injuries Injury rate per; 10,000 playing hours ,000 balls bowled Note. ª that there is a difference between the total bat, fielding & bowling with total, because two injuries occurred during pre-match warm-up sessions and did not fit into batting, bowling or fielding categories. Seasonal Incidence The seasonal incidence, converted to a rate recommended by Orchard et al. (2005), for both seasons individually and for the entire surveillance period is outlined in 46

48 Table 2.7. The second season had almost double the seasonal incidence compared to the first season. Table 2.7 Seasonal incidence for the Sri Lankan cricket team Number of Squad Season match Season Season injuries numbers days Squad-season incidence Season Season Season 1& Prevalence The injury prevalence was calculated using both matches and match days to allow for better comparison between the two formats (Table 2.8). There was a higher total (Test and OD) prevalence in Season 1 (6.6%) compared to Season 2 (3.8%) and an overall prevalence of 5.4% (Table 8). There was higher injury prevalence for Test matches compared to OD matches in both seasons. The prevalence in Season 1 for Test matches more than three times higher than for OD games in the same period. In Season 2, Test match prevalence was twice as high as in OD matches. 47

49 Table 2.8. Injury prevalence for both Test and OD matches for the Sri Lankan cricket team Cricket season Type of match Season 1 Season 2 All Seasons OD match Test match Test days Total (Match days) Hand fractures, lower limb bone stress injuries, lumbar bone stress injuries and ankle injuries had the highest injury prevalence for specific injury types (Table 2.9). Fast bowlers had the highest injury prevalence followed by spin bowler and wicket-keepers. Interestingly batsmen had much lower injury prevalence than any other player position (Table 2.10). The OR of sustaining an injury that resulted in a game being missed based on playing position for a fast bowler compared to the rest of group was 4.28 (95%CI = , p=0.02). 48

50 Table 2.9 Injury prevalence (%) for injury types (Sri Lankan cricket team) Cricket season Injury type Season 1 Season 2 All seasons Hand fractures Lower limb bone stress injuries Lumbar bone stress injuries Ankle injuries Groin injuries Shoulder injuries Hamstring strains Knee injuries Quadriceps strains Illness

51 Table 2.10 Prevalence for each player position (%) in the Sri Lankan cricket team Cricket season Player position Season 1 Season 2 All seasons Fast Bowlers Spin Bowlers Batsmen Wicket-Keepers Injury Severity There were 105 games missed during the surveillance period (Table 2.11), which amounted to 216 game-days missed due to injury. Of the game-days missed due to injury over the entire surveillance period, fast bowlers accounted for the majority (67% of game-days missed), followed by spin bowlers (19%), wicket-keepers (11%) and batsmen (3%). When examining the data of games missed per injury; hand fractures, lumbar bone stress injuries and lower limb stress fractures resulted in the most games missed and the highest mean of games missed per injury (Table 2.12). 50

52 Table 2.11 Games missed per season (Sri Lankan cricket team) Games missed Cricket season ODI Test Total Season Season Total There were a total of 216 game-days missed due to injury, lumbar bone stress injuries (58 game-days missed and 27% of all days missed) and hand injuries (54 gamedays missed and 25% of all days missed) were the most severe injury during the surveillance period (Table 2.13). The mean number of game-days missed per injury showed bone stress injuries at the lumbar spine (29 games-days) and lower limb (32 game-days) were the most severe injuries (Table 2.13) and higher than the group mean of 12.7 days missed per injury. 51

53 Table 2.12 Matches missed per injury category (Sri Lankan cricket team) Injury type Test matches Games missed One-day games All games Number of injuries Average games missed per season Hand fractures Lumbar bone stress injuries Lower limb bone stress injuries Groin injuries Ankle injuries Shoulder injuries Hamstring strains Knee injuries Quadriceps strains Illness

54 Table 2.13 Number game-days missed per injury (Sri Lankan cricket team) Injury region Number gamedays missed Percentage of game-days missed Average game-days missed per injury Lower limb bone stress injuries Lumbar bone stress injuries Hand injuries Ankle injuries Shoulder injuries Groin injuries Knee injuries Hamstring strains Illness Quadriceps strains

55 The number of days taken to return from injury was also calculated for injuries that resulted in games missed. For this group of injuries the mean time missed due to injury was 51 days per injury (range days). The impact of the injury was more evident when injuries were subcategorised (Figure 2. 2). Lumbar bone stress injuries resulted in the most time recovering (201 days, 23% of all recovery days), followed by hand fractures (183 days, 21% of recovery days) and lower limb bone stress injuries (181 days, 21% of recovery days). When recovery days were compared to playing position, fast bowlers took the longest time to return from injury (mean of 54 days, range days) compared to the rest of the other playing positions (mean of 46 days, range 8-97 days). From the injuries that resulted in players missing more than 21 days of playing time, there were five fast bowlers, three spin bowlers and one wicket-keeper. [Type 250 a Number days missed 50 0 Hand Fracture LL Soft Tissue LL Bone Stress Lumbar Bone Joint Surgery Abdominal Stress Surgery Figure 2.2 Number days to return from injury (LL = lower limb) in the Sri Lankan cricket team (y axis = number days missed due to injury, x axis =injury) 54

56 2.3 Discussion This was the first study to evaluate injury surveillance data of an international level cricket team based in the India subcontinent and determine whether fast bowlers have the similar rates of injury as reported in other cricket playing nations (Mansingh, et al., 2006; Newman, 2003; Orchard, et al., 2006; Stretch, 2003). This study demonstrated that Sri Lankan fast bowlers were more susceptible to injury compared to other playing positions and that fast bowling was more likely to result in severe injuries, compared to other cricket activities. In particular, fast bowlers sustained more injuries than any other playing position, and had almost three times the odds of being injured than any other player role. Whilst this OR was not significant, this trend was likely a reflection of the small sample size. The trend for higher injury rates with fast bowling was more evident when match incidence was examined, which was more than three times greater for bowling, than batting and fielding, and peaked at a high of 304 injuries per 10,000 player hours for ODI cricket. Despite this high figure, fast bowling can still be considered a relatively low injury risk activity compared to elite rugby (839 injuries per 10,000 player hours), which is considered to be a high injury risk sport (Fuller, Laborde, Leather, & Molloy, 2008). Added to this, fast bowlers were most affected by markers of injury severity including higher injury prevalence, higher odds of sustaining an injury leading to missed games, most game-days missed due to injury and the longest time out of the game in the recovery post injury, when compared to other playing positions. The high injury prevalence for fast bowling rates in this study were consistent with previous cricket surveillance studies, and are an indication that fast bowlers sustain injuries that keep them out of the game for long periods. In particular, lumbar bone stress 55

57 injuries (stress reactions or stress fractures), are relatively common in cricket fast bowlers and result in long recovery times (Newman, 2003). In current study, despite only two injuries in this category during the two year surveillance period, it still resulted in the most game-days missed for any injury type, the most games missed per injury and was the injury with the longest recovery period (days to return to play). Added to this, lumbar bone stress injuries resulted in high injury prevalence with only hand fractures and lower limb bone stress injuries having higher prevalence rates. The low number of lumbar bone stress injuries in this study (9% of bowlers) is lower than the 43% (n=28) of English elite level bowlers who sustained lumbar bone stress injuries over a two year period (Ranson, Burnett, & Kerslake, 2010). The English bowlers were however not exclusively playing at international level, with most in development squads who were younger (mean age of 19.0 years) than the Sri Lankan cohort (mean age of 23.8 years). With age being possible risk factor for this type of injury, this could explain the difference in rates between the two groups. However, the Sri Lankan bowlers are still in the age range that is considered to be susceptible to bone stress injuries before physical (bone) maturity is reached (Been, Ling, Hunter, & Kalichman, 2011; Kroger, Kotaniemi, Kroger, & Alhava, 1993; Kroger, Kotaniemi, Vainio, & Alhave, 1992). The relative low number of lumbar bone stress injuries may also be related to the playing conditions and playing styles that differentiate the subcontinent teams from other cricket playing nations such England, New Zealand, South Africa and Australia. As discussed in Chapter 1, the playing conditions in the subcontinent are thought to be more conducive to slower bowlers, which may have resulted in lower fast bowling workloads 56

58 at times when the team was playing in Sri Lanka or other subcontinent destinations. This was confirmed in this study, as fast bowlers bowled 40% of all Test match overs in games played within the Indian subcontinent region and 64% of overs for matches outside this region. In the current study, 16 of the 21 Test matches were played in the Indian subcontinent (15 in Sri Lanka and one in Pakistan) and the other five Test matches were played in England and South Africa. During the same two year period ( ), Australian Test match bowlers accounted for 65% of all over bowled (35% for spin or slow bowlers) but this proportion did not change whether they were played matches on the Indian subcontinent or other parts other parts of the world ( This demonstrates that regional biases may account for differences in bowling workloads and may explain some variances in injury rates between different countries. Interestingly, one of the lumbar bone stress injuries occurred during the Test series in England, where fast bowlers were likely to bowl more, and the other just after the bowler had completed four consecutive Test matches where high workloads are likely. High bowling workloads (Dennis, et al., 2003) that are associated with Test match or first-class cricket have been previously linked to the development of injury in elite level fast bowlers (Orchard, James, Portus, et al., 2009). Both Mansingh et al. (2006) and Orchard et al. (2008) demonstrated differences in match injury incidence for tournaments played at home or away highlighting the change in player demands in different conditions (Mansingh, et al., 2006; Orchard, 2008). Finally, the injury rates for spin bowlers may demonstrate the difference in bowling workloads for players from different countries. Over a 10 year period of Australian cricket (Orchard, et al., 2006), the injury prevalence for spin bowlers was never higher than 10% (10 year mean of 3.7%) 57

59 but in the two years of the Sri Lankan data, spin bowlers had an injury prevalence of 12% and 14% for each of the respective years. These higher prevalence rates for spin bowlers may be indicative of the relative workloads and dependency that the Sri Lankan team had on slower bowlers. More research is required to determine if the bowling workloads differ between countries by taking training loads into consideration, and whether any workload differences between countries results in differences in injury characteristics. A common feature from all the injury surveillance programs published to date and consistent in the current study, was that fast bowlers were more adversely affected by injury than other players in the team (Leary & White, 2000; Mansingh, et al., 2006; Newman, 2003; Orchard, et al., 2006; Stretch, 2003). In particular, fast bowlers accounted for the most number of injuries and the highest injury prevalence (Mansingh, et al., 2006; Orchard, et al., 2006; Stretch, 2003). Another consistent finding was that fast bowlers were most affected when the measures for injury severity markers, such as most games missed, most game-days missed, injury prevalence and injuries with the longest recovery times were taken into consideration (Leary & White, 2000; Mansingh, et al., 2006; Orchard, et al., 2006; Stretch, 2003). This highlights the high physical demands that fast bowlers are exposed to and the long term injuries that result from repetitive high impact loading, which were evident in the current study with three bone stress injuries (two lumbar and one lower limb) that were all sustained by fast bowlers resulting in 42% of all games missed due to injury. One of the aims of this study was to compare injury characteristics of an Indian subcontinent team (Sri Lanka), with teams based in other parts of the world. As discussed, only 9% of bowlers in the Sri Lankan fast bowlers sustained lumbar bone 58

60 stress injuries, which much lower than the previously reported in Australian (Elliott, et al., 1992) and English (Ranson, et al., 2010) in elite fast bowlers. Another difference with in injury characteristics from other cricket playing nations was that 92% of injuries in the Sri Lankan players occurred during matches, compared to the 52% and 72% reported in elite West Indian and Australian players respectively (Mansingh, et al., 2006; Orchard, et al., 2006). The higher proportion in the Sri Lankan players may be a reflection of the year-round playing schedule of international cricket where very few off-season periods exist, compared to domestic (national level) squads that have a definite off-season and players have greater opportunities to be are involved in prolonged training periods and therefore exposed to training related injuries. Some injury characteristics in these data were similar to other studies, including the 79% of injuries classified as new in the current study, which is similar to the proportion of new injuries reported previously from elite West Indian, Australian and South African cricket squads (Mansingh, et al., 2006; Orchard, et al., 2006; Stretch, 2003; Stretch & Raffan, 2011; Stretch, et al., 2009). Additionally, Orchard et al. (2006) reported an average of 24 injuries per year for the Australian national cricket team and Mansingh et al. (2006) 26 injuries per year for the West Indian cricket, which is similar to the 23.5 injuries per year in the current study. Compared to previous injury surveillance studies, this study found that most injuries occurred during fielding, whereas in the Australian and South African studies, most injuries occurred bowling (Orchard, et al., 2006; Stretch, 2003; Stretch & Raffan, 2011; Stretch, et al., 2009). It is possible that the difference in injury mechanism in the current study may be related to differences in the workloads of fast bowlers, team composition (less reliance on fast bowlers) and differences in playing conditions such 59

61 weather and ground hardness, which may have kept bowling injuries lower than fielding injuries. Match incidence for fielding was also much lower than for batting and bowling, despite most injury injuries occurring whilst fielding. This suggests that fielding injuries occur more in training and that the impact of fielding is diluted once exposure is taken into consideration, as the calculation of match incidence has 11 players exposed while fielding, compared to one player exposed for bowling. The match incidence can be used to compare injury rates between teams and other sports. The 55 injuries per 10,000 player hours in the current study is much lower than rugby which is considered to be a high risk sport but similar to the mean yearly match incidence reported in the New Zealand (W. Frost & Chalmers, 2012), Australian (Orchard, et al., 2006) and West Indies (Mansingh, et al., 2006) international cricket teams. It is however much lower than the 90 injuries per 10,000 player hours reported in the South African international team (Stretch & Raffan, 2011). The Test and ODI match incidence reported by Orchard et al. per year (31 injuries and 60 injuries per 10,000 player hours respectively) and Mansingh et al. (2006) for the West Indies cricket team (49 injuries and 41 injuries per 1000 player hours respectively) showed some similarities similar to the Sri Lankan cricket team (41 injuries for Tests and 70 injuries for ODIs, per 10,000 player hours) and were again considerably lower than the South African team (95 injuries for Tests and 79 injuries for ODIs, per 10,000 player hours) (Stretch & Raffan, 2011). Although similarities existed between teams in some aspects of the match incidence, there were enough differences to support the notion that teams competing in different parts of the world face different challenges when it comes to managing injuries to international teams. 60

62 The seasonal incidence is another good comparison measure between teams and was only reported by Orchard et al. (2006), although they included players competing at both international and domestic cricket tournaments making it difficult to compare with the current study that used international players only. This difference and that the Australian study complied strictly to the international definition, compared to the modified version used in the current study, could explain why the seasonal incidence was less than half of the 10 year mean reported by Orchard et al. (2006) of 16 injuries per squad per season. In particular, injuries in the current study were only included during international duty and may have underestimated the number of injuries per season by excluding injuries that occurred at times when players were involved in domestic competitions. This impact should be relatively small for players competing regularly at international level, as they do not usually have much opportunity to play in domestic competitions. This study was the first to look at injury characteristics from an Indian subcontinent team and where possible used the international definitions for cricket injury surveillance (Orchard, et al., 2005). The main difference in the methods used in the current study, compared to the international consensus, was that players were only included for injury surveillance only when they were selected in the national squad but were not included while they were playing domestic cricket, which may have understated the injury rates. This approach was used because it allowed one person to collect the data; this was a practical decision because of the infrastructure within Sri Lankan cricket at the time of data collection. The other difference was that the method of determining match incidence in the current study varied slightly from the international definition. Orchard et 61

63 al. (2005) recommended the use of standard figures for player hours per team per day, which formed part of the denominator in the match incidence calculation. The standard figures recommended were 39 hours per team per day for match days when 90 overs were scheduled such as Test matches, and 43 hours per team per day when 100 overs were scheduled such as ODIs. To arrive at these figures, Orchard et al. made the assumption that the full number of hours and overs scheduled were actually played. In the current study, we used the actual overs bowled per day to determine the team exposure and we found that figure to be 37 hours per team per day over the two year period, which is lower than the consensus recommendation for both OD and first-class match formats. The method used in this study was likely to be more accurate and therefore should be considered in any future amendment of the cricket injury consensus statements. This study had some limitations. Mainly, the inclusion of players only competing at international level limited the number of participants and therefore the number of injuries available for analysis. Additionally, this resulted in the omission of injury data from domestic games that limited comparison with some previous cricket studies. The injury data was collected for two years; having data for a longer period would have increased the number of injuries available for analysis and been a better representation of the injuries sustained by international cricket players. The inclusion of workload data to the injury analysis would have also enhanced the study. Finally, the study was conducted at a time when Twenty20 cricket matches were not part of the international cricket calendar. This is a form of the game that is an integral part of the modern cricket program making it difficult to compare this study with recent cricket injury surveillance studies. 62

64 2.4 Conclusion This study demonstrated that cricket fast bowlers could be more vulnerable to cricket injury than other players in the squad. In particular, they are more susceptible to injuries such a bone stress injuries that keep players out of the game for long periods of time. The methods used in this study allowed for comparison with previous research and demonstrated that there are some potential differences between teams playing in different parts of the world, particularly the exposure and risk associated with fast bowling and its possible inverse relationship to the amount of bowling workloads carried out by spin bowlers. 63

65 CHAPTER 3: LITERATURE REVIEW OF LUMBAR BONE STRESS INJURIES IN CRICKET FAST BOWLERS Cricket fast bowlers are affected by lumbar bone stress injury at high rates, with the reported incidence over the past 20 years of 11-55%, with most research coming from Australia and England (Engstrom & Walker, 2007; Foster, et al., 1989; Hardcastle, et al., 1992; Ranson, et al., 2010; Ranson, Burnett, King, O'Sullivan, et al., 2008). Chapter 2 provides the first evidence that this is also true for players from the Sri Lanka. The large variation in the incidence of lumbar bone stress injury is largely related to the terminology used to define the injury. Some studies include all radiological features of lumbar bone stress, such sclerosis and old defects (Elliott, et al., 1992; Hardcastle, et al., 1992), without considering symptoms, whilst others only included acute symptomatic bone stress injury (Engstrom, et al., 2007; Ranson, et al., 2010; Ranson, Burnett, King, O'Sullivan, et al., 2008; Stretch, 2003). Additionally, some studies have used radiological investigations retrospectively to identify pars defects (Hardcastle, et al., 1992) or focused on the development of this injury prospectively (Engstrom, et al., 2007; Ranson, Burnett, King, O'Sullivan, et al., 2008). In the previous chapter it was demonstrated that in cricket playing nations, there is universal agreement that lumbar bone stress injuries are associated with long rehabilitation times and result in the most games missed due to injury (Newman, 2003; Orchard, et al., 2002). The long recovery period is consistent with reports of athletes from other sports, with return to pre-injury function ranging from three to twelve months (Jackson, Wiltse, Dingeman, & Hayes, 1981; Letts, Smallman, Afanasiev, & Gouw, 64

66 1986; Morita, Ikata, Katoh, & Miyake, 1995; Ruiz-Cotorro, Balius-Matas, Estruch- Massana, & Vilaro Angulo, 2006; Sys, Michielsen, Bracke, Martens, & Verstreken, 2001). As discussed in the previous chapter, apart from cricket, it is an injury that is common in younger athletes in sports that involve repetitive high axial loading such as gymnastics, soccer and tennis (Gregory, Batt, & Kerslake, 2004; Loud, Micheli, Bristol, Austin, & Gordon, 2007; Ruiz-Cotorro, et al., 2006). Non-surgical management of lumbar bone stress injuries has been shown to successfully restore athletes pre-injury function and allow successful return to sport (Blanda, Bethem, Moats, & Lew, 1993; Congeni, et al., 1997; Miller, Congeni, & Swanson, 2004; Ruiz-Cotorro, et al., 2006; Sairyo, Sakai, & Yasui, 2009; Sakai, Sairyo, Mima, & Yasui, 2010; Sys, et al., 2001). Whilst the majority of athletes do well with conservative management, there are a small number of athletes who have persistent pain and require surgical intervention (Dreyzin & Esses, 1994; Hardcastle, 1993; Mihara, Onari, Cheng, David, & Zdeblick, 2003; Tokuhashi & Matsuzaki, 1996). Whilst there has been a range of published papers from other sports investigating lumbar bone stress injuries such as the assessment, mechanisms, risks and management; there is are very few reviews of literature related specifically to cricket. With this in mind, the aims of this chapter are: 1. Review the literature on the characteristic features of lumbar bone stress injuries in cricket fast bowlers, including the anatomy, epidemiology and pathophysiology, 65

67 2. Review potential risk factors for the development of lumbar bone stress injury in cricket fast bowlers 3. Describe the role of radiological investigations in the identification, management and prevention of lumbar bone stress injuries 4. Describe the key management strategies and timelines associated with lumbar bone stress injuries. 3.1 Terminology The term lumbar bone stress injury will be used in this thesis as an umbrella term for symptomatic stress lesions of the posterior elements of the vertebra including stress reactions and fractures. The most common region of the vertebra susceptible to bone stress is the pars interarticularis (or isthmus) (Leone, Cianfoni, Cerase, Magarelli, & Bonomo, 2011). The common term used to describe these injuries is spondylolysis and can be used interchangeably with the term pars defect to describe both symptomatic and asymptomatic defects (and lysis) in the region of the pars interarticularis. The defect may be a new fracture, a non-united fracture or bone sclerosis. In broad terms, pars defects can be classified as either acute or chronic (Dubousset, 1997). Acute defects are pars lesions that are symptomatic and are active on scintigraphy scanning, have an appearance of a new fracture on computed tomography (CT) scans or demonstrate bone oedema on MRI imaging (Dubousset, 1997). Chronic lesions can be either symptomatic or asymptomatic, but they are not associated with radiological evidence of active pathology on scintigraphy (not active) or MRI imaging (no oedema). The differentiation of acute or chronic change on CT scanning requires an experienced radiologist and is difficult to make. Similarly, 66

68 the terms early and terminal defects are used with similar radiological criteria (Saifuddin & Burnett, 1997; Sairyo et al., 2006; Sakai, et al., 2010). The term lumbar bone stress injury will be the preferred term in this thesis as it refers to symptomatic lesions in the posterior vertebral elements, which can either be stress reactions or stress fractures. The differentiation between stress reactions and fractures is radiological, with stress fractures considered to be further along the bone stress continuum and typically have a visible fracture line on key imaging scans (Brukner, Bennell, & Matheson, 1999). Lumbar bone stress injuries can occur either unilaterally or bilaterally. Bilateral defects can lead to slipping of the vertebra that is referred to as spondylolisthesis (Leone, et al., 2011; Sys, et al., 2001). 3.2 Epidemiology of spondylolysis in fast bowlers Spondylolysis occurs in the general population and is often asymptomatic (Been, et al., 2011; Ko & Lee, 2011). The reported incidence in the general population is 4-9% and varies with race and gender (Been, et al., 2011; Brooks, Southam, Mlady, Logan, & Rosette, 2010; Fredrickson, Baicer, McHolick, Yuan, & Lubicky, 1984; Leone, et al., 2011; Wiltse, Widell, & Jackson, 1975). For example, Caucasian males have a reported incidence of 5-6%, African American men 2-3%, Caucasian women 2%, whilst isolated Eskimos have approximately 60% incidence (Leone, et al., 2011; Wiltse, et al., 1975). In the general population, it more common in men than women and new defects are rare after the onset of adulthood in the absence of repetitive physical activity (Brooks, et al., 2010). 67

69 In the athletic population, lumbar bone stress injuries have been reported in many sporting groups including tennis (Ruiz-Cotorro, et al., 2006), platform or springboard divers (Rossi, 1988), javelin throwers (Schmitt, Brocai, & Carstens, 2001), weightlifters (Rossi, 1988), wrestlers (Rossi, 1988), track and field athletes (Rossi, 1988), volleyball players (Fellander-Tsai & Micheli, 1998), soccer players (Gregory, et al., 2004), ballet dancers (Fehlandt & Micheli, 1993) and gymnasts (Ciullo & Jackson, 1985; McCormack & Athwal, 1999; Rossi, 1988). In young athletic females, bone stress injuries in the lumbar spine are more common than in any other part of the body (Loud, et al., 2007). Loud et al. (2007) reported that 61% of active females who presented with stress fractures at a tertiary care academic children s hospital had fractures of the lumbar pars interarticularis, compared to the 25% of lower limb fractures. The incidence of pars defects (symptomatic and asymptomatic) in cricket fast bowlers reported in the literature varies from 11-55% (Elliott, et al., 1992; Engstrom & Walker, 2007; Foster, et al., 1989; Hardcastle, et al., 1992; Ranson, et al., 2010; Ranson, Burnett, King, O'Sullivan, et al., 2008) and is therefore much higher than the general population (Fredrickson, et al., 1984). It is evident that a problem with interpreting the results of the previous cricket research is that some of the early studies included active stress fractures, chronic pars defects and bone sclerosis together, which may have inflated the figures reported, particularly as some of those included were asymptomatic. Clinically important pars defects are those that are active, symptomatic and need to be confirmed radiologically, such as the stress reactions and stress fractures that are referred to as lumbar bone stress injuries in this thesis. These are lesions are painful, restrict athletic function and keep players out sport for prolong periods of time. One of 68

70 the earliest prospective studies to report the incidence of lumbar spine injury in fast bowlers used CT imaging to demonstrate an 11% incidence of symptomatic lumbar stress fractures in a group of 82 adolescent fast bowlers (Foster, et al., 1989). More recently, Engstrom et al. (2007) prospectively followed a group of adolescent fast bowlers over four consecutive seasons and compared them to age matched controls (swimmers). They reported 23% of bowlers developed symptomatic lumbar stress fractures during the four cricket seasons whilst none of the controls developed serious lumbar spine injury over the same period. Similarly, Ranson et al. (2010) prospectively followed a group of 28 elite English fast bowlers (mean age 19 years) for two years and reported that 54% of bowlers sustained symptomatic and radiologically confirmed lumbar bone stress injury. The highest rate of bony abnormalities of the pars interarticularis (including pedicle sclerosis) in cricket fast bowlers was also reported by Elliott et al. (1992) in a cross-sectional study using one off scans including both CT and MRI. They reported a 55% incidence of spondylolysis, spondylolisthesis and pedicle sclerosis in a group of 20 asymptomatic elite fast bowlers (mean age of 17.9 years). Whilst this study demonstrated a high rate of radiological abnormalities, the association with pain is unknown as players were symptom free at the time of testing. Regardless of the discrepancy in the reported rates of lumbar spine abnormalities, the incidence of pars defects in fast bowlers is much higher than the general population (Elliott, et al., 1992; Engstrom & Walker, 2007; Foster, et al., 1989; Hardcastle, et al., 1992; Ranson, et al., 2010; Ranson, Burnett, King, O'Sullivan, et al., 2008) and similar to the rates reported in other high risk sports such as tennis (Ruiz-Cotorro, et al., 2006), javelin throwing (Schmitt, et al., 2001), gymnastics (d'hemecourt, Zurakowski, Kriemler, & Micheli, 2002; Dixon & Fricker, 1993; Kruse & 69

71 Lemmen, 2009; Loud, et al., 2007), soccer (d'hemecourt, et al., 2002; Fujii, Katoh, Sairyo, Ikata, & Yasui, 2004; Gregory, et al., 2004), basketball (Fujii, et al., 2004), wrestling (Sys, et al., 2001) and diving (Schmitt, et al., 2001; Sys, et al., 2001). The sporting activities with a high incidence of lumbar bone stress injuries have a common mechanism that involves repetitive vertical loading including at least one of trunk sideflexion, rotation or extension that is thought to place stress on the posterior elements of the vertebra. 3.3 Anatomical characteristics of lumbar bone stress injuries There are number of anatomical characteristics that are important in understanding the pathogenesis and clinical presentation of lumbar bone stress injuries. First, it is important to consider the anatomy of the posterior element of the vertebra. Lumbar bone stress injuries in athletes can occur on any part of the posterior element of the vertebra, particularly at the pedicle, lamina or through the facet joints. As discussed earlier, the most common region of bone failure, either as a defect or as bone stress (stress fracture or stress reaction) is the pars interarticularis (Figure 3.1), which is the junction between the facet joints, lamina and pedicle (Bogduk, 1997). The pars interarticularis is a thin portion of the lamina bone with a cross-sectional area of approximately 0.75cm² (Letts, et al., 1986) that lies between the superior and inferior articular processes of the vertebral arch (Brukner, et al., 1999; Engstom et al., 1997). It is situated in a position on the vertebra that has biomechanical importance because it is in the junction between the vertically orientated lamina and the horizontally 70

72 orientated pedicle (Bogduk, 1997). The pars region is therefore placed under stress as bending forces are absorbed where the lamina and pedicle intersect (Bogduk, 1997). The pars interarticularis also functions as a fulcrum for the posteriorly located facet joints that are important in preventing excessive motion of the lumbar spine (Engstom, et al., 1997). It is therefore expected that any spine positions that result in forces transmitted to the facet joints will also be absorbed through the adjacent pars interarticularis. Figure 3.1 Sagittal CT scan of the pars interarticularis (circled area) Bone geometry is also important when considering lumbar bone stress injuries. Whilst most of the vertebra is made of porous trabecular bone, the lamina (and pars interarticularis) is made of the more dense cortical bone, which is more capable of withstanding tensile and compressive forces of vertical loading (Letts, et al., 1986). Bone geometry is proportionally related to bone strength (Brukner, et al., 1999) and the pars 71

73 interarticularis has a geometry that emphasises its role as force dissipater (Bogduk, 1997). Cortical bone is more capable of withstanding high forces but does have a lower metabolic activity than trabeculae bone and is therefore less capable of responding to changes in mechanical load than trabeculae bone (Brukner, et al., 1999). In cricket fast bowling, transmission of high vertical forces through the pars interarticularis occurs mainly at front-foot impact during the delivery stride (Elliott, et al., 1986; Ferdinands, et al., 2009; Portus, 2001). The high rates of bone sclerosis on imaging at the pars interarticularis in cricket fast bowlers (Hardcastle, et al., 1992) is evidence of the bone production from mechanical loading and a possible bone strengthening mechanism to prevent stress fractures. It is likely that the limited metabolic response of cortical bone limits adaptation to mechanical load, and has some role in the development of the stress response at the pars interarticularis. In fast bowling, the mechanical load at the pars interarticularis is likely to come from the combination of trunk extension and ipsilateral trunk side flexion and rotation. This combination of trunk positions have been recently termed as the crunch factor and are thought to lead to the stress required to cause injury in fast bowlers (Glazier, 2010). Evidence that this crunch position is an important factor in the development of lumbar bone stress injuries is the consistent nature of the asymmetrical distribution of this injury in fast bowlers, with the overwhelming majority of bone abnormalities occurring on the opposite side of the bowling-arm (Elliott, 2000; Gregory, et al., 2004; Hardcastle, et al., 1992; Portus, et al., 2004; Ranson, 2010). This is further highlighted when cricket bowling is compared to other sports with more symmetrical spinal loading patterns such 72

74 as soccer (Gregory, et al., 2004) that have a more even distribution of lumbar bone stress injuries between the dominant and non-dominant sides. A common anatomical characteristic in cricket fast bowlers that is consistent with other sports, is that lumbar bone stress injuries occur more commonly at the lower two lumbar vertebrae (Blanda, et al., 1993; d'hemecourt, et al., 2002; Elliott, et al., 1992; Engstrom & Walker, 2007; Foster, et al., 1989; Gregory, et al., 2004; Hardcastle, et al., 1992; Leone, et al., 2011; Morita, et al., 1995; Ranson, et al., 2010; Rossi, 1988; Sairyo, et al., 2006). Most athletic bone stress injuries occur at the L5 vertebral level (d'hemecourt, et al., 2002; Fujii, et al., 2004; Miller, et al., 2004; Sakai, et al., 2010; van der Wall et al., 2002). Studies of recreational athletes highlight the L5 bias for pars defects. Fuji et al. (2004) described symptomatic spondylolysis in a physically active adolescent population, with 85% of the bone defects located on the L5 vertebra and 15% at L4 vertebra (Fujii, et al., 2004). Similarly, de Hemecourt et al. (2002) reported that 62% of physically active adolescents and young adults (n=75) had symptomatic L5 spondylolysis. In other elite athletes, tennis players have a reported 80% of the symptomatic lumbar bone stress lesions occurring at L5 and 12% at L4 (Ruiz-Cotorro, et al., 2006). Similarly, elite level javelin throwers, who to have similar mechanics to cricket fast bowlers, have been shown to have higher rates of L5 pars defects compared to other levels (Schmitt, et al., 2001). In cricket, previous studies have demonstrated that fast bowlers have a pattern of pars defects, or lumbar bone stress, located most commonly on the L5 level. Hardcastle et al. (1992) and Foster et al (1989) reported that 83% and 77% of pars defects (respectively) were located on the L5 vertebra in fast bowlers. Gregory et al. (2004) also reported a higher distribution of L5 (39%) compared to L4 73

75 (22%) symptomatic bone stress injuries in fast bowlers. Others have found higher distribution of L4 vertebral injuries with Ranson et al. (2010) reporting an equal distribution between L5 and L4 bone stress lesions in symptomatic fast bowlers, whilst Engstrom et al. (2007) reported an unusually higher (92%) distribution of bone stress injuries in adolescent cricket fast bowlers at the L4 vertebral level. It is possible that the L5 vertebra is the most vulnerable to pars defects, with the L4 vertebra being placed under load with certain bowling techniques or possibly related to the age of the players. 3.4 Why is the L5 vertebra most vulnerable to bone stress injury? There are a variety of factors that may explain why the L5 vertebra is vulnerable to bone stress. It has been proposed that greater forces are placed on the L5 vertebrae, compared to other vertebrae, with some spine positions, particularly lumbar extension (Annear, Chakera, Foster, & Hardcastle, 1992; Ebraheim, Lu, Hao, Biyani, & Yeasting, 1997; Elliott, 2000). It is also structurally different to other vertebrae, which may predispose it to higher rates of par defects (Ebraheim, et al., 1997). In particular, L5 is at a junction where there is an abrupt change of direction between the lordotic spinal column and the kyphotic sacrum, which may increase stress across the posterior vertebral elements (Elliott, 2000). Additionally, the L5 vertebra may be more vulnerable to high shear forces than other spinal levels because it is transition point between the rigid sacrum and the relatively mobile lumbar spine (Annear, et al., 1992). It is also subjected to the largest forces of all the lumbar vertebra when the spine is hyperextended (Ebraheim, et al., 1997), a position that commonly occurs in sporting activities that are 74

76 considered to be high risk (d'hemecourt, et al., 2002; Miller, et al., 2004) and in particular with cricket fast bowling (Portus, 2001). Histologically the pars interarticularis region is different at the L5 vertebra than other lumbar vertebrae, which could also make it more vulnerable to lumbar bone stress injuries (Ebraheim, et al., 1997; Sagi, Jarvis, & Uhthoff, 1998). In particular the superoinferior diameter of the pars interarticularis is relatively smaller in the lower lumbar vertebrae, especially the L5 vertebra, and therefore weaker than the pars of the upper lumbar vertebrae (Ebraheim, et al., 1997). The medial and caudal inclination of the isthmus was greatest at L5 and it was thought to predispose it to larger shear forces from axial loading (Ebraheim, et al., 1997). Additionally, the pars interarticularis of L5 undergoes changes during fetal development that differentiate it from the upper lumbar vertebrae, that possibly make it less capable to withstand high forces (Sagi, et al., 1998). It is likely that the combination of the factors described above predispose the pars interarticularis region of the L5 vertebra to greater risk of a defect with vertical loading. Sporting activities that involve spine extension, side-flexion and rotation are likely to provide the excessive load required to develop a pars defect at any vertebral level but with the L5 being the most vulnerable. 3.5 Pathogenesis of lumbar bone stress injuries To understand the pathogenesis of stress fractures it is important to review the basics of bone physiology and its response to physical activity. Bone is a dynamic structure that responds to physical loading through two key processes; modeling and 75

77 remodeling (Burr et al., 1989; H. Frost, 1997). Central to these processes are bone cells (osteoclasts, osteoblasts and osteocytes) (H. Frost, 1997). Bone modeling is a process that involves the addition of bone, occurring predominantly during developmental years, which increases bone strength and mass (H. Frost, 1997). For this reason increased bone mass is rare after skeletal maturity (Burr, et al., 1989). Bone remodeling is a process of bone turnover so that damaged bone cells are resorbed and replaced by new bone cells. Unlike bone modeling, remodeling involves the coupling of osteoblasts and osteoclasts. It is a process that is ongoing throughout life, which conserves existing bone in early adulthood and results in bone reduction after middle age (H. Frost, 1997). Both modeling and remodeling can be turned on or off by the preset thresholds of bone strain (H. Frost, 1997). The threshold for bone strain is an important gauge because it controls the bone modeling and remodeling process that gives bone the strength required to withstand the bone deformation forces associated with physical activity. The forces required to deform bone and stimulate these responses are from two different sources: muscle contractions and axial loading through gravitational forces. During growing years, modeling is required to strengthen bone so that it can cope with the increased deformation forces that result from increasing lever arms as bones lengthen longitudinally; and to withstand the higher forces generated from increased muscle contraction that occur during development (Rauch & Schoenau, 2001). Once skeletal maturity is reached, bone continues to respond to forces from muscle contractions and axial loading through the remodeling process to maintain bone strength and mass (Rauch & Schoenau, 2001). 76

78 Physical activity provides the bone stress that is important in the development of normal bone by stimulating the modeling and remodeling processes, which in turn allows bone to develop the strength needed to cope with the forces that it is exposed to (Brukner, et al., 1999). Physical activity increases the forces (deformation strain) acting on bone through muscle contractions and gravitational loading resulting in increased bone mass. The increase in bone mass that results from exercise is site specific and the extent of the response is related to the amount of activity, as evidenced by elite athletes demonstrating the large osteogenic response to regular loading (Bass et al., 1998; Huddleston, Rockwell, Klund, & Harrison, 1980). For example, elite gymnasts have greater bone mass in weight bearing bones when compared to age matched controls (Bass, et al., 1998), whilst elite tennis players have greater bone mass on the dominant arm, when compared to the nondominant arm (Huddleston, et al., 1980). The extent of the exercise related osteogenic response also varies with age, with the greatest response occurring in the pre-pubescent years (Bass, et al., 1998). The osteogenic response seen in the pre-pubescent elite athletes can result in higher long term peak bone mass and is thought to be a protective mechanism for osteoporosis later in life (Bass, et al., 1998). The changes in bone geometry through the osteogenic response to deformation forces are an important protective mechanism, particularly when the stress is repetitive and there is inadequate time for bone remodeling to occur. The osteogenic response is stimulated when the bone stress from physical activity is greater than what the bone is normally accustomed to (bone strain threshold). Exceeding the bone strain threshold, results in small micro-fractures within the bone structure that initiates the remodeling process to repair the damage. If there is insufficient time to remodel bone before the next 77

79 loading cycle, the micro-fractures ultimately become defects and eventually symptomatic stress reactions or fractures (Brukner, et al., 1999; Sys, et al., 2001). The number of loading cycles required to initiate a stress fracture is related to the bone s strength and geometry, as well as the magnitude and frequency of loading applied (Crossley, Bennell, Wrigley, & Oakes, 1999). In running athletes, smaller CSA of the tibia differentiated athletes with a previous history of tibial stress fracture and those no previous stress fractures, highlighting the role of bone geometry in stress fracture development (Crossley, et al., 1999). 3.6 Mechanism for bone stress at the lumbar pars interarticularis in fast bowlers Pars defects were initially thought to be congenital, however numerous studies have demonstrated that they are most likely developed in early childhood, after the age of 5 years and before the skeletal system is full developed in adulthood (Leone, et al., 2011; Letts, et al., 1986). In particular an examination of spines at birth has shown a zero incidence of pars defects as would be expected if congenital (Ebraheim, et al., 1997). There is an increase in incidence of pars defects between childhood and adulthood, which would not be possible if they were totally congenital and not associated with development. In particular, children between 5-6 years of age have an approximate 5% prevalence of lumbar pars defects that rises to approximately 6% by early adulthood (Wiltse, et al., 1975), whilst the frequency of pars defects in the general population remains relatively constant after 20 years of age (Brooks, et al., 2010; Letts, et al., 1986). Additionally, pars defects are not present in the non-ambulatory population, which further suggests that they are associated with the vertical loading that comes with upright 78

80 posture (Letts, et al., 1986). Perhaps the most compelling case against the congenital theory is that pars defects are capable of achieving osseous healing, which would not be possible they were congenital lesions (Morita, et al., 1995; Sakai, et al., 2010; Sys, et al., 2001). Finally, as discussed previously, some sporting activities are associated with higher incidence of pars defects and bone stress injuries than reported in the general population, which is indicative that repetitive loading is likely to be associated with the development of the bone abnormalities (Leone, et al., 2011). The sporting activities with the highest rates of lumbar pars defects and bone stress injuries are typically associated with high repetitive vertical forces through the lumbar spine, which is considered to be an important component in the development of this injury (Leone, et al., 2011). In particular, it is likely that activities involving repetitive trunk extension, side flexion and rotation, place the greatest load through the posterior elements of the vertebra leading to bending and weakening of the vertebral arch and ultimately creating a defect or bone stress injury in the vulnerable pars region (Foster, et al., 1989; Kruse & Lemmen, 2009; Letts, et al., 1986; Lonstein, 1999; Portus, et al., 2004; Ranson, Burnett, King, O'Sullivan, et al., 2008). It is proposed that the stress from these trunk movements results in localised wedging of the pars interarticularis between the inferior articular process of the vertebra above and the superior articular process below (Leone, et al., 2011). As discussed earlier, Glazier et al. (2010) described combination trunk extension, contralateral side flexion and ipsilateral rotation that occurs at front-foot impact during the fast bowling delivery as the crunch factor and proposed that is was responsible for the tensile and compressive forces on the pars interarticularis. This supports that the pathogenesis of lumbar bone stress injury is most likely to be 79

81 through repetitive high loading resulting in bone micro-trauma and ultimately stress fracture, as opposed to a single episode of macro-trauma (d'hemecourt, et al., 2002; Leone, et al., 2011). Injury surveillance data from Australian cricket supports this the micro-trauma theory as 94% fast bowlers diagnosed with symptomatic lumbar stress fractures reported a gradual onset of pain over a prolonged period of time rather than single event (Orchard, 2008). Engstrom et al. (2007) proposed an alternative mechanism where the contralateral (to the bowling-arm) QL muscle produced an increase in shearing forces at the pars interarticularis during the repetitive contraction during the lumbar spine side flexion. This hypothesis arose from their findings that the adolescent fast bowlers with the largest QL asymmetries (ipsilateral side larger) were more likely to sustain lumbar stress fractures (Engstrom, et al., 2007). This hypothesis has not been rigorously tested and remains a less likely mechanism of bone stress, especially as others have not found a relationship between lumbar stress fractures and QL asymmetry in cricket fast bowlers (Ranson, Burnett, King, O'Sullivan, et al., 2008). 3.7 Pars defects and pain As discussed earlier in this chapter, it is painful pars defects that are clinically relevant in the sporting environment. These can either be acute bone stress injuries or an existing defect that becomes painful because of a sporting activity. The pars interarticularis has free nerve endings with nociceptive functions capable of being a direct source of pain (Schneiderman, McLain, Hambly, & Nielsen, 1995). In the general 80

82 population, pars defects are commonly asymptomatic (Brooks, et al., 2010), most likely because there is mature scar tissue (fibrous or cartilaginous) that fills the defect (Leone, et al., 2011). In the sporting population, including cricket fast bowlers, the defects can also be asymptomatic (Hardcastle, et al., 1992; Millson, Gray, Stretch, & Lambert, 2004) but are more likely to be painful, possibly because the repetitive loading of the posterior elements of the vertebra result in an acute bone injury or disruption of the scar within the existing defect. It is these painful lesions that limit athletic participation that have been the focus of most research and are most clinically relevant (Elliott, et al., 1992; Engstrom & Walker, 2007; Hardcastle, 1991; Micheli, Hall, & Miller, 1980; Ranson, Burnett, King, O'Sullivan, et al., 2008; Rossi, 1988; Ruiz-Cotorro, et al., 2006; Sys, et al., 2001). In cricket fast bowlers, acute bone marrow oedema (MRI) and increased bone uptake (scintigraphy) in the region of the pars interarticularis have been associated with low back pain confirming that the pars interarticularis can be a pain site (Engstrom, et al., 2007; Foster, et al., 1989; Gregory, et al., 2004; Gregory, Batt, Kerslake, & Webb, 2005; Ranson, et al., 2010; Ranson, Burnett, King, O'Sullivan, et al., 2008). Earlier studies that used x-ray and CT scan, which are less sensitive radiological techniques of picking up bone stress injuries, and have also have demonstrated a high correlation between radiological pathology and lower back pain in fast-bowlers (Annear, et al., 1992; Elliott, et al., 1992; Hardcastle, et al., 1992). Elliott et al. (1992) demonstrated that 73% of young fast bowlers with abnormal radiological features at the pars interarticularis also had complained of back pain during that season. Similarly, Hardcastle et al. (1992) who reported that 92% of adolescent fast bowlers with radiological evidence of pars defects had pain with bowling, with almost half of this group having to stop bowling due to the 81

83 pain during the next cricket season. Ranson et al. (2005) performed MRI on 38 asymptomatic elite level fast bowlers and reported 22% of the cohort had signs of acute bone stress with bone oedema in the area of the pars interarticularis. The same group also showed that 70% of asymptomatic bowlers with bone oedema on MR imaging at the start of a cricket season went on to develop symptomatic lumbar stress fractures of the pars interarticularis during the next cricket season (Ranson, Burnett, King, O'Sullivan, et al., 2008). The have been some cricket studies that have demonstrated that radiological evidence of pars pathology in the absence of pain. These studies have mainly used imaging techniques that cannot distinguish between acute (active) and chronic (nonactive) lesions, such as CT and x-ray; or were cross-sectional studies performed at start or end of a cricket season that did prospectively record the development of clinical symptoms (Elliott, et al., 1992; Hardcastle, et al., 1992; Millson, et al., 2004; Ranson, et al., 2005). One such study demonstrated dissociation between the appearance of pars defects on CT imaging and low back pain in 10 young fast bowlers and concluded that CT imaging alone was not an optimal method of determining symptomatic bone lesions in the lumbar spine (Millson, et al., 2004). These studies highlight that the importance of using appropriate imaging techniques when lumbar bone stress injury is suspected and correct study designs when investigating this injury. In clinical practice, a combination of radiological investigations and clinical skills determine if the low back pain experienced by patients is due to spondylolysis or other structures. This multifactorial approach is also required in research studies to determine 82

84 whether pars defects are symptomatic or asymptomatic lesions or if the pain originates from another structure. 3.8 Sclerosis Cyclic loading of bone leads to increased bone mineral density through the process of micro-damage and repair that results in bone thickening (Marquiles et al., 1986). This is considered to be a protective mechanism and a sign that bone is under localised load. Studies on the lower limbs of military recruits have demonstrated that four weeks of training leads to one of two outcomes; either significant increases in bone mineral content and thickening of the bone (sclerosis) or a stress fracture (Marquiles, et al., 1986). It appears that it is a fine line between bone remodeling and stress fracture. In cricket fast bowlers, sclerosis of the pedicle is a common radiological finding and is thought to be representative of increased bone density of the pars interarticularis region and confirming the localised bone stress associated with the bowling technique (Elliott, et al., 1992; Walker, Engstom, Wallace, & Kippers, 1995). The sclerotic appearance of the pars interarticularis has been described as a sign of a developing or healing fracture (Elliott, Davis, Khangure, Hardcastle, & Foster, 1993). It is a likely result of either bone stress that results in bone remodeling prior to the development of a stress fracture or excessive (hypertrophic) bone formation in the healing phase after stress fracture. Pedicle sclerosis has been demonstrated radiologically in fast bowlers using CT (Elliott, et al., 1992; Foster, et al., 1989; Gregory, et al., 2005), MRI (Engstom, et al., 1997; Walker, et al., 1995) and plain x-ray (Annear, et al., 1992). Walker et al. (1995) 83

85 demonstrated that sclerosis was present in 92% of elite fast bowlers (aged years) on the opposite side to bowling-arm, whereas control participants in the study had no sclerosis (Walker, et al., 1995). Gregory et al. (2005) also reported that sclerosis was common finding in young athletes who had lower back pain and radiological evidence of a stress reaction at the pars interarticularis. Elliott et al. (1992) used CT to demonstrate that pedicle sclerosis was the most common radiological abnormality detected in a group of young fast bowlers, as 73% of them developed pain in the following season. Whilst the exact role of sclerosis in the clinical paradigm of lumbar bone stress is unknown, the results from these studies suggest that, sclerosis is likely to be part of the development phase of spondylolysis and therefore a clinically relevant finding. 3.9 Disc degeneration, fast bowling and pars defects Lumbar intervertebral disc degeneration is a common finding in patients with spondylolysis (Dai, 2000). In the asymptomatic general population there were differences in lumbar disc geometry between individuals who had radiological evidence of spondylolysis and those without spondylolysis (Been, et al., 2011). The lumbar intervertebral disc is placed under considerable stress during fast bowling as the spine performs twisting and bending movements (Elliott, et al., 1993) whilst forces of between six to nine times bodyweight are absorbed at front-foot impact (Elliott, et al., 1992; Foster, et al., 1989). Walker et al. (1995) reported a higher but non-significant occurrence of degenerative disc pathology in cricket fast bowlers (77%) when compared to physically active controls (50%). They also found an increase in the number of end-plate deformities in fast bowlers compared to controls especially in the upper lumbar spine and 84

86 thoraco-lumbar junction (Walker, et al., 1995). A more recent study demonstrated that 35% of asymptomatic adolescent fast bowlers had MRI evidence of disc degeneration (Crewe, Elliot, Couanis, Campbell, & Alderson, 2012), whilst Ranson et al. (2005) also demonstrated that asymptomatic adult fast bowlers had high rates (61% of cohort) of disc pathology, although this was only slightly higher than the rate in age matched controls (53% of cohort). However, in the Ranson et al. study, fast bowlers did have a high proportion of discs categorised as severely degenerative (33%) compared to the controls (12%) suggesting a more accelerated degenerative process with fast bowling. Although disc pathology is not considered as serious as spondylolysis in young fast bowlers (Elliott, et al., 1992) it can still cause significant pain and dysfunction (Elliott, et al., 1993; Elliott, et al., 1992; Hardcastle, et al., 1992). Elliott et al. (1993) used MRI to demonstrate that bowlers as young as 13 years of age who adopted a bowling technique that was considered less safe (mixed bowling action) had an increased incidence of disc pathology than those who used safer techniques (front-on or side-on techniques) (Elliott, et al., 1993). Hardcastle et al. (1992) reported that 64% of young fast bowlers had disc degeneration evident on MRI with a majority of these (78%) also reporting pain with bowling. An interesting finding in this study was that more than half of the group also had radiological evidence of pars defects, which may also explain the pain but importantly highlights the possible link between disc pathology and pars defects. Hardcastle et al. (1992) also demonstrated a high rate of disc degeneration in young fastbowlers with approximately half of the bowlers with disc degeneration also having associated pars defects. Ranson et al. (2005) also investigated the link between disc pathology and pars defects but found no relationship between disc degeneration and pars 85

87 interarticularis defects (acute or chronic). They did however find that all fast bowlers with chronic pars defects also had severe disc degeneration, whilst only 50% of the controls with chronic defects had similar degree of disc degeneration. This suggests a possible relationship between disc pathology and pars defects but the nature of this relationship is unknown. It is possible that disc degeneration leads to an increase in compression forces transmitted through the facet joints and ultimately the pars interarticularis leading to spondylolysis. Alternatively, the same mechanisms that result in spondylolysis may also lead to disc degeneration. For instance, Elliot et al. (1993) found that bowlers with the mixed bowling technique were more likely to result have thoraco-lumbar disc degeneration. This same technique has also been linked to the development of spondylolysis in cricket fast bowlers (Foster, et al., 1989; Portus, 2001; Portus, et al., 2004). This relationship between disc degeneration and lumbar bone stress injuries was not found in the most recent study to investigate this in fast bowlers. Ranson et al. (2010) reported a high rate of lumbar disc degeneration on MR imaging in their group of elite fast bowlers (mean age 19 years) but found no significant correlation between disc degeneration and lumbar bone stress or stress fractures Risk factors in the development of lumbar bone stress injury in fast bowlers No single risk factor has been identified in the development of lumbar bone stress injury in cricket fast bowlers (Johnson, Ferreira, & Hush, 2012). It likely that a combination of intrinsic and extrinsic factors is required to exceed the bone tensile 86

88 strength that leads to lumbar bone stress injury. In particular, when and where bones fail during the bone stress continuum are determined by the frequency and magnitude of bone loading compared to the bones strength (Bennell et al., 2004; Brukner, et al., 1999). As there are a limited number of studies investigating risk factors of lumbar bone stress injuries in cricket fast bowlers, the following section examines factors identified in cricket and other high risk sports. Age The exact relationship between age and lumbar bone stress injury is unknown but it is generally accepted that it is common amongst younger athletes, mainly because most of the published research related to lumbar bone stress injuries has involved adolescent and younger athletes ranging from years of age (Campbell, et al., 2005; d'hemecourt, et al., 2002; Engstrom, et al., 2007; Foster, et al., 1989; Hardcastle, et al., 1992; Masci et al., 2006; Milgrom et al., 1994; Miller, et al., 2004; Morita, et al., 1995; Ruiz-Cotorro, et al., 2006; Stretch, 2003). Whilst there is no hard evidence that younger athletes are at risk to develop bone stress injury, younger age has been related to increased risk of other stress fractures in military recruits (Milgrom, et al., 1994). More specifically to the lumbar spine, Masci et al. (2006) investigated 71 physically active participants, aged years, that presented at sports medicine clinics with suspected active lumbar bone stress injury. They reported that all of the participants with confirmed active bone pathology, using scintigraphy, were under the age of 25 years. In cricket, it is an injury that is also commonly reported in younger fast bowlers (Engstrom, et al., 2007; Foster, et al., 1989; Hardcastle, et al., 1992; Ranson, et al., 2010; 87

89 Ranson, Burnett, King, O'Sullivan, et al., 2008). Lumbar bone (radiological) abnormalities as high as 54% have been demonstrated in young (16-18 years) cricket fast bowlers (Hardcastle, et al., 1992). Engstrom et al. (2007) reported that 23% of adolescent fast bowlers, aged between 13 to 17 years of age, sustained symptomatic lumbar spine stress fractures over a four year period. Studies that have involved adult cricket players also demonstrated that younger bowlers having higher rates of lumbar spine injury. Ranson et al. (2008) reported that 25% of elite adult fast bowlers sustained lumbar bone stress injuries over one cricket season but mean age was 22 years. The same group also reported that 43% of elite fast bowlers who developed lumbar bone stress injuries had a mean age of 19 (16-24) years over a two year period (Ranson, et al., 2010), whilst the mean age of fast bowlers with lumbar stress fractures reported by Gregory et al. (2004) was 19.7 years (range years). These studies highlight that bowlers may be more vulnerable to lumbar bone stress injury before the age of 25 years. This age group also featured in the South African injury surveillance study, as Stretch (2003) reported all fast bowlers who developed lumbar bone stress injuries during their three year injury surveillance of elite South African cricket players were under the age of 24 years, again highlighting the vulnerability of younger athletes to this injury. It is proposed that lumbar bone stress injury is common in adolescent or younger athletes because their immature skeletal system has a lower tolerance to repetitive high loading and lower threshold for fracture (Elliott, et al., 1993). It is therefore likely that lumbar bone stress injury occurs when a developmentally weaker neural arch is subjected to repeated loads that exceed its strain limit; a limit that is thought to be lower than in fully matured vertebra. This theory fits in with the developmental pathway of bone, 88

90 particularly the lumbar vertebra, which has three primary ossification centres (Prakash et al., 2007). One ossification centre, the centrum develops into a large portion of the vertebral body. The other two ossification centres occur at the vertebral arches and join together to create the completed vertebral arch and the posterior part of the vertebral body. Ossification of the primary centres begins in fetal life and fuse by the age of three (Wang et al., 2001). By the age of six years, the ossification centre at the centrum fuse with the vertebral arch, known as the neurocentral synchondroses (Gray, 1918). The lumbar spine is not fully ossified until years of age (Walsh, Henry, Fatayerji, & Eastell, 2009) and therefore fits in with the age group discussed earlier, that seem to be most vulnerable to lumbar bone stress injuries. It is possible that incomplete closure of the ossification centres at neural arches may predispose adolescents to this injury. Additionally, bone mineral content (BMC) and bone mineral density (BMD), which are both determinants of bone strength, increase proportionally at the lumbar vertebrae between years of age and are influenced by puberty (Kroger, et al., 1993; Kroger, et al., 1992). The age of fast bowlers who develop this injury fits into this developmental period and may be another important factor in the development lumbar bone stress injury in adolescent and younger athletes. Finally, bone development is site specific and can be influenced by stress associated with certain physical activities (Kroger, et al., 1993). In the lumbar spine, important geometric parameters that influence bone strength continue to develop with age until the mid-twenties. In skeletal system, the majority of increases in BMD and BMC occur between puberty and 18 years of age but in the lumbar spine there are increases in BMD, BMC, vertebral height and vertebral width until 25 years of age (Walsh, et al., 2009). This age (25 years) seems to be an important time in the 89

91 development of lumbar bone stress injuries because this injury is rarely reported beyond this age and is about the time that peak bone strength is achieved (Walsh, et al., 2009). Another possible factor that predisposes young fast bowlers to lumbar bone stress injuries a relatively elastic intervertebral disc that allows intervertebral shear forces to reach the facet joints, placing excessive stress on osseous structures (Cyron & Hutton, 1978). These extra forces on the pars interarticularis, coupled with the immature neural arch that has not undergone complete ossification, are likely to be why young fast bowlers are predominantly affected by this injury. Finally, it is also possible that younger bowlers are at greater risk of lumbar bone stress injuries because they lack the repetitive loading (through bowling) that comes with increased years in a sport, and serves as a protective factor from bone stress through some other pathway such as improved muscle strength or control. In cricket, there are no definitive studies demonstrating the protective or harmful influence of previous bowling load. Dennis et al. (2004) demonstrated that bowling too frequently or too infrequently were both factors associated with lumbar spine injury in adolescent fast bowlers. It is possible that there is a balance between bone development and graded repetitive loading through fast bowling that may be protective from bone stress injury during adolescence. Bowling biomechanics and trunk positions As discussed earlier in this chapter, fast bowling has been associated with lumbar spine injuries because the trunk is rotated, laterally flexed and extended over a short period of time during the delivery stride, whilst absorbing high impact forces, particularly at front-foot impact (Elliott, et al., 1992; Foster, et al., 1989; Glazier, 2010). Whilst it is 90

92 still unclear whether one particular position of the spine causes stress on the lumbar pars interarticularis region in fast bowlers or if it is related to combination of positions, fast bowling is an unnatural activity that involves trunk positions that are not typically experienced during daily activity. Some of the earlier cricket related studies have proposed that lumbar extension and rotation during the delivery stride are most likely to associated with lumbar bone stress injury (Elliott, et al., 1992; Hardcastle, et al., 1992). This theory is supported by a cadaver study that has shown that the pars interarticularis is placed under high stress when the spine is in a hyperextended position and this stress can cause bone failure leading to spondylolysis (Green, Allvey, & Adams, 1994). Subsequently, the role of lumbar side flexion in the bowling technique has also received some attention. Burnett et al. (1998) highlighted the importance of extension and but also suggested that contralateral side flexion may also play an important part in injury mechanism. More recently, Ranson et al. (2008) proposed that the amount of contralateral side flexion and ipsilateral rotation at front-foot impact were important factors in the development of lumbar spine injury in cricket fast bowlers. They found that the greatest range of motion in the lower lumbar spine at front-foot impact was contralateral lumbar side flexion and not lumbar extension. They concluded that the combination of high rates of contralateral side flexion, ipsilateral rotation and the large impact forces would be most likely to be associated with pars interarticularis bone stress (Ranson, Burnett, King, Patel, et al., 2008). It is possible that a combination of trunk position are responsible for the high force required to develop lumbar bone stress injuries and fits in with the concept of the crunch factor introduced by Glazier (2010) earlier in this chapter. 91

93 Fast bowling technique There are four main bowling techniques that have been identified and are described in detail in Appendix D. While fast bowling involves an unnatural combination and range of trunk positions that stress the posterior elements of the vertebra, not every bowler sustains a lumbar bone stress injury. It is proposed that certain bowling techniques increase the stress on the lumbar spine and predispose bowlers to injury, which is supported research associated certain fast bowling techniques and lumbar spine injuries (Burnett et al., 1996; Elliott, 2000; Elliott, et al., 1993; Elliott, et al., 1992; Foster, et al., 1989; Hardcastle, et al., 1992; Portus, et al., 2004). See Appendix D for a description of the different bowling techniques. The early studies linked the mixed technique with a greater risk of lumbar spine injury in fast bowlers, because bowlers who used the mixed bowling action had higher rates of pars defects and other abnormal radiological findings in the lumbar spine (A. Burnett et al., 1996; Elliott, 2000; Elliott, et al., 1993; Elliott, et al., 1992; Foster, et al., 1989; Hardcastle, et al., 1992; Portus, et al., 2004). Portus et al. (2004) demonstrated a greater separation angle between the pelvis and shoulders at backfoot impact (a characteristic of the mixed technique) in bowlers with a history of lumbar stress fractures. The mixed technique also typically involves higher rates of trunk contralateral side flexion and hyperextension during delivery stride, than other bowling actions and therefore places greater stress through the posterior vertebral elements (A. Burnett, Barret, Marshall, Elliot, & Day, 1998). Another technical aspect that has been associated with lumbar bone stress injuries is shoulder counter-rotation (SCR), which is also closely associated with the mixed bowling technique. More specifically, bowlers with higher rates (greater than 30º) of 92

94 SCR during the delivery stride have been associated with significantly higher incidence of lumbar spine stress injuries and abnormal radiological features (Elliott, et al., 1993; Elliott, et al., 1992; Foster, et al., 1989; Portus, 2001; Portus, et al., 2004). Refer Appendix D for a description of SCR. As discussed earlier, the interrelationship between trunk lateral flexion, extension and rotation during the delivery stride, places stress through the posterior elements of the vertebra. Whether these aspects of the bowling technique affect adolescent and adult bowlers differently is unknown. It is possible that older bowlers can tolerate greater extremes of range compared to younger bowlers because of the expected musculoskeletal adaptions of the chronic bowling workloads or more mature bone development. If this is case, it is important that young fast bowlers have regular biomechanical screening of their technique in order to minimise any inefficient and harmful technique components. Bowling workloads Like any bone stress injury, lumbar spine pars injuries are overuse injuries and require a repetitive loading before bone failure (Brukner, et al., 1999). The amount of repetitive load required to cause bone stress will be dependent on a number of interrelated factors, but repetitive loading that occurs during the delivery stride is likely to be key factor. Bone stress and ultimately fracture is thought to occur when insufficient time is given between loading sessions for the bone to adapt and repair (Bennell, et al., 2004). In cricket, bowling workloads in a single session, in a match or over a cricket season, have been associated with injuries in fast bowlers (A. Burnett, Elliot, & Marshall, 1995; Dennis, Farhart, Goumas, & Orchard, 2002; Foster, et al., 1989; Portus, Sinclair, Burke, 93

95 Moore, & Farhart, 2000). Amongst these studies, only Foster et al. (1989) specifically looked at the relationship between workload and lumbar bone stress injuries. They followed 82 young fast bowlers over a cricket season and found that of the 32 bowlers who bowled more than the mean number of 17 games in a season, 59% sustained stress fractures of the pars interarticularis or other injuries to the lumbar spine. Whilst, this is not comprehensive evidence that the repeated loading from bowling is related to bone stress injuries, it does highlight the possible relationship. Burnett et al. (1995) and Portus et al. (2000) both demonstrated that bowling a single prolonged bowling spell can affect bowling mechanics with the main impact being an increase in the amount of SCR. As discussed earlier, excessive SCR during the delivery stride been associated with lumbar bone stress injuries (Elliott, et al., 1993; Elliott, et al., 1992; Foster, et al., 1989; Portus, 2001; Portus, et al., 2004) making it likely that the altered mechanics that result from a prolonged bowling session may predispose bowlers to lumbar bone stress injury. A recent landmark study has highlighted the relationship between high bowling workloads, particularly bowling spikes, and lumbar spine injury in cricket fast bowlers. Orchard et al. (2009) investigated the link between acute heavy bowling workloads ( spikes ) and injury in elite level adult fast bowlers. They demonstrated that bowling more than 300 deliveries in single match or 180 deliveries in the second innings of a match increased the risk of any injury in the weeks following the match. Interestingly, it was the day period after the spike when injuries were most likely to occur. This study involved injury data from a comprehensive injury surveillance program and included all fast bowling injuries, not just lumbar bone stress injuries. However, lumbar 94

96 bone stress injuries made up 7% of all fast bowling injuries during the surveillance period but 13% of injuries that were related to the workload spikes (Orchard, James, Kountouris, & Portus, 2009). This suggests that lumbar bone stress injuries were over represented in the injuries related to workload spikes and therefore more likely to occur after high workloads compared to other injuries. Finally, Dennis et al. (2002) reported that adolescent fast bowlers who bowled more frequently during a cricket season were more likely to sustain injury. This study also did not focus specifically on lumbar bone stress injuries but there were high proportion of lumbar bone stress injuries amongst the group. As discussed earlier, this study also demonstrated that there was also a trend towards increased injury risk for bowlers who bowled too infrequently (less than two days per week). This suggests that there is a bowling workload that may be optimal, with too much or too little bowling being detrimental. This fits in with the bone remodeling theory discussed earlier, where a particular amount of bone stress may act in a protective manner by improving bone strength, whilst too much bone stress leads to bone break down. Based on this information, fast bowling workload throughout a season and in a bowling session need to be monitored, with appropriate recovery sessions implemented to minimise fatigue and allow bone remodeling to occur. The current bowling recommendations for junior fast bowlers by Cricket Australia (Cricket Australia Junior Cricket Policy, 2004) aim to minimise excessive workloads during the adolescent years, but they do not address the issue of monitoring, compliance to the recommendations and loading patterns, that is, how many recovery days between bowling sessions. More 95

97 research is required in these most vulnerable age groups to determine optimal bowling workloads. Ball speed and release height Fast bowlers who deliver the ball from a greater release height, when expressed as a percentage of standing height, have been associated with an increased risk of lumbar bone stress injury (Elliott, 2000; Foster, et al., 1989). Ball release height is related to the amount of knee extension at front-foot impact, so that a higher release height requires less knee flexion (straighter knee). This increase in knee extension, leads to a stiffer knee segment and greater impact forces (Elliott, 2000; Portus, et al., 2004). Portus et al (2004) reported a positive relationship between a more extended front knee at ball release and higher braking (r =.27) and vertical (r =.22) impact forces. They also demonstrated that bowlers with greater knee extension also reached peak forces more quickly, than those with a more flexed knee at ball release. This explains the higher risk of injury with a higher ball release as larger forces need to be absorbed during the delivery stride. Portus et al. (2004) also demonstrated that faster bowling speeds were associated with more extended knee positions at ball release. It is therefore possible that bowlers, who generated faster bowling speeds, do so because they are able to catapult themselves over a stiffer front leg (therefore losing less energy through the collapsing of the front knee). The consequence could be that faster bowlers may be at greater risk of impact related injury, because many would be using the stiffer knee segment that leads to increased impact forces. 96

98 Finally, there was also a correlation reported between the timing of the maximum hip-shoulder angle and ball release speed, with faster bowlers attaining maximum hipshoulder separation angle after front-foot impact (Portus, et al., 2004). As discussed previously, greater hip-shoulder separation angle is associated with the mixed bowling action and has been linked to increased risk of lumbar spine injury. It possible that this altered timing of hip-shoulder separation angle in faster bowlers may alter loading patterns through the lumbar spine and increase injury risk. Foot biomechanics There is some low level evidence that fast bowlers with a lower longitudinal arch of the foot were at an increased risk of lumbar bone stress injury (Foster, et al., 1989). The increased pronation associated with the lower foot arch is thought result in an altered ability to absorb forces (Nigg, 2001) and has been associated with bone injuries in running athletes (Williams, McClay, & Hamill, 2001). More research is required to link foot biomechanics and lumbar bone stress injuries. Upper body strength Young elite fast bowlers with greater upper body strength, measured with an isokinetic dynamometer, were found to have a significantly higher incidence of back injury including lumbar spine stress fractures (Foster, et al., 1989). It is possible that bowlers with greater upper body strength have higher twisting forces at the spine and generate greater vertical forces, which may contribute to lumbar spine injury (Foster, et al., 1989). More research is required to confirm this relationship. 97

99 Hereditary factors A link between family history and the incidence of spondylolysis suggests possible hereditary factors may be related in the development in this injury (Ebraheim, et al., 1997; Leone, et al., 2011; Lonstein, 1999). Added to this, the difference in incidence rates between Caucasians and African-Americans, and the high rates in isolated Eskimos reported earlier in this chapter further strengthens this link. In the athletic population, this has not been explored extensively. Specifically, family history has not been reported in cricket players with lumbar stress injuries, but a higher incidence of symptomatic stress fractures (mainly at the lumbar spine) have been reported in young female athletes with a family history of osteoporosis or brittle bones (Loud, et al., 2007). From the published injury surveillance studies in cricket playing nations, there is no clear indication whether ethnicity is related to risk of bone stress injuries. The West Indian injury surveillance study reported 12% of all injuries were stress fractures, in Australian Cricket 2% of injuries were stress fractures, whilst in the previous chapter Sri Lankan players had a 6% incidence of stress fractures (Mansingh, et al., 2006; Orchard, et al., 2002). More research to look at potential ethnic differences is required as the evidence in cricket is not as yet compelling. Muscle morphology As discussed earlier in this chapter, there are two main mechanisms by which strain can be translated from physical activity to bone; either through ground impact (reaction) forces or muscle contractions. Whilst impact loading during the fast bowling delivery stride has been widely accepted as a plausible mechanism in the development of 98

100 stress in the posterior elements of the lumbar vertebra in fast bowlers (Glazier, 2010), the role of muscle contractions around the lumbar spine have not been considered until recently (Engstrom, et al., 2007). The major aspects of cricket (bowling and batting) are asymmetrical activities so muscle asymmetry is considered likely. It is therefore not surprising that paraspinal muscle asymmetry has been reported in cricket players of all playing positions (Engstrom, et al., 2007; Hides, Stanton, McMahon, Sims, & Richardson, 2008; Ranson, Burnett, O'Sullivan, Batt, & Kerslake, 2008). What is less clear is whether the asymmetries were as a result of muscle atrophy or hypertrophy, and whether they were related to injury. Hides et al. (2008) used ultrasound to measure the CSA of lumbar multifidus in a group of elite cricket players (batsmen, fast bowlers, spin bowlers and wicket-keepers) and reported smaller CSA in players with low back pain when compared to those in the group with no pain. The same group of authors demonstrated that cricket players of all positions have large ipsilateral (to arm dominance) asymmetries in the CSA of lumbar paraspinal (QL, erector spinae and multifidus) muscles using MRI imaging (Hides, Stanton, Freke, McMahon, & Richardson, 2008). Further they reported that fast bowlers with low back pain had greater asymmetry for QL compared to the fast bowlers without low back pain and all other players in the squad. The results of these studies could not determine whether the asymmetries were due to pain related atrophy, hypertrophy due to excessive muscle activity or whether the asymmetries were present prior to pain because the participants already had low back pain at the start of the study. Others also used MRI to measure the CSA of paraspinal muscles of a group of asymptomatic adult (mean age 26 years) fast bowlers (Ranson, Burnett, O'Sullivan, et al., 99

101 2008). They reported dominant (bowling-arm side) asymmetries for erector spinae, multifidus and QL, whilst psoas was larger on the non-dominant side. Quadratus lumborum was the only muscle with asymmetries of greater than 10% highlighting the possible functional role of QL during the delivery stride. Muscle asymmetries (magnitude and frequency ) were not associated with lumbar spine injury in this study (Ranson, Burnett, King, O'Sullivan, et al., 2008) Engstrom et al. (2007) performed a prospective study using MRI to measure the CSA of paraspinal muscles in a group of asymptomatic adolescent (13-17 years) fast bowlers and followed them for four consecutive cricket season. They reported that QL muscle asymmetry was more common in cricket fast bowlers when compared with age matched controls (swimmers), with the asymmetry favoring the dominant side (bowling side) of the trunk. They reported no asymmetrical differences in other paraspinal muscles (psoas and erector spinae) but did not evaluate players from other playing positions. Importantly they reported that bowlers with larger QL asymmetries were more likely to develop L4 stress fractures of the pars interarticularis (Engstom et al., 1996; Engtrom, Walker, Kippers, & Mehnert, 2007). In particular, asymmetries of QL greater than 18% at baseline were strongly associated with the development of L4 stress fracture. They hypothesized that QL may play a stabilising role around the lumbar spine during the delivery stride as the muscle contracts to control the contralateral side flexion. They also proposed that QL asymmetries on the bowling-arm side, may generate a pattern of loading in the lumbar spine that causes high shear forces on the opposite pars interarticularis leading to bone stress injury (Engstom, et al., 1996). This has been an important development in cricket fast bowling related injury as it moves away from the 100

102 impact loading theory that has been considered the main mechanism for high rates of lumbar bone stress. From the research available it evident that paraspinal asymmetries are common in cricket players and particularly fast bowlers. The role of paraspinal muscle asymmetries in the development of fast bowling injuries needs to be explored further Investigations As discussed earlier in this chapter, asymptomatic pars defects are common in the general (Brooks, et al., 2010; Fredrickson, et al., 1984; Ko & Lee, 2011) and certain sporting populations (Millson, et al., 2004; Ranson, et al., 2005). The long recovery times associated with symptomatic lumbar bone stress fractures and reactions in athletes means an accurate and timely diagnosis is essential so the management plan is tailored to the degree of injury. The patient history and clinical examination are important in making the diagnosis but there is very little scientific research to support clinicians correctly categorising the stage of the bone stress injury. Radiological investigations have an important place in making the diagnosis of acute bone stress injury and can help to determine the severity of injury. There is a range of radiological imaging investigations available to confirm the diagnosis at different stages of the bone stress continuum. Table 3.1 demonstrates how each of the commonly available imaging investigations can be used to identify symptomatic stress reactions and stress fractures; as well as asymptomatic, terminal stage, chronic defects. 101

103 Table 3.1 The role of imaging at different stages of the bone stress continuum Imaging Stage of bone stress injury Pars stress reaction Pars stress fracture Chronic pars defect X-ray (Leone, et al., 2011) Unreliable Unreliable Scotty dog appearance (oblique view); particularly larger defects (Figure 3.2) Computed Unreliable likely to Fracture line (partial Well defined defect tomography demonstrate sclerosis or complete) evident with smooth edges; (Leone, et al., 2011) with irregular edges. incomplete ring sign (Figure 3.4) (Figure 3.4) MRI Bone oedema evident Bone oedema & Defect evident in the (Campbell, et al., with no fracture line fracture line absence of bone 2005; Hollenberg, (Figure 3.5) complete or oedema Beattie, Meyers, incomplete Weinberg, & (Figure 3.6) Adams, 2002) Scintigraphy Increased uptake Increased uptake No increase uptake (Leone, et al., 2011; (Figure 3.3) (Figure 3.3) Read, 1994; van der Wall, et al., 2002) 102

104 X-rays X-ray including anterior-posterior, lateral and oblique views is the least expensive and easiest investigation (Brukner, et al., 1999; Saifuddin, White, Tucker, & Taylor, 1998). The appearance of a Scotty dog with collar on oblique views is representative of pars defect (Figure 3.2), however the inherent weakness of x-rays is that is difficult to know whether this represents a chronic or an acute fracture (Brukner, et al., 1999). X-rays are largely considered unreliable in identifying acute pars fractures or stress reactions because they do not show the new periosteal bone that is associated with stress fractures (Jackson, et al., 1981). Congeni, McCulloch and Swanson (1997) reviewed lumbar spine x-rays of 40 athletes that had CT confirmed pars defects and found that only 45% of the pars defects were visible on plain x-ray. Importantly, the defects that were visible on x-ray were chronically healed indicating that x-ray is a poor option in the diagnosis of early stage fractures. Anderson et al. (2000) compared plain x- rays with single photon emission computed tomography (SPECT), which considered very sensitive to active and early stage bone stress injuries, and reported that only 53% of pars defects evident on SPECT scan were visible on plain x-ray further confirming that plain x-rays are an unreliable method of diagnosis in active stress fractures in the lumbar spine. 103

105 Figure 3.2 X-ray (arrow) and Scotty Dog (circle) appearance of lumbar pars interarticularis stress fracture ( Scintigraphy Bone scan (scintigraphy) is a reliable method of detecting pre-spondylolytic stress reactions and established (active) stress fractures, and is commonly used to confirm a lumbar bone stress injury (Congeni, et al., 1997). Scintigraphy is most valuable in identifying whether a pars defect that is evident on x-ray, MRI or CT scan, is an active stress reaction / fracture or an inactive chronic lesion (Anderson, Sarwark, Conway, Logue, & Schafer, 2000; Letts, et al., 1986; Lusins, Elting, Cicoria, & Goldsmith, 1994; Ralston & Weir, 1998; Sys, et al., 2001). Although a planar bone scan may identify a bone injury, SPECT is preferable as it is more precise and sensitive than plain bone scan as it incorporates a three dimensional component (Brukner, et al., 1999; Ralston & Weir, 1998). Anderson et al.(2000) reported that 20% of patients with a normal bone scan had increased uptake on SPECT. SPECT is also more capable of anatomically localising the area of increased uptake, which is very important in the lumbar spine where there is very 104

106 little distance between potential pain provoking structures such as the facet joints, intervertebral endplates and the pars interarticularis (Anderson, et al., 2000; Lusins, et al., 1994). A typical SPECT scan of a lumbar bone stress injury is demonstrated in Figure 3.3. A weakness of SPECT imaging is that it cannot distinguish between stress reaction and overt fractures as no fracture line is visible, therefore staging of the bone stress injury is not possible (Campbell, et al., 2005). Additionally, scintigraphy involves ionizing radiation to the patient, which is of particular concern as patients with lumbar bone stress injuries are often adolescents. Figure 3.3 SPECT scan appearance of lumbar bone stress injury (arrows) Computed tomography Whilst scintigraphy is very good at demonstrating an active bone lesion, it cannot provide accurate detail on the extent (size) and location of a lumbar stress injury (Brukner, et al., 1999; Congeni, et al., 1997; Sairyo, et al., 2009; Sys, et al., 2001). Computed tomography has long been the investigation of choice to distinguish between 105

107 lumbar spine stress reactions (no fracture line) and a stress fractures (obvious fracture line) (Congeni, et al., 1997). Stress reactions have been classically defined in symptomatic individuals with increased uptake on scintigraphy bone scan (or SPECT) and negative CT scan (Congeni, et al., 1997). This early stage diagnosis is important as there is improved chance of bony healing when pars defects are managed at the early stage (Sairyo, et al., 2009). Computed tomography has also been used to evaluate the extent of osseous healing of stress fractures at the pars interarticularis and helps guide management depending on the chronicity of the defect (Morita, et al., 1995; Sys, et al., 2001). Morita et al. (1995) investigated 185 adolescents with radiologically confirmed active spondylolysis and used CT scans to differentiate the healing potential between early, progressive and terminal stages of a pars defect based on CT imaging (Figure 3.4). They demonstrated that early defects were more capable of osseous healing, with 73% attaining bone healing, whereas those classified as progressive had less ability to attain bone healing with 38% achieving bone healing, whilst no cases of healing were reported in the terminal (chronic) defects. Similarly, Sairyo et al. (2009) used CT imaging to demonstrate the healing potential following early diagnosis of lumbar pars stress fracture. They also showed that early stage defects had much greater healing (87% case with bone healing) potential compared to progressive defects (38%). Once again they demonstrated that chronic stage defects had no healing potential (Sairyo, et al., 2009). 106

108 Figure 3.4 Computed tomography scan of chronic non-united (thick circle) and acute (thin circle) pars defect Magnetic resonance imaging The combination on CT and SPECT imaging had long been considered the gold standard for the diagnosis of active lumbar stress fractures (Campbell, et al., 2005). Magnetic resonance imaging has emerged as possibly a better alternative because it can demonstrate the early stages of this injury as bone oedema (figure 3.5) and more established lesions as fracture lines. It has the additional benefit over CT and SPECT of not subjecting the patient to ionizing radiation. Magnetic resonance imaging is capable of demonstrating the majority of pars defects, with one study finding that 78% of pars defects visible on CT also evident on MRI (Campbell & Grainger, 1999). Campbell et al (2005) compared MRI with CT and SPECT in imaging active lumbar bone stress injuries. Magnetic resonance imaging correlated well in visualizing pars defects when compared 107

109 directly with CT (kappa:.829) and SPECT (kappa:.786). When MRI was compared to a combination of SPECT and CT there was still good correlation (kappa:.786) but MRI was least reliable in determining pars defects at the stress reaction stage (positive SPECT and negative CT). This is suggests that the subtle bone oedema required to make the diagnosis in the early stages of the pathology using MRI is either difficult to identify, missed by some radiologists or there is a lag between SPECT bone uptake and MRI bone oedema. Masci et al. (2006) also demonstrated that MRI was as effective as CT in detecting established lumbar bone stress injuries, with 95% of defects visible on MRI but not as effective when SPECT was added to CT. Again, this indicates that early stage stress fractures are potentially missed on MRI imaging (Masci, et al., 2006). While MRI has been found to have good inter-rater reliability (Campbell & Grainger, 1999) when imaging normal pars interarticularis, its value evaluating early stress fractures at the pars interarticularis is still questionable (Campbell & Grainger, 1999; Masci, et al., 2006; Saifuddin & Burnett, 1997). Sairyo et al. (2006) demonstrated 100% correlation of early stage lumbar stress fractures demonstrated on CT imaging with high signal on MR imaging. They also reported that chronic defects, evident on CT, that also had high signal on MR imaging were likely to achieve bone healing, compared to chronic defects that were MRI signal negative (Sairyo, et al., 2006). They did not use scintigraphy in this study so it cannot be determined how well MRI performed in identifying stress reactions. Although the value of MRI in assessing very early stage pars stress injury is unclear, there is immense potential of the future utilization of MRI to confirm lumbar stress fractures with the benefit of no radiation exposure to the patient. 108

110 The potential for using MRI to predict of lumbar bone stress injury has been recently demonstrated in cricket fast bowlers (Ranson, et al., 2010; Ranson, Burnett, King, O'Sullivan, et al., 2008). Ranson et al. (2008) reported a high correlation between pre-season bone oedema in asymptomatic cricket fast bowlers and symptoms during the next cricket season. The same group of researchers were also involved in a longer term project that included pre-season MRI scans on elite adult fast bowlers for two consecutive cricket seasons. They reported that 53% of bowlers had bone oedema on at least one of the pre-season MRI scans, with 73% of this group going on to develop symptomatic lumbar stress fractures during the next 10 weeks. These studies demonstrate the potential for MRI to be used to prevent lumbar stress fractures but further research is required. Finally, MRI also has been used in to demonstrate the healing after lumbar stress fractures (Sakai, et al., 2010). Sakai et al. (2010) performed monthly MRI scans in a group of adolescent males with confirmed lumbar stress fractures. They reported that 86% of participants had resolved MRI bony oedema after three months, 95% resolved by four months and 100% by five months. The resolution of the bone oedema on the MR imaging correlated well with resolution of low back pain and bone healing on CT imaging. It is likely that with improvements in MRI technology and imaging techniques by radiologist, MRI will become the investigation of choice in making the diagnosis of lumbar bone stress injury. In particular, with improvements in MRI coil strengths that are capable of clearer images, the use of MRI to detect subtle bone oedema is likely. The majority of MRI machines in commercial use are 1.5Tesla, with a recent increase in 109

111 3.0Tesla machines being used. Machines with coil strengths as high as 7.0Tesla are also starting to emerge and could end up being better capable of detecting the bone oedema required to make the pre-symptomatic diagnosis of bone stress (Theysohn et al., 2008). Figure 3.5 Axial T2 fat suppressed MR image of the L3 pars interarticularis bone oedema (circle) consistent with bone stress injury Figure 3.6 Axial T2 fat suppressed MR image of the L5 demonstrating an active stress fracture in the region of the pars interarticularis (fracture line and bone oedema (green arrows)). 110

112 3.12 Management A thorough review of the management of lumbar bone stress injuries is beyond the scope of this thesis but it is important to describe some of the basic principles as they highlight the severity of the injury and the potential impact on an athlete s sporting career. Surgery has been described in the management of recalcitrant pars defects and lumbar bone stress injuries (Deguchi, Rapoff, & Zdeblick, 1999; Hardcastle, 1993; Tokuhashi & Matsuzaki, 1996), but conservative management has been shown to be very successful in resolving low back associated with this injury and returning patients to preinjury function including return to sport (Congeni, et al., 1997; d'hemecourt, et al., 2002; Dubousset, 1997; O'Sullivan, Twomey, & Allison, 1997; Rossi, 1988; Sairyo, et al., 2009; Sys, et al., 2001; Wimberly & Lauerman, 2002). Whilst conservative management results in excellent clinical outcomes, it involves lengthy recovery periods that can keep athletes out of competition for many months (Orchard, et al., 2006; Sairyo, et al., 2006; Sys, et al., 2001; Trainor & Wiesel, 2002). Lumbar pars stress fracture healing times and the resolution of symptoms can take three to six months (Congeni, et al., 1997; d'hemecourt, et al., 2002; Sys, et al., 2001). These time frames fit in well with recent radiological evidence for the resolution of bone oedema (describe above) of three to five months (Sakai, et al., 2010). The lengthy recovery period makes lumbar bone stress injuries the most severe injury (most games-days missed and high prevalence) compared to other cricket injuries as demonstrated by previous cricket injury surveillance studies (Newman, 2003; Orchard, et al., 2006; Stretch, 2003) and in the previous chapter. 111

113 Once the diagnosis of lumbar bone stress injury is confirmed, the management involves ceasing the activities that may have caused the excessive bone stress or may disrupt the healing process. Specifically with cricket fast bowlers, this involves not bowling and most other training activities that involve axial loading, until symptoms have resolved and there is confidence that healing has occurred, either clinically or radiologically. During the recovery period there are many management strategies that have been advocated to improve healing and reduce recurrence, including the use of thoracolumbar bracing (Blanda, et al., 1993; Micheli, 1985; Micheli, et al., 1980; Sakai, et al., 2010; Sys, et al., 2001), technique modification (Burke, Farhart, Moore, Portus, & Sinclair; A. Burnett, Elliott, et al., 1995; Elliott, 2000; Portus, 2003), exercise therapy (Blanda, et al., 1993; Congeni, et al., 1997; d'hemecourt, et al., 2002; Ralston & Weir, 1998; Sys, et al., 2001), lumbar stabilization (Hides, Stanton, Freke, Wilson, et al., 2008; Hides, Stanton, McMahon, et al., 2008; O'Sullivan, et al., 1997) and workload analysis (Dennis, et al., 2003; Orchard, James, Portus, et al., 2009). The use of thoracolumbar bracing to restrict trunk movement, particularly extension, results in increased likelihood of bone healing (Blanda, et al., 1993; Micheli, 1985; Micheli, et al., 1980; Sakai, et al., 2010; Sys, et al., 2001). Despite this, the return to pre-injury level of function is also excellent when brace immobilization was replaced with education and activity modification (Blanda, et al., 1993; Congeni, et al., 1997; Jackson, et al., 1981). The use of brace immobilisation in cricket fast bowlers following lumbar bone stress injury has not been reported in the published literature. Like many overuse injuries, technique analysis and modification have also been advocated for cricket fast bowlers who develop lumbar bone stress injury (Elliott, et al., 112

114 1992; Foster, et al., 1989; Portus, 2001; Ranson, Burnett, King, Patel, et al., 2008). There is however no research that demonstrates lasting changes in bowlers who undergo technique modification and whether it can prevent future injury. The role of exercise therapy in the rehabilitation period is largely untested, however, the paraspinal asymmetries previously reported in cricket fast bowlers and the association with lumbar pars stress fractures, has created interest in the role exercise therapy and rehabilitation in the management of these injuries (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008). Similarly, asymmetry of deep abdominal muscles has also been associated with cricket players with a history of low back pain and has highlighted their possible role in the rehabilitation period (Hides, Stanton, Freke, Wilson, et al., 2008). Finally, the management of bowling workloads has also been advocated, because, as discussed earlier in the chapter, excessive bowling workloads and bowling spikes have been associated with bowlers who develop lumbar bone stress injuries (Dennis, et al., 2004; Foster, et al., 1989; Orchard, James, Portus, et al., 2009). However, there are no prospective studies looking at the impact of workload modification on fast bowling injury, particularly what match or training workloads need modification to alter risk of injury Conclusion Lumbar bone stress injuries are a common and debilitating injury for cricket fast bowlers. The presence of pars defects does not always mean that there will be associated 113

115 pain, but when symptomatic, radiological investigations are require to confirm the diagnosis. Like any bone stress injury, lumbar bone stress injuries, are likely to be associated with excessive repetitive stress through a vulnerable area of bone. The most likely mechanism for this is through impact loading during the delivery stride with certain bowling techniques, with recent links between paraspinal asymmetry and lumbar spine stress fractures creating debate about the role of muscle contraction as a possible mechanism for the development of this injury. With many possible risk factors associated with the development of this injury in fast bowlers the best management approach is still unknown. 114

116 CHAPTER 4: MEASURING QUADRATUS LUMBORUM CROSS SECTIONAL AREA USING MAGNETIC RESONANCE IMAGING: REVIEW AND JUSTIFICATION OF METHODS As discussed in previous chapter, cricket fast bowling is an unnatural activity because it involves a combination trunk lateral flexion, extension and rotation in a short period of time through the delivery stride (Phillips, et al., 2008; Portus, et al., 2004). Appendix D highlights the differences in fast bowling kinematics with the different bowling techniques (Ferdinands, et al., 2009; Foster, et al., 1989; Portus, et al., 2004). Whilst there are published research outlined in the previous chapter that investigate the kinematics and kinetics associated with fast bowling, none of these studies include electromyography of trunk / pelvis muscles during the delivery stride, so muscle activation patterns are unknown. As it is an asymmetrical activity, it is likely that an asymmetrical pattern of muscle activation around the trunk and spine is required to maintain balance and control, and generate power required to deliver the ball. The asymmetrical nature of fast bowling is highlighted by the asymmetrical paraspinal muscle development that has been reported in cricket fast bowlers and highlighted in the previous chapter (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008). To date, asymmetrical muscle development has been reported in cricket players in all positions for multifidus (Hides, Stanton, McMahon, et al., 2008), erector spinae (Hides, Stanton, Freke, Wilson, et al., 2008) and QL (Hides, Stanton, Freke, Wilson, et al., 2008). As reported in Chapter 3, only side-toside differences in muscle size (asymmetry) in the QL have been linked with fast bowling injuries (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008). 115

117 Muscle size, represented by the physiological cross-sectional area (PCSA) of muscle is related to muscle force (Gatton, Pearcy, & Pettet, 1999; Marras, Jorgensen, Granata, & Wiand, 2001; Phillips, et al., 2008). The PCSA is a measure of the muscle volume (attained by placing the muscle portion in a volumetric cylinder) divided by its length (Gatton, et al., 1999; Phillips, et al., 2008). One of the limitations of using PCSA is that it requires the assumption that muscle is a perfectly cylindrical shape, which in reality is not the case. Additionally, the PCSA measure has limited functional value as it is a measurement made in cadavers, which typically involves elderly specimens and not a reflection of the populations that are involved in the athletic activity that result in injury (Marras, et al., 2001). A more functional measurement is muscle CSA that can be measured around the spine using imaging techniques such ultrasound (Hides, Richardson, & Jull, 1996), CT (Danneels, Vanderstraeten, Cambier, Witvrouw, & De Cuyper, 2000) and MRI (Engstrom, et al., 2007; Ranson, Burnett, O'Sullivan, et al., 2008). Using CSA measures to estimate muscle force assumes it is equivalent to PCSA, which it is not, because scan angles, the tapering of muscles near the muscle tendon junctions and the limitations of the imaging methods need to be considered (Gatton, et al., 1999). Nevertheless, CSA is an accepted surrogate measure for PCSA and can be used to demonstrate side-to-side differences in muscle area and therefore asymmetrical muscle activation patterns (McGill, Santaguida, & Stevens, 1993). To date, studies investigating muscle morphology around the trunk and spine have measured the CSA in adolescent (Engstrom, et al., 2007) and adult (Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008) cricket players. Cause and effect is not known, it is possible that the hypertrophy of certain paraspinal muscles, particularly QL, may provide 116

118 the overload required to develop bone stress injury or it may be a sign that abnormal spinal loading led to muscle hypertrophy. If muscle asymmetries are to be considered as a component of the injury prevention and management process, it is important to determine the best methods and techniques for making these measurements. Magnetic resonance imaging, CT and ultrasound imaging can be used to measure the CSA of trunk muscles, and specifically the QL muscle, but all techniques have strengths and weaknesses that need consideration. Ultrasound imaging is less expensive than CT and MRI but provides enough image clarity to reliably measure the CSA of paraspinal muscles (Hides, Richardson, & Jull, 1995). However, it is best suited to measuring smaller superficial structures because it has a limited field of view and inability to image larger muscles in their entirety (Hides, et al., 1995). As such, it has been used to measure the CSA of small paraspinal muscles like lumbar multifidus (Hides, et al., 1995; Hides, Stanton, McMahon, et al., 2008; Hides, Stanton, Mendis, & Sexton, 2011; Sitilertpisan, Hides, Stanton, Paungmali, & Pirunsan, 2012). Ultrasound does not have the same clarity to distinguish muscle boundaries in deeper muscles as CT and MRI; and does not allow the same precision in making lean muscle to fat discrimination as MRI, which are important considerations for measuring CSA (Ranson, Burnett, Kerslake, Batt, & O'Sullivan, 2006). Computed tomography is capable of producing the clear images required to make CSA measurements in trunk muscles (Danneels, et al., 2000). It has been used to compare the CSA of trunk muscles, including QL, in asymptomatic and low back pain populations (Cooper, St Clair Forbes, & Jayson, 1992; Danneels et al., 2001; Danneels, et al., 2000; Hultman, Nordin, Saraste, & Ohlsen, 1993). The major limitation of using CT imaging is 117

119 the exposure of ionizing radiation for participants and is therefore not suitable in the research settings, especially in asymptomatic and younger populations, when other imaging methods are available that do not have the same radiation exposure. Magnetic resonance has been the most widely used imaging technique to measure muscle CSA because it does not involve ionizing radiation and can provide better image clarity to distinguish between muscle, bone and fat when compared to CT and ultrasound imaging (Engstrom, et al., 2007; Flicker et al., 1993; Gibbs, Cross, Cameron, & Houang, 2004; Hides et al., 2007; Hides et al., 2010; Hides, Stanton, Freke, Wilson, et al., 2008; McGill, et al., 1993; Parkkola, Rytokoski, & Kormano, 1993; Ranson, et al., 2006; Tracy, Gibson, Szypryt, Rutherford, & Corlett, 1989). Magnetic resonance imaging has been used to measure QL muscle CSA in the general population (Belavy, Armbrecht, Richardson, Felsenberg, & Hides, 2011; Gibbons, Latikka, Videman, Manninen, & Battie, 1997; Hides, et al., 2007; Kaser et al., 2001; Mannion et al., 2000; Marras, et al., 2001; McGill, et al., 1993; Niemelainen, Briand, & Battie, 2011; Ploumis et al., 2011; Ropponen, Videman, & Battie, 2008; Tracy, et al., 1989) and a number of athletic groups (Guzik, Keller, Szpalski, Park, & Spengler, 1996; Hides, et al., 2010; Iwai et al., 2008; Kubo, Ohta, Takahashi, Kukidome, & Funato, 2007; Raty et al., 1999), including cricket players (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008). The main limitation of using MRI, compared to CT and ultrasound, is that it is more expensive and takes more time to perform. Despite this, MRI is the most popular imaging technique to measure muscle CSA, as evidenced by the number of published studies using this technique to determine muscle size and asymmetry. 118

120 The measurement of CSA using MR imaging allows for side-to-side differences in muscle size to be made and therefore asymmetry calculated; but it is critical to quantify asymmetry with valid and reliable MR techniques that consider the anatomy of the target muscle and its relationship with surrounding structures. As each muscle is bordered by a unique set of structures, which can limit the measurement of CSA from MR imaging, measurement protocols need to be individualized to each muscle to improve reliability and validity of measurements. The aims of this chapter are to; (a) describe the functional anatomy of QL (b) evaluate the methods used in previous research for measuring muscle CSA using MRI, with particular emphasis on the QL muscle (c) describe the role of QL during cricket fast bowling (d) describe limitations of imaging in measuring QL CSA and (e) develop a reliable protocol to measure QL CSA using MRI. 4.1 Methods A thorough review of the literature (up to September 2012) was performed using common databases including Medline, Cumulative Index to Nursing Allied Health (Cinahl), PubMed, Web of Science, ProQuest, Sports Discuss and the Cochrane Library, for studies that used imaging techniques to measure the CSA of QL. The reference list of key research articles was also searched. The research articles that were reviewed for this chapter are outlined in Tables 4.1 and 4.2. Additionally, key papers that described the anatomy and biomechanics of QL were also reviewed. A systematic review was not conducted because it was anticipated that a small number of scientific papers would be found and because of the specificity of the topic it is reasonable to be confident that all 119

121 appropriate papers were sourced. Therefore the results are presented as a synthesis of all papers reviewed. 4.2 Results The functional anatomy quadratus lumborum It is important to consider the anatomy and biomechanical function of QL to ensure that a measurement protocol will provide an accurate assessment of muscle size from imaging. Knowledge of QL anatomy is important when measuring the CSA from imaging scans because CSA measurement is made by carefully outlining muscle, excluding fat and fibrous fascia external to muscle fascia and differentiating the target muscle from surrounding paraspinal muscles (Ploumis, et al., 2011). Understanding the key components of a muscle s morphology should allow for accurate measurement of CSA. Quadratus lumborum is a muscle made of network of fascicles that vary in size and number between individuals (Phillips, et al., 2008). The fascicles attach primarily from the lower anterior surface of the twelfth rib, a 5-7cm portion of the iliac crest and the transverse processes of the L1-4 vertebral levels (Phillips, et al., 2008). There are some minor attachments with the lateral surface of the body of the twelfth vertebra and the iliolumbar ligament (Knuston & Owens, 2005; Phillips, et al., 2008). It has a medial and lateral component, with the medial fibres connecting the lumbar transverse process to the twelfth rib and ilium, whilst the lateral fibres connect the ilium to the twelfth rib (McGill, Juker, & Kropf, 1996). The fascicles are named after their anatomical 120

122 attachments; iliocostal, iliothoracic, iliolumbar and lumbocostal fascicles (Figure 4.1). The fascicles are arranged in three layers (Figure 4.2); the anterior, posterior and middle layers (Phillips, et al., 2008). Compared to other paraspinal muscles (erector spinae and multifidus), the fascicles of QL are up to ten times smaller and therefore thought to be less capable of producing forces to act as primary stabilisers and movers the lumbar spine (Phillips, et al., 2008). Figure 4.1 Model of the fascicles of quadratus lumborum. The small black arrow depicts lumbocostal fascicles. The larger white arrow models the iliolumbar, iliocostal and iliothoracic fascicles. (Phillips, et al., 2008) 121

123 Figure 4.2 Models of the anterior, middle and posterior layers (from left to right) for quadratus lumborum (Phillips, et al., 2008). Based on its lateral position at the spine and the network of fascicles connecting the rib cage, lumbar spine and pelvis; QL is likely to function as a trunk side flexor, extensor and as stabiliser of the lumbar spine and twelfth rib (Knuston & Owens, 2005; Phillips, et al., 2008). Additionally, it is proposed that it acts to raise the pelvic crest through iliac attachments (Knuston & Owens, 2005). Just how much it contributes to these functions is unknown but maybe limited by its relatively small fascicle size and poor mechanical pull compared to other paraspinal muscles (Phillips, et al., 2008). With its vast network of fascicles crossing the lumbar spine, the QL is well positioned to be a spine stabilizer. Due to its lateral location, it is likely that the most significant function for QL is to act as a spinal stabiliser in standing and when trunk lateral flexion occurs. An electromyographic study demonstrated that QL was most active during an isometric side hold position (side plank) and was more active than other paraspinal muscles when compression forces were added to the standing position (McGill, et al., 1996). However, it is only capable of producing a small proportion of the 122

124 compression forces compared to erector spinae and multifidus (Phillips, et al., 2008). Despite been ideally placed to lateral flex the spine, it is estimated that QL only contributes approximately 10% of the lateral flexion strength because of its relatively small fascicles (Phillips, et al., 2008) and small moment arm for lateral flexion (McGill, et al., 1996). Quadratus lumborum has an even smaller moment arm to perform lumbar extension compared to the moment arm for trunk lateral flexion (McGill, et al., 1996). During resisted trunk extension, MRI activation patterns suggests that QL is active but does not contribute the same force as other paraspinal muscles such as multifidus and erector spinae (Mayer, Graves, Clark, Formikell, & Ploutz-Snyder, 2005). This suggests that QL is an agonist to lumbar extension and not a prime mover (McGill, et al., 1996). Interestingly, QL has been shown to be less active during the lower (40%) and higher (70%) ends of force production during trunk extension, with the greatest activation being at approximately 50% of maximal voluntary contraction, suggesting that it has a specific role in supporting other paraspinal muscles during trunk extension but with a limited capacity to work at higher loads (Mayer, et al., 2005). Quadratus lumborum does not appear to be a strong trunk rotator because its line of pull is parallel to the axis of rotation, with other paraspinal muscles (erector spinae) having a superior mechanical advantage to QL (Phillips, et al., 2008). Quadratus Lumborum and Cricket Fast Bowlers As discussed in the previous chapters there are three previous research studies that have investigated the morphology of QL in cricket players, particularly fast bowlers 123

125 (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008). Engstrom et al (2007) performed yearly MRI scans on a group of adolescent fast bowlers over a four year period and compared them to age match controls (swimmers). They compared the magnitude of QL asymmetry between fast bowlers and the controls, and reported that the controls had very little side-to-side CSA differences (asymmetry), whilst the fast bowlers had large asymmetries, that were predominantly favouring the dominant (bowling-arm) side. That is, the QL on the bowling arm side of the spine was consistently larger than the QL on the non-bowlingarm side of the spine. Engstrom et al. (2007) demonstrated a relationship between larger asymmetries in fast bowlers and greater likelihood of sustain lumbar spine stress fractures, which has highlighted the potential that hypertrophied QL muscles may result from an increased stabilisation role or excessive contraction during the bowling action (Engstrom, et al., 2007). Hides et al. (2008) performed MRI scans in a group of elite level adult cricket players. They divided players into two groups depending on their reported history of low back pain (back pain history or no back pain history) and found larger QL asymmetries in those with a history of low back pain. Similarly, to Engstrom et al., fast bowlers had QL asymmetries favouring the dominant side and were larger when compared to players in other positions (batsmen, spin bowlers and wicket-keepers). Ranson et al. (2008) also investigated the morphology of QL and its association to injury in a group of elite level fast bowlers. They reported large asymmetries in fast bowlers but found no correlation between the asymmetries and fast bowling injuries (Ranson, Burnett, King, O'Sullivan, et al., 2008). 124

126 Whilst more research is required to confirm the link between QL asymmetries and fast bowling injury, there appears to be clear evidence that large asymmetries are common in fast bowlers. It is likely that the high rates of trunk side flexion and extension during the bowling action may result in increased QL activation and preferential hypertrophy on one side of the trunk. Alternatively, QL may have a stabilising role during the fast bowlers delivery stride. A mathematical model investigated the role of QL asymmetry during fast bowling and concluded that QL may have a protective role in reducing stress on the spine during the delivery stride (de Visser, et al., 2007). Evaluation of the methods used to measure QL CSA from MRI The key methodological considerations when measuring QL CSA using MR imaging are; (i) the methods used to measure muscle CSA from MR image (ii) the limitations of MR imaging in making CSA measurements i) Methods used for QL CSA measurement There are methodological issues that need consideration with using MRI to measure muscle CSA. This section will address these issues and specifically examine CSA measurements for QL. Manual versus automated technique The measurement of CSA involves identifying and outlining muscle contours using imaging software to determine image pixels that belong to the target object (Harris et al., 1999). With MRI, this can be done either manually or through an automated process (Harris, et al., 1999). The manual method involves manually identifying and 125

127 tracing the outline of the muscle using specialised software by identifying the relevant pixels belonging to the target muscle. The manual technique, although labour intensive, has been shown to be reliable in measuring QL CSA (Engstrom, et al., 2007; Hides, et al., 2010; Hides, Stanton, Freke, Wilson, et al., 2008; Marras, et al., 2001; Ranson, et al., 2006) and considered to be the gold standard in measuring muscle CSA from MRI (Harris, et al., 1999). The automated method was developed to improve reliability and reduce the time take taken to perform measurements (Engstrom, Fripp, & Jurcak, 2011; Harris, et al., 1999). This method has not been used in any of the research studies that have reported QL asymmetry but has been shown to be equally reliable as the manual method in a comparative study (Engstrom, et al., 2011). Asymmetry measurement protocols Muscle asymmetry derived from MRI is defined as the comparison of the size of the muscle on each side based on CSA and is typically referenced by arm or leg dominance (Engstrom, et al., 2007; Hides, et al., 2010; Hides, et al., 1995; Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008). The calculation of QL asymmetry has been made with one of the following calculations: a) Asymmetry = (right CSA / left CSA) x 100 (Engstrom, et al., 2007) b) Asymmetry = ([larger CSA smaller CSA] / larger CSA) x 100 (Niemelainen, et al., 2011) Whilst the methods used to calculate QL CSA and asymmetry in previous research is fairly uniform, there are some methods that are not consistent. In particular, 126

128 which vertebral levels to measure QL, how many image slices to use in determining muscle CSA and methods to enhance visualization of the muscle boundaries have varied considerably (Belavy, et al., 2011; Engstrom, et al., 2007; Gibbons, et al., 1997; Hides, et al., 2010; Hides, Stanton, Freke, Wilson, et al., 2008; Kaser, et al., 2001; Kubo, et al., 2007; Mannion, et al., 2000; Marras, et al., 2001; McGill, et al., 1993; Niemelainen, et al., 2011; Ploumis, et al., 2011; Tracy, et al., 1989). A comparison of methods previously used to measure QL CSA with MRI is outlined in Table 4.1. Studies that reported measurement of the CSA of muscles other than QL were not included as there is no way of knowing if measurement methods are similar in different muscle groups because of different structures bordering them, different tendinous attachments and different angles to the imaging plane compared to QL; all of which can affect measurement accuracy. In this chapter, only one study was included in the analysis when it was obvious that the results reported in two or more studies were from the same authors and used the same set of imaging scans and measurement protocols. Studies identified that have used MRI to measure QL CSA have included athletic cohorts (Engstrom, et al., 2007; Guzik, et al., 1996; Hides, et al., 2010; Hides, Stanton, Freke, Wilson, et al., 2008; Iwai, et al., 2008; Kubo, et al., 2007; Ranson, Burnett, O'Sullivan, et al., 2008; Raty, et al., 1999), general asymptomatic populations (Gibbons, et al., 1997; Marras, et al., 2001; McGill, et al., 1993), populations with low back pain (Mannion, et al., 2000; Ploumis, et al., 2011; Tracy, et al., 1989) and participants subjected to prolonged bed rest (Belavy, et al., 2011; Hides, et al., 2007) (Table 4.1). The methods used to measure QL CSA between these studies vary considerably, which has the potential to influence results (Table 4.1 and Table 4.2). 127

129 There are some basic imaging issues including magnetic field strength of the machine, image slice thickness and the image sequence that need to be considered when using MRI to measure the CSA of muscles. These factors vary between studies but some of the imaging characteristics such as sequence protocol are dependent and specific to the brand of MR machine and limited to the manufacturer s specifications and the radiologists preferences, so will not be considered in this chapter. An important determinant of image quality is the strength of the magnetic field produced by the MR machines, measured in Tesla (T) units (Merkle & Dale, 2006). Whilst coil strengths of up to 7T are now available (Theysohn, et al., 2008), the most commonly used MRI coil strength in the studies outlined in Table 4.1 was the 1.5T, which represents the majority of machines commercially available in the past decade (Theysohn, et al., 2008). Only one study used the more advanced 3.0T machine that is now becoming more widely available (Lescher et al., 2011). The difference in image clarity and measurement reliability between 1.5T and 3.0T machines for measuring QL is unknown. Two studies used considerably weaker coil strengths of 0.15T (Tracy, et al., 1989) and 0.3T (Iwai, et al., 2008), which could limit the image quality and the ability to accurately determine the muscle s fascial borders, but again it is unknown how this would affect the final results. 128

130 Table 4.1 Key characteristics of studies involving QL CSA and asymmetry Study Cohort characteristics Number. (Age, SD or range in years) Injury status McGill et al. (1993) General population. N =15 (25, SD 4) Asymptomatic Tracy et at. (1993) General population. N=26 (29, 17-57) Asymptomatic & LBP Guzik et al. (1996) Recreational athletes. N=16 (25, SD 4) Asymptomatic Gibbons et al. (1997) General population. N=55 (48, 35-67) Asymptomatic Raty et al. (1999) Former elite athletes. N=85 (59, SD 5.3) Asymptomatic & LBP Mannion et al. (2000) General population. N=59 (44 SD 11) Asymptomatic Marras et al. (2001) General population. N=30 (25-30, SD 5-7) Asymptomatic Hides et al. (2007) General population. N=10 9 (33, SD 7) Asymptomatic Kubo et al. (2007) Junior Elite Wrestlers. N=84 (25, SD 4; 23 SD 3; 18 SD 1) Asymptomatic Engstrom et al. (2007) Elite cricket fast bowlers & swimmers N=76 (13-17). Asymptomatic Hides et al. (2008) Elite cricket players. N=26 (21, SD 2) Asymptomatic Iwai et al. (2008) Elite wrestlers / judo. N=28 (20, SD 1) Asymptomatic Ranson et al. (2008) Elite cricket fast bowlers N=46 (26, SD 4) Asymptomatic Ropponen et al. (2008) General population. N=169 (49 SD 8) Asymptomatic & LBP Hides et al. (2010) Elite AFL players. N=54 (22, SD 3.9) Asymptomatic Belavy et al. (2011) General population. N=9 (33, SD 8) Asymptomatic Lescher et al. (2011) General population. N=11 (50, SD 46-53) LBP Ploumis et al. (2011) Military personnel. N=40 (34 SD 8) LBP 129

131 Table 4.2 Methods used to measure QL CSA in previous studies Study Levels (no. QL CSA = all levels sum / Reliability Image enhancement & special features images) mean or single level (ICC) McGill et al. (1993) T12-L4 (5) Single level NR Individual level CSA reported. Images perpendicular to muscle. Tracy et at. (1993) L2-5 (NR) NR NR QL CSA for right side only. Guzik et al. (1996) L1-S1 (4-7) NR NR No Gibbons et al. (1997) L3-4 (NR) NR 0.94 No Raty et al. (1999) L3-4 (1) Single level No Mannion et al. (2000) L3-5 (2) Mean of all levels on one side NR Chronic LBP. Males & females. Marras et al. (2001) L1-4 (11) NR NR Muscle angle adjusted for ACSA. Mean CSA of 3 images / level Hides et al. (2007) L4 (1) Single level Bed rest study. Five measurements over 56 days. Kubo et al. (2007) Jacoby line Single level 90-95% CSA for all back muscles pooled Engstrom et al. (2007) L1-5 (21) Sum all levels 0.98 Measured yearly over 4 years. Used MPT Hides et al. (2008) L3-4 (1) Single level NR Iwai et al. (2008) L3-4 (NR) NR NR CSA normalised to body weight. Ranson et al. (2008) L1-4 (NR) NR 0.96 Measured FCSA. Each vertebral level measured independently Ropponen et al. (2008) L3-4 (NR) NR 0.95 CSF used to determined muscle/fat pixels. CSA for right side muscle. Hides et al. (2010) L3-4 disc (1) Single level NR Measure three times over 18 months. Belavy et al. (2011) L1-5 (15) Mean of all levels on one side NR Bed rest study. Five measurements over 56 days. Lescher et al. (2011) L3-S1 (NR) Mean of all levels on one side 0.93* Reported volume by multiplying CSA with slice thickness Ploumis et al. (2011) L1-S1 (NR) NR 0.92 Axial images corrected for lordosis. Single image at each level NR = not reported, AFL= Australian Football League, CSA= cross-sectional area, FSCA = functional cross-sectional area, MPT = muscle profile templates LBP = low back pain. ICC = intra-class correlation. * Pearson Correlation used. 130

132 The image slice thickness and interslice gap, also varied considerably between studies that measured QL CSA and was largely determined how much of the muscle and how many spinal levels were included in the study. Thinner slices means longer scanning times and were typically used to measure limited sections of the muscle, whilst thick slices and interslice gaps were used when measuring large segments like the entire lumbar region. The main impact that image slice thickness could have on CSA measurement is that thinner slices could result in more images of the target object for analysis but was unlikely to improve image quality and clarity for CSA measurement. The number of images and spinal levels where QL was scanned for CSA measurement has also varied between the studies and may limit comparison of the results (Table 4.2). In most studies only a limited portion of the muscle was measured, which may influence results and comparisons between studies. Ideally, the CSA of a muscle should be measured over the entire length, because the dimensions of muscles such as QL vary in size along their length (Tracy, et al., 1989). For example the upper lumbar spine the QL CSA is approximately 50% smaller than at its largest at the L3-4 level (Marras, et al., 2001). Additionally, the proximity to other structures, particularly muscles that have similar pixel characteristics, varies along its length, which could make it harder to clearly define its borders for CSA measurement at different portions of the muscle (Tracy, et al., 1989). For instance, clear identification of QL in the upper lumbar spine is difficult as it is closely related to the psoas muscle (Tracy, et al., 1989). Attempts to measure QL CSA between the L1 and S1 vertebral levels have been previously reported (Table 4.2), although measurement below its insertion at the iliac crest (L4-5 spinal level) is not possible (Chakraverty, Pynsent, & Isaacs, 2007). Not all studies reported the spinal levels where QL was measured but in those that did, QL was not visible below the L4 spinal level (Ranson, 131

133 Burnett, O'Sullivan, et al., 2008; Tracy, et al., 1989). The majority of studies used scans from a limited number of spinal levels (Table 4.2), most commonly L3-4 vertebral levels (Gibbons, et al., 1997; Hides, et al., 2007; Hides, et al., 2010; Hides, Stanton, Freke, Wilson, et al., 2008; Iwai, et al., 2008; Kubo, et al., 2007; Mannion, et al., 2000; Raty, et al., 1999; Ropponen, et al., 2008). The L3-4 spinal level is where the QL has largest CSA (Kaser, et al., 2001; Marras, et al., 2001) and is thought to be the easiest region to measure QL CSA (Ropponen, et al., 2008). The size differences along the length of QL (increase in size from the upper to the lower lumbar spine) means that the number of image slices used to measure QL could influence the total sum of CSA. Measurements from larger portions of the muscle may overstate CSA differences compared to measurements from smaller portions of the muscle (Marras, et al., 2001; Tracy, et al., 1989). A larger number of images may limit the impact of any measurement error and possibly improve the statistical power to detect differences in CSA and asymmetry. Although most studies reported the number of images where QL was expected to be in the field of view, only some studies reported the specific number of MR images used to measure the QL CSA (Table 4.2). In some cases, a single image was used to measure QL asymmetry, most commonly at the L3-4 spinal level (Hides, et al., 2007; Hides, et al., 2010; Hides, Stanton, Freke, Wilson, et al., 2008; Raty, et al., 1999). Engstrom et al (2007) used image slices from the entire lumbar spine in an attempt to determine the CSA for QL along its entire length but the exact number images included for each participant was not stated. They did however set a minimum sum of CSA for each QL muscle of 2500mm² for inclusion in the final analysis. At its widest, at the L3-4 spinal levels, the QL muscle has a reported CSA of mm² in adult males (Mannion, et al., 2000; Marras, et al., 2001; Tracy, et al., 1989), which would require at least of four images to attain the 2500mm² threshold. In reality the number of images used by Engstrom 132

134 et al. was likely to be greater as they used adolescent participants who were likely to have smaller CSAs than adults and therefore require more QL images to reach the minimum threshold. As they only excluded one participant for not having a summed CSA of 2500mm², it is likely that Engstrom et al. were able to measure more than four images per QL muscle in all but one of their participants. The number of QL images included in a study is not only related to the number of image slices available but also the ability to clearly visualize the muscle borders so that CSA measurements can be made. The measurement of muscle CSA involves carefully outlining muscle mass excluding bone, fat and fibrous fascia not belonging to the muscle (Ploumis, et al., 2011). Methods to enhance the visibility of the QL muscle borders and distinguish them from surrounding structures have been used in some studies. The main purpose for enhancing the image quality is to improve reliability and validity of measurement from the MR images, where superimposition of structures and blurred images are common (Engstrom, et al., 2007; Ranson, Burnett, O'Sullivan, et al., 2008). Engstrom et al. (2007) used muscle profile templates (MPT) to distinguish between muscle borders where partial voluming or fuzzy borders existed. They created templates of the QL muscle at each level and used the templates to determine the muscle borders in each of the subsequent years of the study in instances when the QL borders were not clear. Whilst the reliability reported was very good and the use MPTs is likely to be useful if making repeated measurements on the same participants, it is unlikely to improve measurement validity as it cannot categorically determine the image pixels that belong to a particular muscle. This approach has the potential to cause systematic errors because any error made in the first measurement will be carried over into subsequent measurements. Ranson et al. (2006) used a computerized method of determine the grey scale of imaging pixels that represented the three 133

135 most common tissues in the MRI field of view; muscle, intramuscular fat and bone. They created a grey scale range for each tissue type and used this to distinguish between them during the manual measurement of QL CSA. The main benefit of this method was to improve the accuracy of measuring the lean muscle component of the QL CSA from other structures on MRI and was referred to as the functional cross-sectional area (FCSA). This is expected to be more representative of the muscles contractile ability than CSA measurements that include intramuscular fat (Ranson, et al., 2006). Measurement of fat free tissue also has clinical relevance as fatty tissue has been shown to replace muscle in the presence of pain and intervertebral disc degeneration (Parkkola, et al., 1993). The main problem associated with this method is that there was an overlap in the grey scale ranges between muscles, fat and bone so that absolute certainty of the measurement is not assured. The overlap in grey scale range between bone and the QL is not expected to be an important factor because most of the QL muscle is located away from the vertebral column. It may however create an issue where the muscle attaches to the transverse process throughout the lumbar spine, at the twelfth rib proximally and iliac crest more distally. The ability to dissociate the grey scale between intramuscular fat and muscle may limit the functionality of this method, as there is expected to be an overlap throughout the muscle. The main limitation of this approach is that it cannot be used to distinguish between two adjacent muscles occupying the same area, which is a problem as QL is closely bordered by the psoas muscle in the upper lumbar spine (Tracy, et al., 1989), and by erector spinae and iliacus muscles in the lower lumbar spine (Ploumis, et al., 2011). Ropponen et al. (2008) used the signal intensity of cerebral spinal fluid (CSF) to distinguish between structures that have high water content, such as muscle, and those with low water content, such as fat. This was used to reduce error when measuring muscle from adjoining fat 134

136 and connective tissue. Once again this method does not help distinguish between muscles that are overlapping. The angle between the image plane and the muscle can also create CSA measurement error (Marras, et al., 2001; McGill, et al., 1993). The axial images required to make trunk CSA measurements are typically performed perpendicular to the vertebrae or discs (Marras, et al., 2001; Tracy, et al., 1989). In these views the muscles become oblique to the image plane due to the lumbar lordosis (Tracy, et al., 1989), which can result in an overestimation of the muscle CSA (Delp, Suryanarayanan, Murray, Uhlir, & Triolo, 2001). Some of the studies have overcome this problem by using known QL force vectors to correct for lordosis or have angled the MRI to be perpendicular to the muscle for CSA measurement (Marras, et al., 2001; McGill, et al., 1993; Ploumis, et al., 2011; Ropponen, et al., 2008). Whilst this problem is relevant when using the absolute CSA measurements to the predict muscle forces and function (Marras, et al., 2001; McGill, et al., 1993; Ploumis, et al., 2011), it is less important when determining asymmetry because both sides are equally affected by the overestimation of the CSA. Despite the large number of studies that measured QL CSA with MRI (Table 4.2), only a small number reported bilateral measurements that are required to determine asymmetry (Engstrom, et al., 2007; Guzik, et al., 1996; Hides, et al., 2010; Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008). The majority of studies measured QL bilaterally but did not report the side-to-side measurements, instead reporting the sum of the CSA s from both sides (Belavy, et al., 2011; Gibbons, et al., 1997; Hides, et al., 2007; Iwai, et al., 2008; Kubo, et al., 2007; Lescher, et al., 2011; Mannion, et al., 2000; Marras, et al., 2001; McGill, et al., 1993; Raty, et al., 1999), whilst two other studies only measured the right QL CSA (Ropponen, et al., 2008; Tracy, et al., 1989). 135

137 ii) Limitations of MRI in measuring muscle CSA Despite being the best imaging technique for muscle CSA measurement, there are a number of limitations encountered when using the two dimensional MRI images to measure three dimensional structures. The limitations are not specific to QL but need to be considered when measuring CSA. The main limitations are: a. The partial volume effect is the superimposition of multiple structures in the same area of the scan making it difficult to be certain if the target object is being measured exclusively (Engstrom, et al., 2007; Harris, et al., 1999; Ranson, et al., 2006). This is of particular concern when attempting to identify one structure for CSA measurement where clearly defined borders are essential for accurate measurements (McGill, et al., 1993). To overcome this problem when tracing the target muscle, the grey scale of each pixel needs to be studied and apportioned to one of the overlapping structures (Harris, et al., 1999). b. Optimal alignment of the participant with the scanner is important to minimise the distortion the structure, which can lead to the overestimation or underestimation of the CSA. This is particularly important when comparing side-to-side differences to determine asymmetry, as slight angulation in the coronal plane will make one side appear bigger than the other. As discussed earlier in this chapter, a secondary alignment issue is related to the angle between the target muscle and the image plane (Delp, et al., 2001; Gatton, et al., 1999). Accurate CSA measurement is dependent on the image plane being perpendicular to the target object but as discussed earlier, less of an issue when determining asymmetry (Delp, et al., 2001). This is a particular problem when measuring structures in the lumbar spine as the spine transitions from a kyphosis in the thoracic spine to a lordosis in the lumbar spine and again kyphotic into the sacrum. Paraspinal 136

138 muscles, such as QL that span the length of the lumbar spine, are likely to have differences in CSA measurements with different angles to the scanner from the upper and lower lumbar spine. As muscle CSA is measured in the transverse plane (axial images), an overestimation of the CSA is likely when the angle between the imaging plane and muscle is not perpendicular (Gatton, et al., 1999; Marras, et al., 2001; McGill, et al., 1993). Attempts to attain a more true CSA measurement with MRI, involves the use of vectors of known muscle fibre angles, so that CSA is adjusted to reflect a measurement that is perpendicular to the scanner (Marras, et al., 2001; McGill, et al., 1993). This adjusted measurement is known as the anatomical cross-sectional area (ACSA) and is thought to be a better reflection of the PCSA and therefore the muscles contractile ability (Marras, et al., 2001). c. Movement artifact results from movement of the body part (or with breathing) during the MR imaging sequence. Whilst imaging techniques are used to limit movement artifact (Hides, et al., 1995), the length of time required to complete a full sequence of MR imaging can result in patient movement and therefore distortion of the image. This leads to fuzzy images and difficulty in outlining borders and differentiating between structures. d. The recumbent position used with MRI imaging may result in flattening of the muscle therefore not a truly representing the muscle s geometry in functional positions such as upright standing and bending (McGill, et al., 1993). Whilst this may be a problem when trying to determine function and biomechanical features of the muscle from CSA, it less of problematic when using CSA measurements to determine asymmetry because it is simply a comparison between two sides. 137

139 Development of a quadratus lumborum CSA measurement protocol Previous studies that have measured QL CSA from MRI images have all reported good reliability despite using different methods. However, there is no gold standard in the measurement of paraspinal CSA using MRI imaging (Ranson, Burnett, O'Sullivan, et al., 2008). Based on the methods used in previous studies and taking into consideration the limitations discussed in this chapter, a QL measurement protocol was developed with the aim of making reliable measurements that will allow comparison between studies. The main features and justification of the measurement protocol is outlined below: i. The CSA of QL was measured on the axial scans. As discussed earlier in the chapter, this is the only feasible way of measuring muscle CSA from imaging. ii. A minimum of one set of bilateral QL MRI images was required for participant inclusion in the study. Four of the previous studies (Table 4.2) measured only one image slice to determine QL CSA (Hides, et al., 2007; Hides, et al., 2010; Hides, Stanton, Freke, Wilson, et al., 2008; Raty, et al., 1999). There is no evidence to suggest that multiple image slices is more representative of the muscle CSA than a single image slice. iii. The images were analysed by a single investigator who was blind to all participants details to avoid measurement bias when CSA measures are made. iv. The precise vertebral level of each MRI image that included QL in the field of view (FOV) was identified. As discussed earlier in this chapter, the QL muscle changes in size throughout its length (Tracy, et al., 1989). Identifying the level of each image slice will allow for better comparison with other studies. 138

140 v. The exact location of each image relative to the disc or vertebral body was determined. In particular, each image was assigned a position as representing one of the following spinal locations on the vertebral segment: proximal endplate, distal endplate, mid disc, proximal 1/3 of vertebral body, mid-vertebral body or distal 1/3 of vertebral body. A vertebral level (segment) was defined as, the proximal vertebral endplate of one vertebra to the proximal end plate of the vertebra below it. See Figure 4.3 for clarification of this definition. vi. Quadratus lumborum asymmetry was calculated as a percentage asymmetry at each measureable level, the mean of these measurements was used as the QL asymmetry. Using the mean asymmetry at all levels measured better represents the magnitude of asymmetry at each level and will reduce skewing of results compared to using the sums on each side of the spine. Measuring levels where the muscle is smaller in size will understate the impact on overall asymmetry if compared with levels where the muscle is larger. vii. The manual measurement of QL CSA was completed using an established imaging analysis software program (example Image J 1.36B, National Institutes of Health, USA). As discussed earlier in the chapter, the manual method is an accepted way to measure muscle CSA from imaging. There is no evidence that automated systems improve reliability or validity of measurement. viii. The contour of QL was manually outlined (traced) on each axial image slice using the magnification and freehand functions of the imaging software. As discussed earlier in the chapter, this is an accepted process in making CSA measurements. The level of magnification should is at the discretion of the investigator to allow them to 139

141 accurately visualize the muscle borders. It is unknown whether magnification at one level of will produce better clarity of the target object at all levels. ix. The CSA was calculated on each side of the spine and at each vertebral level where the muscle could be clearly measured. As discussed earlier this chapter, this is the accepted method of determining asymmetry. x. The percentage asymmetry at each level (pair of images with QL in FOV) was calculated using the following equation [(Dominant side CSA / Non-dominant side CSA) x 100]. This is similar to the method described by Engstrom et al. (2007). xi. A minimum standard needs to be set for visualizing the QL muscle borders. See Table 4.3 for imaging quality. Minimum quality rating of 1/3 recommended. L3 L4 L5 Figure 4.3 Defining vertebral segments on MRI between upper vertebral endplates of the vertebra above and below (red lines) 140

142 Image quality scale The measurement protocol above was developed to improve reliability of QL CSA measurements. However, having good reliability does not guarantee that the measurements are valid, that is, the CSA measured truly represents the size of the muscle. The only way to determine validity is to compare cadaver specimens with MR imaging (Mitsiopoulos et al., 1998). This method has been used to demonstrate that MRI is a valid method of measuring CSA in some regions of the lower limb. This unfortunately cannot be extrapolated to the measurement of other muscles, including QL, because each muscle has unique regional anatomy and measurement could be affected by the proximity of adjacent muscles, which could make it difficult to differentiate the fascial borders that separate muscle groups. As described above, QL has its close proximity to psoas, iliacus and erector spinae that can result in measurement error and invalidate results. Based on the knowledge gained of QL anatomy, the techniques used in previous studies and the limitations identified in the previous sections, the measurement protocol should include methods that minimise the risk of invalid measurements. An image quality scale (Table 4.3) was therefore developed to minimise the negative effect of any blurring of muscle borders or superimposition of structures around QL by quantifying the clarity of the target muscle. It is possible that measuring only high quality images may reduce measurement error and increase the validity of the measurements. As part of the image quality scale; images were rated on a four point scale based on the clarity of the muscle boundaries and clarity of the QL muscle (Table 4.3 and Figures 4.4 to 4.7). 141

143 Table 4.3 MRI image quality scale for measuring QL CSA Image Quality Definition (0-3 points) 0/3 points Image quality is poor or QL not clearly visible. No possibility for CSA measurement (Figure 4.4) 1/3 points QL is visible but at least one edge of the muscle is not clear due to superimposing of structures (Figure 4.5) 2/3 points Image quality is good and all edges of QL are clearly delineated from other structures but some blurring of the edges exists (Figure 4.6) 3/3 points Image quality is very good and QL is clearly delineated from other structures with minimal or no blurring of the edge. (Figure 4.7) The highest quality images in the scale (3/3 points in Table 4.3) rely on clear muscle contours and fascial borders, as well as being free of muscle superimposition or distortion due to movement artifact. It is proposed that highest quality images should be analysed independently of the remaining data set and compared to results from images of all image quality (1-3/3). Ideally all images would be of the highest quality so that the investigator can be confident of accurate CSA measurements. 142

144 Psoas QL QL ES Figure 4.4 Example of low quality image (0/3 points) for QL from the quality imaging scale in Table 4.3. Note the superimposing of QL borders with psoas and erector spinae (ES). QL QL Figure 4.5 Example of low quality image (1/3 points) from the quality imaging scale in Table 4.3. Note that QL muscle borders are not clearly visible and there is superimposing of QL borders with surrounding muscles. There is also some movement artifact, particularly on the right side of the image (wave lines within blue circle). 143

145 QL ES Figure 4.6 Example of high quality image (2/3 points) for QL on the right (arrow) from the quality imaging scale in Table 4.3. Note the one blurred border between QL and erector spinae (ES) group. QL QL Figure 4.7 Example of the highest quality image (3/3 points) for QL from the quality imaging scale in Table 4.3. Note that all borders are clearly visible and easy to differentiate from other structures. 144

146 Categorising asymmetry It is important to categorise the magnitude of asymmetry to allow for comparisons between studies and to establish normative values. There is no universally accepted definition of what constitutes asymmetry. Ideally, the definition of asymmetry should be one that has clinical relevance. Ranson et al. (2008) defined asymmetry as a side-to-side difference of greater than 10%, whilst Engstrom et al. (2007) reported that swimmers, used as controls because they were involved in symmetrical movement patterns, had asymmetries of 3%. Additionally, Engstrom et al. reported that asymmetry greater than 18% resulted in increased risk of lumbar spine injury. Hides et al. (2008) also reported that fast bowlers with a history of low back pain had asymmetries of 25% compared to 3% asymmetries in fast bowlers with no low back pain. Therefore, this method proposed that the magnitude of asymmetry is divided into three categories; 0-10%, 11-20% and greater than 20% asymmetry. A side-to-side CSA difference 0-10% can be considered to be small asymmetry, which fits in with the definition used by Ranson et al. and is consistent with the control group in Engstrom et al., as well being consistent with the magnitudes reported in asymptomatic fast bowlers by Hides et al. (2008). The 11-20% category can be considered to be moderate asymmetries and includes the 18% threshold for increased injury risk described by Engstrom et al. The final group (greater than 20%) can be considered to be large asymmetries and is representative of players at greatest risk according to the results of Engstrom et al. and Hides et al. 145

147 4.3 Conclusion The functional role of QL is based on its anatomy, architecture and morphology. Its role in stabilising and moving the spine is somewhat contentious but there is clear evidence that there is preferential hypertrophy of QL during the act of fast bowling in cricket. The review of previous studies that have measured QL CSA using imaging techniques has highlighted some important limitations that need to be considered when reviewing the results from any future studies. In particular, there are substantial issues associated with making valid measurements. Based on the previous studies reviewed in this chapter, a protocol was developed to measure QL CSA. It is proposed that this protocol be used in future studies to allow for uniform measurements of QL CSA. 146

148 CHAPTER 5: QUADRATUS LUMBORUM ASYMMETRY AND LUMBAR SPINE INJURY IN ELITE ADOLECENT CRICKET FAST BOWLERS As discussed in previous chapters, cricket fast bowlers develop lumbar bone stress injuries at similar rates to other high risk sports such as gymnastics (Caine & Nassar, 2005; Kruse & Lemmen, 2009). As demonstrated in Chapters 2 and 3, it is an injury that is largely responsible for the high injury prevalence reported in cricket. Even more concerning is the high incidence of lumbar bone stress injuries amongst adolescent fast bowlers (A. Burnett, Elliott, Foster, & Hardcastle, 1991; Elliott, et al., 1992; Engstrom, et al., 2007; Stretch, 1995), which is similar to other sports that combine young athletes and repetitive spinal loading (Campbell, et al., 2005; Ciullo & Jackson, 1985; Congeni, et al., 1997; Dubousset, 1997; Fujii, et al., 2004; Jackson, et al., 1981; Lonstein, 1999; Morita, et al., 1995; Ruiz-Cotorro, et al., 2006). The mechanisms and processes involved in the development of lumbar bone stress injury, for both adult and adolescent fast bowlers, were discussed extensively in Chapter 3. As discussed in that chapter, one of the most recent risk factors to be identified in adolescent fast bowlers was the presence of QL hypertrophy (Engstrom, et al., 2007). Particularly, Engstrom et al. demonstrated that the 22% of adolescent fast bowlers developed lumbar stress fractures over a four year period, compared to the zero incidence in the age matched controls (swimmers). They reported that a side-to-side QL CSA difference (asymmetry) of greater than 18% favouring the bowlingarm side (dominant-side asymmetry) was present in 73% of bowlers who developed symptomatic lumbar stress fractures and in only 13% of uninjured bowlers. The mean QL asymmetry for all adolescent fast bowlers was 10%. Larger mean QL asymmetries (24%) were reported in bowlers who sustained lumbar bone stress injury compared to uninjured bowlers (7%) and the control group (3%). The predicted risk of lumbar bone stress injury increased with 147

149 larger asymmetries so that bowlers with 5% QL asymmetry were predicted to have a 4% chance of developing lumbar bone stress injury compared to 58% for asymmetries greater than 25% and 78% for asymmetries greater than 30%. They considered the presence of asymmetry to be preferential hypertrophy of QL on the dominant side and proposed that the hypertrophy could result in shear forces across the spine predisposing fast bowlers to lumbar spine injury. To date, no other study has investigated the relationship between of QL asymmetry and lumbar bone stress injury in adolescent fast bowlers, although Hides et al. (2008) and Ranson et al. (2008) investigated this relationship in adult fast bowlers. Hides et al. reported larger QL asymmetries in adult fast bowlers with a previous history of low back pain but no prospective data were reported, whilst Ranson et al. reported no association between asymmetry and lumbar spine injury. In Chapter 4, the methods of using MRI to measure QL CSA were reviewed and the need for uniform methods was discussed. A measurement method protocol was developed from a review of previous research and was used in this chapter. The aims of this chapter were to determine if adolescent cricket fast bowlers have; (a) an asymmetrical pattern of QL development (b) QL asymmetries that favour the muscle on the bowling-arm side (c) an association between larger QL asymmetry and lumbar spine injury. Further to the these aims, this chapter tested the reliability of the measurement protocol developed in Chapter 4 and compared results when using high quality MRI images and images of all quality (1-3/3, Table 4.3) based on the image quality criteria developed in the previous chapter. 148

150 5.1 Methods The MRI scans of 48 adolescent male fast bowlers (mean age of 14.8 years, range years) were accessed from a larger project commissioned by Cricket Australia to investigate a number of different factors associated with injury in fast bowlers, including the relationship between injury and; bowling workload (Dennis, Finch, & Farhart, 2005), bowling technique (unpublished data) and musculoskeletal screening (unpublished data); as well as the correlation between anthropometry and strength characteristics with bowling speed (Pyne, Duthie, Saunders, Petersen, & Portus, 2006). The baseline MRI scans were performed prior to the beginning of an Australian cricket season at a single radiology clinic, using the same MRI machine and protocol. The MRI protocol implemented was identical to that used by Engstrom et al. (2007) to investigate QL asymmetries in junior cricket fast bowlers. The protocol involved T1-weighted 7 mm axial slices with 7 mm gap (TR/TE 500/9.4, 19 image slices, 512 x 512 matrix, FOV 30 x 30) from T12 to L5 vertebral levels using a GE Sigma 1.5T MRI machine (General Electric Medical Systems, Milwaukee, WI). All bowlers reported being injury free at the time of baseline MRI scans and were either preparing to commence or had just started the new cricket season. All MRI scans were reviewed by a single radiologist who was blind to all aspects of the project and reported at baseline as either having radiological evidence of soft tissue pathology (disc, muscle, ligament), lumbar bone stress (bone oedema around the posterior element of the vertebra) or no pathology. The MRI scans of each participant were reviewed by author of this thesis who was blind to participants details including injury status and arm dominance. To determine QL CSA and asymmetry for each participant, the methods described in Chapter 4 were implemented. Specifically, every axial MRI image was individually assessed to determine if QL was in the 149

151 field of view and given an image quality rating based on the criteria developed in Table 4.3. To be included in the study each participant required a minimum of one measurable (grade 1-3/3 in image quality criteria, Table 4.3) set of bilateral QL image slices. The CSA measurements of the QL muscle were made by outlining the contour of the muscle using the magnification and polygon function of an imaging analysis software (Image J 1.36B National Institutes of Health, USA). The CSA was calculated on each side of the spine and at each vertebral level where the muscle could be clearly measured. Quadratus lumborum was imaged between L2 and L5 vertebral levels but QL could only be measured in images slices between the L2 and L4 vertebral levels. There were no images of sufficient quality above the L2 mid-vertebra level and below the L4/L5 disc. All image slices where QL was measureable were then divided into two groups to compare measurement results between high quality (3/3 points) in Method 1 and all (quality) image slices (1-3/3 points) in Method 2. The characteristics of the participants using both methods are outlined in Table 5.1. There were 10 participants who were excluded from final analysis because they did not have MRI images that met the inclusion criteria using Method 1, and four who were excluded using criteria in Method 2. The asymmetry for each participant was determined by using the protocol discussed in Chapter 4, by dividing the CSA of QL image slices on one side by the CSA on the other side of the trunk. The magnitude of asymmetry was divided into three categories (as described in Chapter 4); 0-10%, 11-20% and greater than 20% asymmetry. 150

152 Table 5.1 Adolescent fast bowler characteristics and key findings using two measurement methods No. (mean No. No. paired No. (mean No. of image Vertebral age) at excluded image age) in final slices (Mean levels where baseline slices (%) analysis (range)) QL was imaged Method 48 ( (25%) 38 ( (1-3) L3 L4/5 1 years) years) disc Method 48 ( (53%) 44 ( (1-8) L2 L4/5 2 years) years) disc Note. No. = Number All participants were prospectively monitored throughout the next cricket season as part of the larger project and were required to report any injuries to an experienced sports physiotherapist involved in a separate part of the project. The sports physiotherapist who was involved in another part of the larger study (yet to be published musculoskeletal screening component) was responsible for collecting and disseminating injury information reported by the participants. At the discretion of the sports physiotherapist collecting the injury data, any player who reported low back pain of insidious onset during the cricket season was referred to an experienced sports medicine physician to establish the injury diagnosis using a clinical examination and appropriate radiological investigations. The sports medicine physicians and sports physiotherapists collecting the injury data were not involved in the data analysis for the 151

153 current study and had no knowledge of QL asymmetry status or baseline MR imaging injury status. When further investigation was warranted, additional radiological investigations were performed. Only lumbar spine injuries were included in the final analysis. An injury was defined as a condition that affected availability for team selection, limited performance during a match, or required surgery, based on the cricket injury definition used in injury surveillance projects in Australia at the time of the study (Orchard, et al., 2002) and is similar to the subsequent international consensus of cricket injury (Orchard, et al., 2005). Injuries were divided into the three categories outlined below; lumbar bone stress injuries were confirmed using appropriate radiological imaging techniques including scintigraphy, MRI and CT that are considered to be the gold standard for making the diagnosis (Anderson, et al., 2000; Campbell, et al., 2005; Gregory, et al., 2005; Lusins, et al., 1994; Read, 1994). The injury categories used were; 1. Lumbar bone stress injury (lumbar stress fracture or stress reaction of the posterior vertebral element), 2. Soft tissue lumbar spine injury (any other injury other than bone stress) 3. No lumbar spine injury Participants characteristics including age, mass and height were accessed from the anthropometry data at baseline testing (Pyne, et al., 2006). Using the mass and height details, the body mass index (BMI) was calculated. Written informed consent was received as part of the larger project and ethics approval for this project was obtained from Deakin University Human Research Ethics Committee. 152

154 Data analysis All data (QL CSA, injury and general characteristics) were entered into a spreadsheet (Microsoft Excel 2003). For each participant, the CSAs were summed to give the total area of the QL on each side of the vertebral column. At each imaging level of the vertebral column, the absolute difference between the dominant and non-dominant side QL CSA was measured and used to calculate the percentage difference in CSA between sides. The absolute values (mm 2 ) and percentage difference between sides were summed to give an overall value for absolute difference and percentage difference between dominant and non-dominant side muscles. An example of the calculation of the asymmetry for each participant is demonstrated in Table 5.2 using hypothetical data. Table 5.2 Example of calculation method for QL asymmetry Participant 1 Participant 2 QL Images Left CSA (mm²) Right CSA (mm²) % difference Left CSA (mm²) Right CSA (mm²) % difference Image Image Image Image Image Mean asymmetry

155 The Mann-Whitney test was used to compare the magnitude of QL asymmetry between dominant and non-dominant sides of the trunk. The Fisher s exact test was used to determine statistical significance between categorical measures of dominant and non-dominant QL asymmetries. Chi Square test was used to examine the distribution of participants in the three injury groups and the three asymmetry categories. The Kruskal-Wallis test was used to compare mean QL asymmetry in participants across the three injury categories (stress fracture, soft tissue injury and no injury). Participants were placed into two groups, a stress fracture group and a nonstress fracture group, so a comparison can be made with results of previous research that used similar injury category groups. The Mann-Whitney test was used to compare QL asymmetry in participants with lumbar stress fractures and those who did not sustain a stress fracture. Nonparametric tests were chosen as a conservative option because of the differences in group sample size. Because of this we did not formally test for normality as the tests are not dependent on a normal distribution. Significance was set at p < Intraclass correlations were used to examine reliability. A reliability of >.90 was considered to be reasonable (Portney & Watkins, 2000). 5.2 Results Asymmetry The results reported were in this section involve Method 1, using high quality images only, unless stated otherwise. The intra-class correlation coefficient for repeated measurements of QL asymmetry for randomly selected images (18%) was excellent (ICC=.966, 95% CI ). 154

156 The mean QL asymmetry of the participants was 13.1% (range %). An asymmetry of 0-10% was the most frequent finding (Table 5.3). Twenty-one (55%) participants had QL asymmetries greater than 10%. Table 5.3 Magnitude of QL asymmetry in adolescent fast bowlers Asymmetry Number of bowlers (n (%)) 0-10% 17 (44%) 11-20% 13 (34%) >20% 8 (21%) The QL asymmetries were sub-divided as either larger muscle CSA on the dominant (bowling-arm) or non-dominant side of the body. There was a similar distribution of asymmetry between dominant (55%) and non-dominant (45%) sides. Asymmetry on the non-dominant side was significantly larger (16.4%) when compared to the dominant side QL (10.5%) (Z = -2.07, p = 0.038). Additionally, there was also a significant difference between dominant and nondominant QL asymmetries when the data were analysed using the three magnitude categories (p = 0.037, Table 5.4). 155

157 Table 5.4 Asymmetry categories and dominance for adolescent fast bowlers (p = 0.037) QL asymmetry Side of larger muscle size 0-10% 11-20% >20% Dominant asymmetry Non-dominant asymmetry Using measurement Method 2, which included a larger number of images for analysis (Table 5.1), similar results were obtained. Comparison between Method 1 and Method 2 is represented in Table 5.5. The mean CSA for each image slice using Method 2 was 581mm² (SD 146.3mm²) and the mean total summed CSA for QL in each participant was 2216 mm² (SD 966.3mm²). The mean QL asymmetry was 12.8% per participant and there was no significant difference between the CSA of QL dominant (14.7%) and non-dominant (11.2%) sides. Additionally there was a similar distribution between dominant (48%) and non-dominant (52%) side asymmetries. Fifty-two percent of participants had asymmetries greater than 10%. The majority (48%) of participants had asymmetries magnitudes of 0-10%, compared to those with 11-20% asymmetry (34%) and those with greater than 20% asymmetry (18%). 156

158 Table 5.5 Comparison between measurement Method 1 and Method 2 for determining QL CSA Key measurements Method 1 (n=38) Method 2 (n=44) Statistical analysis Mean QL CSA for one image level 611 (146) 581 (146) (mm², (SD)) Mean QL CSA for each participant 977 (515) 2216 (966) (mm², (SD)) Mean QL asymmetry (%) t-test p=.87 Mean dominant side asymmetry (%) t-test p=.19 Mean non-dominant side asymmetry (%) t-test p=.74 Distribution of dominant side asymmetries (%) OR=1.48 (CI ) p=.38 χ²=.79 Distribution of asymmetries > 20% (%) OR=1.2 (CI ) p=.74 χ²=.11 Injury Eight bowlers (21%) developed symptomatic lumbar spine stress fractures and stress reactions of the pars interarticularis (bone stress injury) during the cricket season. Four were bilateral; three on the non-bowling side and one on the bowling (dominant) side of the spine. Of 157

159 the bone stress injuries, two were at the L4 vertebral level and five at the L5 level, whilst one participant had both L4 and L5 levels affected. There was no difference between bowlers who sustained lumbar bone stress injuries and those with no lumbar bone stress injury (soft tissue injury and no injury groups), in terms of age (Mann-Whitney Z=-.950, p=.342) and height (Mann-Whitney Z=-.609, p=.543) (Table 5.6). Participants mass was also not different between groups (Mann-Whitney Z=-1.755, p=.079), although there was a trend towards significance, with those injured (lumbar bone stress) having the greater body weight. In fact, the lumbar bone stress injury group was approximately eight months older, four centimetres taller and nine kilograms heavier than the group that did not sustain bone stress injury. These differences were reflected in the BMI, as bowlers who sustained a bone stress injury during the cricket season had a significantly higher BMI than those who sustained a soft tissue injury or no injury (p=.02, Table 5.6). There were four (asymptomatic) participants with radiological evidence of lumbar bone stress at baseline (pre-season) MRI scanning and all four went on to develop symptomatic bone stress injury during the cricket season. Of the remaining four participants who developed lumbar bone stress injury, one had a lumbar soft tissue injury at baseline and the remaining three had no radiological evidence of injury at baseline. Nine participants developed pain categorised as soft tissue lumbar spine injuries during the cricket season. Eight of these players had radiological evidence of soft tissue injury on baseline MR images, whilst one other player who developed a soft-tissue lumbar injury had no radiological evidence of injury on baseline MRI (Table 5.7). Of the 26 players who had no 158

160 radiological evidence of injury at baseline, four developed either a soft tissue lumbar injury (n=1) or bone stress injury (n=3). Table 5.6 General characteristics for adolescent fast bowlers (Mann-Whitney Z = 2.39, p=.016) Key characteristics Mean age (years) Range, SD Lumbar bone stress injury group (n=8) 15.5 ( , 1.51) No bone stress injury group (n=30) 14.8 ( , 1.29 ) Mean height (cm) Range, SD Mean mass (kg) Range, SD 179 ( , 5.23) 73 (62-82, 7.67) 175 ( , 10.59) 64 (35-92,13.23) Body Mass Index Range, SD 22.6 ( , 1.73) 20.7 ( , 1.72) 159

161 Table 5.7 Radiological status of adolescent fast bowlers at baseline and during the season Injury Status Baseline - Radiological status (%) During season - Radiological status (%) Lumbar Soft Tissue Injury 8 (21) 9 (24) Lumbar Bone Stress 4 (11) 8 (21) No Injury 26 (68) 21ª (55) Note. ªonly participants who had appropriate clinical symptoms had radiological investigations during the season. Therefore the 21 participants, who had no injury during the season in this table, did not have any radiological investigations. Injury and asymmetry The magnitude of QL asymmetry was divided into three groups and compared to injury status (Table 5.8). There was no association between asymmetry and injury status (χ 2 (4) = 6.28, p =.180). When participants were categorised as either having bone stress injury or no bone stress injury; and asymmetry less or more than 20% (Table 5.9), the relative risk (RR) was significant at 3.75 (CI 95% , p =.024). All the participants with asymmetry magnitude greater than 20% had asymmetry favouring the non-dominant side. There was no association between the mean asymmetry for players who sustained lumbar spine injury (soft tissue (12.5%) and bone stress (15.7%)) and those players who were uninjured (12.4%, χ 2 (2) = 1.242, p=.537). When the participants were grouped as either having a lumbar 160

162 bone stress injury (mean QL asymmetry 15.7%) or no bone stress injury (mean QL asymmetry 12.4%), there was still no significant difference in QL asymmetry (Mann-Whitney Z= -1.11, p=.267). A post-hoc power analysis was performed on the data comparing the stress fracture group and the remaining participants (soft tissue injury and no injury groups). The power analysis showed that the study was powered at 15% (β=.85) to detect differences in CSA of QL between the group with stress fractures and those without stress fractures. Table 5.8 Injury status and magnitude of QL asymmetry for adolescent fast bowlers Number players injured (%) Magnitude of Lumbar bone Lumbar soft asymmetry stress injury tissue injury No injury 0<10% 3 (7.9) 5 (13.2) 9 (23) 10-20% 1 (2.6) 3 (7.9) 9 (23.7) >20% 4 ( (2.6) 3 (7.9) 161

163 Table 5.9 Bone stress injury status and QL asymmetry for adolescent fast bowlers Injury status Asymmetry category Bone stress injury No injury >20% asymmetry 4 4 <20% asymmetry Discussion The asymmetrical nature of fast bowling is highlighted in this study as QL asymmetry was a common finding, which is consistent with previous research involving both adolescent and adult fast bowlers (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008). An asymmetry of greater than 10% has been previously used to classify fast bowlers as having asymmetrical paraspinal muscle development (Ranson, Burnett, O'Sullivan, et al., 2008) and consistent the magnitudes of asymmetry reported in adolescent swimmers who are expected to have symmetrical muscle development due to the bilateral nature of their sport (Engstrom, et al., 2007). Additionally, none of the adolescent fast bowlers with QL asymmetries of less than 10% went to develop lumbar stress fractures in the previous study (Engstrom, et al., 2007). In the current study, 55% of participants had asymmetries greater than 10%, which is similar to the 47% of asymmetries reported by Ranson et al. (2008) in adult fast bowlers. The mean asymmetry (13.1%) for the fast bowlers in the current study was similar to that reported by Engstrom et al. (2007) in adolescent fast bowlers (10.5%). The range of asymmetry in the current study (range %) means that some bowlers had asymmetries 162

164 large enough (greater than 18%) to place them at high risk of lumbar spine stress fractures previous identified by Engstrom et al. (2007). Previous studies have reported larger QL asymmetries predominantly on the bowling-arm side in adult (Hides, Stanton, Freke, Wilson, et al., 2008) and adolescent fast bowlers (Engstrom, et al., 2007). In the current study there was similar proportion of QL asymmetries favouring the dominant (55%) and dominant (45%) side, whilst the magnitude of asymmetry was significantly larger on the non-dominant QL muscle. The difference in results between the current study and Hides et al. may be explained by the age and level of participation of the bowlers. In particular, Hides et al. used elite level adult bowlers selected for an off-season high performance training camp at a national cricket academy, highlighting a high level of professionalism and exclusivity to cricket, whilst the participants in the current study were younger and not likely to be exclusively involved in cricket, so that other sporting activities could impact on their muscle development patterns. It is also likely that the bowlers in Hides et al. had greater lifetime bowling workloads, which may have resulted in greater asymmetrical muscle development expected from repetitive asymmetrical loading. The differences in the distribution of dominant and non-dominant side asymmetries between the current study and that of Engstrom et al. (2007) are harder to explain because the participants were a similar age. It is possible that differences in the methods used in the two studies may account for the different results. A main difference was that Engstrom et al. measured QL CSA over four consecutive years compared to the single pre-season measurement in the current study. It is possible that QL may alter morphologically as the bowler matured, particularly as the participants in both studies were likely pubertal (13-17 years) and rapid muscle development is expected. A second difference is that in the current study, MRI images 163

165 were excluded when the QL muscle contours were considerably obstructed or superimposed by surrounding structures, whereas Engstrom et al. (2007) facilitated measurement of poorer quality images by using MPTs (see Chapter 4), developed from measurements made in previous years, and therefore had a larger number of QL images to measure. Whilst Engstrom et al. reported good reliability in measurement using this method, there is no way of knowing whether the measurements were valid. Their approach could result in systematic measurement error because the superimposition of surrounding structures may overstate the size of the muscle. In the current study the iliacus muscle was regularly superimposed over QL in MRI images below the L4 vertebral level and could easily be mistaken as part of QL. Whilst the validity of measurement in the current study could not be tested, the use of the image quality criteria at least excluded the poorest images where superimposition of structures was likely to result in measurement error. This study reported no association between the mean QL muscle asymmetry and lumbar spine injury during the cricket season, which is consistent with previous reports in adult fast bowlers (Ranson, Burnett, King, O'Sullivan, et al., 2008) but contrary to Engstrom et al. (2007), who reported the larger asymmetries in adolescent fast bowlers with lumbar stress fractures. Participants with asymmetries greater than 20% had a greater RR of developing lumbar bone stress injury than those with asymmetries less than 20%. Whilst this finding can be viewed as being consistent with Engstrom et al., who reported asymmetries greater than 18% related to lumbar stress fractures, the participants in the current study with greater than 20% asymmetry all had non-dominant side asymmetries, which is contrary to Engstrom et al. It is also important to note that whilst there were four participants (50%) who fell into this category (greater than 20% asymmetry and lumbar bone stress injury), there were also three participants (38%) who developed lumbar bone stress injuries and had asymmetries less than 10%. Again this is different 164

166 to Engstrom et al. who reported that none of the adolescent bowlers who developed lumbar stress fractures had asymmetries less than 10%. It is likely that that the small number of participants in the study and the low number of participants injured may be responsible for the greater RR, as the post hoc power was low. Engstrom et al. reported that most lumbar bone stress injuries (92%) occurred at the L4 vertebral level. In the current study, only 25% of participants had bone stress injuries exclusively at the L4 level, whilst, the L5 vertebral level was the most commonly affected, which is consistent with previous studies reported in Chapter 2. It is unclear why Engstrom s cohort had such a high proportion of L4 vertebral fractures. Apart from the different methods used, another possible reason for the different results reported by Engstrom et al. (2007) and the current study may be related to bowling technique differences between participants. As discussed in Chapter 2, there are different types of fast bowling techniques that involve different rates of trunk side-flexion, rotation and extension (Portus, et al., 2004; Ranson, Burnett, King, Patel, et al., 2008). It is possible that amount of trunk rotation, side-flexion and extension during the delivery stride may influence the level of QL activation and hypertrophy (de Visser, et al., 2007). Bowling kinematics were not considered in either study, so it is possible that bowling technique differences existed, which may have altered activation patterns of QL and therefore muscle CSA. To date, there is no research that has investigated the relationship between bowling technique kinematics and paraspinal crosssectional area, however de Visser et al. (2007) used a finite element model to demonstrate that QL asymmetry may be related to QL activation during the extreme postures adopted in the latter part of the bowling technique (rotation extension and side flexion). Interestingly, they hypothesised that dominant side asymmetry may be protective of lumbar pars interarticularis stress fractures in fast bowlers. 165

167 In previous chapters, it was highlighted that lumbar bone stress injuries are common in adolescent athletes in many sports such as gymnastics (Caine & Nassar, 2005; Kruse & Lemmen, 2009), tennis (Ruiz-Cotorro, et al., 2006) and soccer (Gregory, et al., 2004) and less prevalent once physical maturity is attained (Nazarian, 1992). All participants in this study were adolescent but age was not significantly different between those who sustained lumbar spine stress injury and those who did not. The participants mass (weight) was one characteristic of the injured participants in this study that demonstrated a trend towards significance. Additionally, BMI was significantly higher in the bone stress group of fast bowlers, when compared to the rest of the cohort. It is possible that greater body mass as proportion of height (BMI) may predispose bowlers to greater impact forces during the delivery stride and possibly increase the risk of lumbar bone stress injury, particularly in the presence of an immature skeletal system. The finding of greater BMI in the bone stress group in the current study is similar to that reported in adolescent female athletes who developed stress fractures (predominantly lumbar stress fractures) (Loud, et al., 2007).The greater body mass and BMI of the injured athletes could also indicate that they are further advanced in puberty compared to the uninjured group. Pubertal status was not measured in this study but could be another factor that may predispose adolescent fast bowlers to lumbar bone stress injury and needs to be considered in future research. It was concerning that 21% of adolescent fast bowlers in this study developed symptomatic lumbar bone stress injury during a single cricket season. This is similar to the rate of injury reported by Engstrom et al. (2007) but their data were collected over four cricket seasons, where a greater incidence of injury over a longer time period would be expected. The rate of lumbar spine injury in the current study is also similar to that reported in elite adult fast bowlers by Ranson et al. (2008). The participants in the current study are in an age group that is 166

168 governed by Cricket Australia s bowling workload restrictions, to help reduce injury rates in skeletally immature bowlers. This high injury rate suggests more needs to be done to prevent lumbar spine injuries in junior fast bowlers. An interesting finding from the current study was that all fast bowlers who had radiological evidence of lumbar bone stress at baseline (pre-season) went on to develop symptomatic stress fractures during the cricket season. Whilst only four of the participants fell into this category, this is may be an indication that MRI imaging could be used as a predictor of future bone stress injury. Ranson et al. (2008) similarly reported that 70% (n=10) of adult fast bowlers with evidence of lumbar bone stress at pre-season MRI imaging, went on to develop symptomatic lumbar bone stress injury over the next cricket season. This finding is also consistent with another recent study where a significant number of asymptomatic adult cricket fast bowlers, who had lumbar pars interarticularis high signal on MRI, went on to develop symptomatic stress fractures in the following 28 weeks (mean 11 weeks) (Ranson, et al., 2010). The genesis of bone stress injuries is unknown, so it is possible that the loading in the time between radiological evidence of bone oedema and the development of clinical symptoms, may be a pivotal part of understanding the process. Further research using larger cohorts of cricket fast bowlers is required to investigate this further. As discussed in the previous chapter, there is no universally accepted method of measuring QL asymmetry. In this study, a rigorous method (Method 1) for measurement was applied to help improve the validity of measurements and was compared against a less strict method (Method 2) that allowed more CSA measurements to be included. The mean asymmetry results using both methods varied slightly but were not significantly different. By using strict criteria for including MRI images in this study (Method 1), 75% of all MRI image slices were 167

169 excluded from analysis and resulted in a smaller total CSA per person (977mm²) compared to the second method (2216mm²). Both methods resulted in smaller total CSA s when compared to Engstrom et al. (2007), who only included bowlers with a CSA of more than 2500mm² in their final analysis. Using this approach, they excluded one bowler from their study, whereas in the current study, even using the less strict criteria the mean asymmetry was still smaller than the minimum used by Engstrom et al. The use of MPTs by Engstrom et al. that projected the templates from previous images to improve measurement at levels where the muscle contours were distorted or fuzzy may have resulted in more images included and larger CSA measures compared to the current study. In the current study, images falling in these categories were excluded because measurement accuracy could not be guaranteed. Fewer image slices and smaller summed cross-sectional areas resulted, which could further explain some of the differences in results. One of the aims of this study was to determine if the use of fewer high quality images was reliable method of measuring QL CSA and compare it to the using a larger number of images of any quality. The excellent reliability with the high quality method and the similarity in asymmetry results with the second method suggest that it is the technique that should be used. The current study demonstrated that QL was most clearly measurable in the L3-4 vertebral region where the QL has largest CSA (Kaser, et al., 2001; Marras, et al., 2001) and is considered to be the easiest region to measure (Ropponen, et al., 2008). There were no MRI images included in Method 1 above the L2 vertebral level where the muscle is at its narrowest (Tracy, et al., 1989) and at L5 vertebral level near its insertion into the iliac crest; mainly because it was so closely related to iliacus. This measurement profile differed from Ranson et al. (2008) who reported QL measurements at the L1 and L2 vertebral levels but like the current study there 168

170 were no measurements possible at the L5 level. Ranson et al. used the grey scale range of MRI signal intensity of lean paraspinal muscle to differentiate muscle from surrounding bone and fat (described in Chapter 4). This may account for their ability to measure at levels that were not possible in the current study. Additionally, the participants in Ranson et al. study were older (mean age 26 years) and skeletally mature, with more defined paraspinal musculature expected, which may have made the QL easier to measure over more vertebral levels. This study confirmed a consistent problem with all research involving the measurement of three dimensional structures such as muscle by using two-dimensional MRI images. The presence of overlapping structures was common, making it difficult to determine the target object boundaries, which resulted in partial volume averaging as the overlapping structures caused erroneous image pixel signal and resulted in a large number of images being excluded from final analysis. Additionally, there were problems associated with motion artifact and errors in alignment of the participant in the MRI machine, which resulted in angulations and therefore distortion of structures and possible measurement errors. Any angulation issues would be of particular concern in this sort of project as it involved comparison of structures from the left and right side of the trunk to assess whether asymmetries existed. The use of the image quality criteria developed in the previous chapter helped to grade the image quality and limited the potential measurement error associated with partial volume effect and angulation. This is the first study to quantify image quality and future researchers should consider this approach. Finally, a limitation for this study is that it was under-powered (15%) due to the small sample size and low number of players with lumbar bone stress injury. This would have increased the likelihood that a relationship between lumbar bone stress injury and asymmetry may have been missed. Despite this, the current study used a similar number of participants and 169

171 had similar number of players with lumbar bone stress injury as other studies (Engstrom, et al., 2007; Ranson, Burnett, O'Sullivan, et al., 2008). Additionally, other paraspinal muscles (psoas, erector spinae and multifidus) were not measured so it is unknown whether asymmetries in these muscles may have been associated with injury. This was considered unlikely when the methods for the study were being developed as previous MRI studies had demonstrated no relationship between the CSA of these muscles and injury in cricket fast bowlers (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008). 5.3 Conclusion This study demonstrated that adolescent cricket fast bowlers have QL asymmetries on both the dominant and non-dominant sides of the body. These results were similar using two different methods for including MR images. Further research is required to compare the different methods used in this study and evaluate the validity of measuring the CSA of QL using MR images. There were a high number of lumbar bone stress injuries in this group of fast bowlers but, unlike previous research involving adolescent fast bowlers, injuries were not related to QL asymmetries. Further research is required to determine if differences found from previous research are related to factors such as bowling technique and anthropometry or perhaps the differences in the study methods. Additionally, research comparing paraspinal asymmetries with fast bowling techniques and workloads are required to fully understand the nature of the asymmetries described in the current and previous research. 170

172 CHAPTER 6: ADULT CRICKET FAST BOWLERS WITHOUT LOW BACK PAIN HAVE LARGER QUADRATUS LUMBORUM ASYMMETRY THAN INJURED BOWLERS Asymmetrical paraspinal muscle development has been previously reported in both adolescent (Engstrom, et al., 2007) and adult cricket fast bowlers (Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, King, O'Sullivan, et al., 2008), and this has created interest in the role of paraspinal muscle asymmetry in fast bowling injury. Whilst there is no disputing that the asymmetrical nature of fast bowling techniques is most likely responsible for this, the adolescent fast bowlers in Chapter 5 had QL asymmetries distributed fairly equally between the dominant and non-dominant sides of the trunk. This is contrary to previous studies that reported QL asymmetries predominantly on the dominant side of the trunk in both adolescent and adult fast bowlers respectively (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008). Importantly, there was no association between QL asymmetries and lumbar spine injury in the previous chapter, which is inconsistent with the results reported by Engstrom et al. in a similarly age group of bowlers. The results in Chapter 5 question whether large QL asymmetry has a role to play in lumbar spine injury in adolescent fast bowlers. In adult fast bowlers the results have been equally inconsistent. Hides et al. reported that fast bowlers with a history of low back pain had larger QL asymmetry than their counter-parts who had no relevant lumbar spine injury history, whilst Ranson et al. (2008) found no relationship between QL asymmetry and lumbar spine injury in the adult fast bowlers. Chapter 5 highlighted a higher RR of lumbar bone stress injury for bowlers with asymmetries greater than 20%. As discussed, these results need to be considered with caution as there was similar number of participants who developed lumbar bone stress injury that had 171

173 asymmetries less than 10%. An interesting link between injury and asymmetry found in the previous chapter was the relationship between larger BMI and lumbar bone stress injury. It is likely that the young age of the participants in the previous chapter was partly responsible for this, especially as they were near puberty when growth spurts occur. If this is the case, the link between BMI and injury would not be present in adult fast bowlers. In Chapter 4, a method for measuring QL muscle asymmetry was described by grading MRI images and comparing bilateral CSA measurements from axial slices. Using only high quality images where QL is clearly visible in the field of view resulted in a high proportion (75%) of all MRI images being excluded due to insufficient quality. The main difference between the high and low quality MRI images was clearer muscle borders and less superimposition of structures around the target muscle. As discussed in the previous chapter, this method does not guarantee validity of the measurement, but it does increase confidence that only QL was measured and not adjacent structures. Using these established methods of measuring QL asymmetry, it was important to compare the pattern of QL asymmetry and its relationship to lumbar spine injury in adult fast bowlers with the results reported in the adolescent fast bowlers in the previous chapter. The aims of the current study were to prospectively determine; 1) the magnitude and side of QL asymmetries in elite adult cricket fast bowlers 2) the relationship between asymmetry and lumbar bone stress injury using reliable methods established previously 3) the association between basic anthropometry and lumbar spine injury in adult fast bowlers. 172

174 6.1 Methods Twenty-three elite adult male fast bowlers, participating at national or international level, with a mean age of 24.0 years (SD 3.6 years, range years) were included in the study. They had a mean height of 187.3cm (range cm, SD 4.9cm), mass 87.3 (range kg, SD 8.3kg) and body mass index (BMI) of 24.9 (range , SD 2.3). Each participant had an MRI scan of the lumbosacral region prior to the start of a cricket season (baseline imaging). The participants were selected in the study because they were part of an elite group of bowlers identified by cricket selection panels as potential international players and were part of a larger study conducted by Cricket Australia s Sports Science and Sports Medicine program. General characteristics (mass, height details and BMI) were collected as part of the larger project (Pyne, et al., 2006). The participants were injury free and had commenced playing grade cricket in preparation for the Australian domestic competition at the time of the baseline MRI imaging. All participants were part of Australian state squads and monitored through the cricket season as part of Cricket Australia s injury surveillance program (Orchard, et al., 2006). Any lumbar spine injury reported during the surveillance period was assessed by a qualified sports medicine physician in the participant s home state, with further investigations, including MRI, CT and scintigraphy scans, ordered to help confirm diagnosis. All injuries and injury data for this study was collected from the national injury surveillance database from the 2002 / 2003 cricket season (Orchard, et al., 2006). The lumbar spine injuries included in this study were distributed into one of the following three categories at the end of the cricket season; 1. Lumbar bone stress injury (lumbar stress fracture or stress reaction of the posterior vertebral element), which was confirmed radiologically (scintigraphy, MR or CT). 173

175 2. Soft tissue lumbar spine injury (any other injury other than bone stress) 3. No lumbar spine injury Baseline MRI imaging to measure QL CSA was performed at a single radiology clinic using the same MRI protocol that has been reported in the previous chapter. A single radiologist assessed all baseline MRI images for pre-existing radiological abnormalities. The baseline images were assigned to one of the three injury categories above, based on the radiologist report. Bone oedema at the posterior element of the vertebra was classified as radiological evidence of lumbar bone stress, whilst any other musculoskeletal abnormality to the vertebral segment was defined as radiological soft tissue pathology. This classification at baseline was made using appearance of the baseline MRI images only and not confirmed with clinical testing as participants were injury free and participating unrestricted in training and match activities. All participants continued to train and play no matter what radiological group they were in unless they reported pain during the cricket season, at which point they were assessed by team medical staff. Written consent was gained from the participants in the study and ethics approval for the project was obtained from Deakin University Human Ethics Committee. Each MRI image was assessed for image clarity using a previously described four-point scale (Chapter 4, Table 4.3), by a single researcher (thesis author) who was blind to all participants details. The method (Method 1) that included high quality images only described in previous chapters was used in the final analysis. The CSA of QL was measured using the methods described previously (Chapter 4), so that the contour of QL was outlined and measured on each axial image slice on each side of the spine and at each vertebral level where the muscle 174

176 could be clearly identified. This method of measurement was shown to be reliable in the previous chapter. As in the previous chapter, each participant required a minimum of one pair of QL image slices of sufficient quality to be included in this study and all participants had a suitable set scans a for analysis. Quadratus lumborum was imaged between the L2 and L5 vertebral levels. Only 35% of all MRI images were of sufficient quality to be included for analysis with a mean of three paired image slices (range 2-5) per participant. All images of sufficient quality that were included for analysis were located between the L2 and L4 vertebral levels. There were no images of sufficient quality above the L2 mid-vertebra level and below the L4/L5 disc level. Based on preseason MRI images there were nine (40%) participants with no abnormality detected, ten (43%) with soft-tissue pathology and four (18%) with bone oedema on the posterior element of the vertebra. Data analysis All data were entered into a spread sheet (Microsoft Excel 2003). The methods used to determine side-to-side differences in CSA (asymmetry) for each participant were described in Chapter 4 and were the same methods used in the adolescent study (Chapter 5). The Kruskal- Wallis test was used to examine differences in age, height, mass and BMI between participants in each of the three injury groups. The Wilcoxon test was used to analyse differences between the dominant and non-dominant side asymmetries. The Kruskal-Wallis, Mann-Whitney U and Fisher Exact tests were used to determine differences between magnitude of asymmetry and injury status. Non-parametric tests were chosen as a conservative option because of the 175

177 differences in group sample size. Because of this we did not formally test for normality as the tests are not dependent on a normal distribution. An alpha level of.05 was set. 6.2 Results Asymmetry The mean CSA of QL for each image slice was 879mm² (SD 190mm²) and the mean total summed CSA per participant was 2635mm² (SD 814mm²). The mean QL asymmetry of all participants was 11.5% (range %). The majority of participants (52%) had asymmetries of 0-10% (Table 6.1). There were a greater proportion of dominant (bowling-arm) side asymmetries (65%) than non-dominant side (35%) asymmetries (Table 6.1). Asymmetry magnitudes that favoured the dominant side were larger (13.3%) than those on the non-dominant (8.2%) side but the difference was not significant (p=.069). The difference in the mean CSA between the dominant and nondominant QL was 52 mm² and the Typical Error of measurement was 22 mm². 176

178 Table 6.1 Distribution of QL asymmetry dominance in adult fast bowlers (Wilcox Test, p=069) Asymmetry category Total (%) Dominance (side) 0-10% 11-20% >20% Dominant (bowling-arm side) Non-dominant (non-bowling-arm side) (65%) (35%) Total 12 (52%) 7 (31%) 4 (17%) Injury Eight participants (34%) developed symptomatic and radiologically confirmed lumbar bone stress injuries during the cricket season. Ten (43%) participants developed soft tissue lumbar spine injuries and the remaining five (22%) reported no lumbar spine injury. Four participants (17%) had radiological evidence of lumbar bone stress at baseline and all went on to develop symptomatic lumbar stress fractures. Of the remaining four players who developed lumbar bone stress injuries, one had radiological evidence of a lumbar soft tissue injury and three no radiological abnormality of injury at baseline MRI imaging. Nine of the ten participants who developed a soft tissue lumbar spine injury during the cricket season had radiological evidence of soft tissue lumbar spine injury at baseline. The one 177

179 remaining participant who developed soft tissue injury had no radiological abnormality at baseline MRI imaging. There were nine participants who had no radiological abnormalities at baseline testing. Of these, three developed lumbar bone stress injury and one developed soft tissue lumbar spine injury. There was no significant difference in participants age (Kruskal-Wallis p=.269), mass (Kruskal-Wallis p=.233), height (Kruskal-Wallis p=.387) and BMI (Kruskal-Wallis p=.153) between the three injury groups (Table 6.2). Table 6.2 Injury and anthropometry for adult fast bowlers No injury Soft Tissue Lumbar Spine Injury Lumbar bone stress injury Mean Age (SD) 22.5 years (2.9) 25.4 years (3.9) 23.1 years (3.5) (p=.269) Mean Mass (SD) 84.1 kg (7.9) 90.6 kg (10.0) 85.3 kg (4.9) (p=.233) Mean Height (SD) cm (5.5) cm (5.4) cm (3.5) (p=.387) Mean BMI (SD) 23.7 (2.1) 25.5 (2.9) 24.9 (1.1) (p=.153) 178

180 Injury and asymmetry Mean asymmetry by injury status was; 20.2% for no injury, 7.6% for soft tissue injury and 11.1% for lumbar bone stress injury. Participants with no injury had larger asymmetries when compared to those in the soft tissue and bone stress groups (Kruskal-Wallis p= 0.050). There was no significant difference between the number of participants in each injury group and asymmetry categories (p=.090, Table 6.3). Table 6.3 Distribution of injury (%) and magnitude of QL asymmetry for adult fast bowlers (Kruskal-Wallis, p=.090) Asymmetry Lumbar soft Lumbar bone category No injury tissue injury stress injury 0<10% 1 (20%) 7 (70%) 4 (50%) 10-20% 1 (20%) 3 (30%) 3 (38%) >20% 3 (60%) 0 (0%) 1 (12%) When the group with no injury was combined with the soft tissue injury group (11.8% asymmetry) and compared to the lumbar bone stress group (11.1% asymmetry), there was no significant difference in mean asymmetry (p=.949). When participants were grouped as either having no injury (20.2% asymmetry) or any (soft tissue and bone stress) lumbar injury (9.1% asymmetry), there was a significant difference between groups (Mann-Whitney U Test p=.025). As with the adolescent group in the previous chapter, the odds ratio was determined by 179

181 categorising participants in asymmetry status and comparing it to the development of lumbar bone stress injury (Table 6.4). Table 6.4 Odds Ratio for QL asymmetry status and lumbar bone stress injury in adult fast bowlers Magnitude QL Asymmetry Lumbar bone stress No lumbar bone stress (%) injury injury Total > < Total When participants with greater than 10% asymmetry were only included for analysis, there was strong trend (Kruskal-Wallis p=. 05) between those with no injury (23% asymmetry) and the other two groups (lumbar bone stress 17% asymmetry and soft tissue 11% asymmetry). A post-hoc power analysis was performed on the data comparing the stress fracture group and the remaining participants (soft tissue injury and no injury groups). The power analysis showed that the study was powered at 85% (β=.15) to detect differences in CSA of QL between the group with no injury and those with lumbar injury. 6.3 Discussion The main aim of this chapter was to determine if large QL asymmetries were linked with increased risk of lumbar spine injury in adult fast bowlers. Similar to the results in adolescent 180

182 fast bowlers in the previous chapter, this was not the case. In fact, the adult fast bowlers in the current study who did not sustain injury during the cricket season had larger QL asymmetries, than bowlers who developed injury. This is contrary to previous research where large QL asymmetries have been associated with lumbar spine injuries in adolescent and adult fast bowlers (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008). However, Ranson et al. reported no relationship between lumbar bone stress injuries and larger QL muscle asymmetry in elite level adult fast bowlers (Ranson, Burnett, King, O'Sullivan, et al., 2008). Not surprisingly, QL asymmetry was a common finding in this group of bowlers; however the majority (52%) had asymmetries of less than 10% magnitude. This is similar to the adolescent fast bowlers in the previous chapter. Only a relatively small proportion (17%) of participants had asymmetries of greater than 20%, and all on the dominant side QL. This is a similar proportion (21%) of larger QL asymmetries (greater than 20%) found in the adolescent fast bowlers in the previous chapter. However in the adolescent group, all the larger asymmetries favoured the non-dominant side which is contrary to the results in this chapter. It is difficult to explain this difference between the two studies but it may be related to the age differences between the two groups of bowlers. In particular, muscle development may be a reflection of the number of deliveries bowled throughout a player s career and the associated repetitive muscle contractions. If this was the case, adult fast bowlers are more likely to have the sufficient historical workload to develop a pattern of muscle development that reflects fast bowling, particularly as the younger bowlers may have been involved in more than one regular sporting activity, which could alter the pattern of muscle development. The adult bowlers in the current study were professional bowlers and unlikely to be involved in any other sport. Bowling technique was not considered in either study and could also explain this difference (see below). 181

183 The possible differences in career bowling workloads and level of professionalism between the adolescent and adult fast bowlers may also explain the difference in the pattern of QL asymmetry seen. In the current study, dominant side asymmetries were present in almost two thirds of participants, which is consistent with previous studies in adolescent and adult fast bowlers (Engstrom, et al., 2007; Ranson, Burnett, O'Sullivan, et al., 2008). A more non-specific pattern of QL asymmetry was in found adolescent fast bowlers in the previous chapter, with 55% of bowlers having asymmetries favouring the dominant side. It is also possible that differences in bowling techniques could explain the differences in asymmetry patterns between studies. As discussed previously, the paraspinal asymmetries that exist in cricket fast bowlers are likely to be an indication of the asymmetrical nature of bowling and is likely to be linked to the amount of trunk rotation, extension and side flexion through the delivery stride (Ferdinands, et al., 2009; Portus, et al., 2004; Portus, et al., 2000). The activation and subsequent hypertrophy of QL may therefore be related to bowling kinematics (de Visser, et al., 2007) with QL activation and hypertrophy likely as it acts as a trunk stabilizer and side flexor (de Visser, et al., 2007; Guzik, et al., 1996; McGill, et al., 1996). As bowling technique was not measured in any of these studies this cannot be confirmed. More research is required to determine whether bowling technique is associated with larger QL size. Whilst QL asymmetry is a common finding in fast bowlers, it is unknown what magnitude of asymmetry is important clinically. As described previously, Engstrom et al. (2007) reported that QL asymmetries greater than 18% were associated to lumbar stress fractures in adolescent cricket fast bowlers. The larger asymmetries (greater than 20%) in the current study were not related to lumbar spine injury. In fact, fast bowlers with no lumbar spine injury had larger asymmetries than those who sustained soft tissue or lumbar bone stress injury. This has 182

184 not been reported previously and it is possible that fast bowlers with less trunk side-flexion in bowling technique and therefore less QL activation, may be more at risk of lumbar spine injury than those with more trunk side flexion. Once again, as bowling kinematics were not included in this study, it is not possible to confirm this theory. Alternatively, it is possible that QL hypertrophy may part of a protective mechanism, possibly as trunk stabiliser. The larger career and seasonal bowling workloads may explain the greater proportion of lumbar bone stress and soft tissue injuries in the adult fast bowlers in the current chapter compared to the adolescent bowlers in the previous chapter and in Engstrom et al. (2007). With almost one third of bowlers (34%) in the current study developing symptomatic lumbar bone stress injury in one cricket season, it highlights the extent of this problem, particularly as it is an injury that requires a long recovery period (Chapter 2 and 3). It is important to consider that the mean age of the bowlers was under 25 years and as discussed in Chapter 3, this age group would still be at high risk for lumbar bone stress injuries as they are unlikely to have reached musculoskeletal maturity. The mean age of participants in this study was similar to the age (25 years of age) of the international level Sri Lankan fast bowlers reported in Chapter 2, but it is unknown if they were representative of other Australian bowlers competing at first class level because they were part of group identified as players with future prospects, which typically has a focus on younger players. The proportion of bowlers who sustained bone stress injuries in the current study is only slightly higher than the 25% reported in British adult elite fast bowlers in one season (Ranson, Burnett, King, O'Sullivan, et al., 2008). During the one cricket season, 83% of bowlers either developed lumbar bone stress injuries or soft tissue injuries, highlighting that fast bowling is high injury risk activity, even in adult bowlers. The adult bowlers in current study sustained almost double the rate of soft tissue 183

185 injuries than the adolescents reported in the previous chapter. This difference may be related to high seasonal and lifetime bowling workloads in the adult bowlers, which may result in degenerative changes in lumbar spine structures such as the intervertebral disc and facet joints. This is supported by the difference in baseline (pre-season) soft-tissue pathology in this study (55%) compared to the adolescents outlined in Table 5.7 of the previous chapter (40%). The bowlers in the current study were professional players competing at elite level and have been reported to bowl in excess of 300 deliveries per week (Orchard, James, Portus, et al., 2009), whilst the adolescent bowlers in the previous chapter were at an age governed by Cricket Australia s bowling workload restrictions for training and matches (Cricket Australia Junior Cricket Policy, 2004), therefore restricted to a maximum of deliveries per week (depending on their age). High impact forces associated with fast bowling can lead to degeneration in load bearing structures around the spine such as the intervertebral disc, which is a possible source of soft tissue injury. As discussed in Chapter 3, previous studies have identified that fast bowlers have high rates of disc degeneration and the degenerative process begins in adolescence (Elliott, et al., 1993; Elliott, et al., 1992; Foster, et al., 1989; Hardcastle, et al., 1992; Ranson, et al., 2010), so it is possible that the extra years of bowling of the participants in the current study may have resulted in increased degenerative injuries in adulthood. Additionally, the expected higher match workloads and intensity associated with professional cricket fast bowlers may help contribute to the higher rate of soft tissue injury. In the previous chapter, it was proposed that the age of the bowlers may have been related to the association identified between BMI (and to a lesser extent body mass) and injury. The adult bowlers in the current chapter had no association between any of the anthropometry 184

186 measures and injury, which strengthens the theory that the expected changes with puberty may be responsible for the relationship in the adolescent group. In the previous chapter four asymptomatic bowlers who had pre-season MRI bone oedema (posterior vertebral element) went on to develop symptomatic bone stress injuries during the next cricket season, similar to findings of previous studies (Ranson, 2010; Ranson, Burnett, King, O'Sullivan, et al., 2008). In the current study, all four participants with baseline MRI bone oedema also went on to develop symptomatic lumbar bone stress injuries. As discussed in the previous chapter, this finding may have important clinical implications if MRI can be used to predict bone stress injuries in the pre-symptomatic stage. The pathogenesis of lumbar bone stress injury may be in the months prior to the presentation of symptoms, which may be reflected in the bone oedema demonstrated in the asymptomatic bowlers. This pattern of MRI bone oedema may be the reverse process to the resolution of bone oedema evident in the three to four months after lumbar spine stress fractures reported previously (Sairyo, et al., 2006). It is therefore possible that MRI imaging could be used as a screening tool in athletes in sports determined to be high risk for bone stress injuries, as early detection of bone stress injuries may result in shorter recovery periods. Further studies are required to monitor athletes over a longer period of time to determine the role of radiological oedema in the development of lumbar bone stress injuries. There are several limitations of this study. Similar to other studies, there were a small number of participants but was still well powered to detect links between lumbar bone stress injuries and QL cross-sectional area. Bowling workload data and bowling technique kinematics were not included in this study and may have affected the characteristics of muscle asymmetries demonstrated. 185

187 6.4 Conclusion Predominantly dominant side QL asymmetry was shown in a high proportion of adult fast bowlers. A high rate of lumbar bone stress injury was also evident this group of cohort of adult fast bowlers. Surprisingly, fast bowlers who did not sustain a lumbar spine injury had larger magnitudes of asymmetry compared to bowlers who were injured. The finding that bone oedema on pre-season MRI resulted in symptomatic lumbar bone stress injury warrants further research. In particular, a longitudinal study with a larger number of participants and more regular MRI scanning could confirm the usefulness of MRI as a screening tool for detecting pre-symptomatic lumbar bone stress. Future research also needs to be directed at determining the role and activation patterns of key muscles around the trunk using EMG or MR imaging in combination with three dimensional kinematic data. 186

188 CHAPTER 7: THESIS DISCUSSION The primary purpose of this thesis was to investigate the nature and severity of injuries associated with fast bowling and the risk factors for these injuries. A recurring theme of early cricket research was that fast bowlers have the highest incidence, prevalence and most severe injuries, compared to other playing positions. This highlighted the different physical demands of fast bowling compared to batting, spin bowling and wicket-keeping, and in particular, the role of the interrelated risk factors of bowling technique and high workloads. One of the major reasons for the high injury prevalence and severity associated with fast bowling was the alarmingly high rates of lumbar spine (pars interarticularis) bone stress injuries that have been traditionally linked to technique and workloads. Despite convincing historical data that fast bowlers were most affected by injury and particularly lumbar bone stress injuries; there were some obvious gaps in the literature. One of the gaps was that previous injury surveillance studies published were limited to a small number of cricket playing nations, with most research coming out of Australia, South African, England and the New Zealand. The missing link was the lack injury surveillance data from teams in the Indian subcontinent that make up 40% of the countries that have International Cricket Council Test playing status, and where playing conditions are different to Australia, South Africa, England and New Zealand. As discussed in Chapter 1, cricket is one of few sports that are influenced by conditions such as climate, soil types, ground sizes and the nature of cricket pitches. In particular, the Indian subcontinent is known for its low bouncing wickets that necessitate more overs bowled by spin bowlers compared to fast bowlers. This was highlighted in Chapter 2, where Sri Lankan fast bowlers, bowled a lower proportion of deliveries in matches played in the Indian subcontinent compared to when games were played in other countries 187

189 including South Africa and England. Aside from the obvious differences in pitches, the climate differences between countries discussed in Chapter 1, may also affect levels of dehydration and fatigue. Apart from the lack of injury surveillance from the Indian subcontinent teams such as Sri Lanka, another gap in the cricket injury research was the lack of consensus on some key risk factors associated with lumbar bone stress injuries. Bowling technique, bowling workloads and age have been consistently associated with lumbar bone stress injuries. The most recent factor, QL muscle asymmetry, had not been rigorously tested, with reports of strong association with lumbar bone stress injuries in adolescent fast bowlers reported in one study (Engstrom, et al., 2007), conflicting with another study that reported no association with injury in adult fast bowlers (Ranson, Burnett, King, O'Sullivan, et al., 2008). Apart from the age differences of the cohorts in these two studies, the methods used to measure QL CSA and therefore determine asymmetry varied. In reviewing the published studies that measured QL asymmetries in other sports and general population in Chapter 4, it was obvious that a lack of consensus in methods existed, which could also explain some of the differences between studies. 7.1 Thesis Aims The purpose of this thesis was to explore these gaps in the literature and was reflected by the thesis aims outlined in Chapter 1. In this chapter the thesis aims will be reviewed and outcomes discussed. 188

190 Aim 1 Examine the epidemiology of cricket injuries in Sri Lankan players Some of the injury characteristics of the Sri Lankan cricket team were similar to that reported in in other cricket playing nations. In particular, the overall match incidence, ODI and Test match incidence were similar in the Sri Lankan cohort compared to all other countries (Australia, England and New Zealand) except for the South African team. There were also a similar proportion of new, compared to recurring, injuries and total number of injuries per year. The high proportion of new injuries is a likely reflection of the elite sports medicine facilities available to international teams, so that injuries are well managed to prevent recurrence. It would be interesting to compare these rates with those of non-professional players to determine the impact of higher standards of medical care and compliance with rehabilitation programs. The similarity in the number of injuries between teams may be related to similar scheduling for international teams. In particular, Test playing nations need to comply with the International Cricket Councils Future Tours Program that requires them to play against each other over a set time cycle. This results in uniformity in the playing schedule for the elite teams and possibly reflects the similar number injuries that are sustained by each team. A difference between the Sri Lankan and both the Australian and South African data was that fielding was the most common injury mechanism in Sri Lankan players, compared to bowling from the other studies. As the majority of games played by the Sri Lankan team during the study period were either at home or in a country within the Indian subcontinent region, it may a subtle reflection lower dependence in fast bowlers compared to the Australian and South African teams. 189

191 Future research should be aimed at collecting injury surveillance data from all Test playing countries using the definitions described in the international consensus paper (Orchard, et al., 2005) over a prolonged period of time. This will allow better comparison between cricket playing countries and regions. Aim 2 Assess whether Sri Lankan fast bowlers had the similar injury characteristics as elite bowlers from other parts of the world. Despite bowling a smaller proportion of overs, during the two year surveillance period, than bowlers from other countries, the Sri Lankan fast bowlers were still three times more likely to be injured compared to other playing positions, had the highest injury incidence, highest injury prevalence and sustained the most severe injuries than any other playing position. This emphasises the different kinetic and kinematics between fast bowling and spin bowling; and that the stress on the musculoskeletal system is greater for fast bowling than other positions. It likely that Sri Lankan fast bowlers bowled less than their counterparts from some other cricket playing nations, which could explain the small proportion (9%) of bowlers who developed lumbar bone stress injuries compared to those reported in the England (Newman, 2003; Ranson, et al., 2010) and the elite Australian bowlers. Even if the Sri Lankan bowlers had bowled less in matches, the combination of match and training bowling workloads placed them at risk of common fast bowling injuries, such as bone stress injuries. As demonstrated previously (Dennis, et al., 2003; Orchard, James, Portus, et al., 2009), injury risk for fast bowlers is related to bowling workloads. The loading threshold required to develop bone stress injuries is unknown and is likely to be different for each bowler with factors such as bowling technique, age, musculoskeletal strength and biomechanics (lower limb / pelvis) 190

192 all part of an algorithm that determines bone strain rates and fractures thresholds. This would mean that some bowlers need less bowling loads to develop lumbar bone stress injuries and explain why a small number of the Sri Lankan bowlers developed this injury during the surveillance study in Chapter 2. It again highlights that fast bowling is an unnatural activity and places high load through vulnerable regions of the musculoskeletal system, such as the lumbar pars interarticularis. In particular, the asymmetrical nature, the extreme range of movement and the high impact forces associated with fast bowling creates a unique pattern of injury that differentiates it from most other sporting activities. Future research needs to be aimed creating a more extensive database of fast bowling injuries, with particular emphasis on the country of origin, age, technique and bowling workloads. This will help develop a profile to suit the individual bowler s unique characteristics and help predict future injury. Additionally, it may be possible to determine the proportion of overs that slower bowlers need to bowl, to have a protective benefit in reducing fast bowling injuries. This can only occur by having a worldwide injury surveillance program that includes a large number of matches played in the Indian subcontinent, where slower bowlers are expected to play a greater role in the longer formats of the game. Aim 3 Develop methods of measuring paraspinal muscle size The asymmetrical nature of fast bowling was most evident in the patterns of muscle hypertrophy reported in the previous literature (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008; Ranson, Burnett, O'Sullivan, et al., 2008) and in Chapters 5 and 6 of this thesis. In particular, QL asymmetries were highlighted, with some studies showing a link to 191

193 injury (Engstrom, et al., 2007; Hides, Stanton, Freke, Wilson, et al., 2008) and others not (Ranson, Burnett, King, O'Sullivan, et al., 2008), including the studies in Chapters 5 and 6. The inconsistencies in the research regarding the role of QL asymmetry in fast bowling injuries may be related to differences in bowling techniques, workloads and possibly age between cohorts studied. It was also likely that the methods used to measure QL CSA and therefore determine asymmetry may be also related to the differences found. In Chapter 4, the vast differences in methods used to determine CSA of QL from MRI scans in both cricket studies and other sporting groups were highlighted. The main difficulty in trying to measure muscle asymmetry from MRI scans is that the two-dimensional images do not allow for distinction between the overlapping of structures. As discussed in Chapter 4, QL is closely related to other paraspinal and hip muscles, resulting in overlapping of structures and making it particularly difficult to measure the CSA. An important aspect of this thesis was to create a method to measure QL CSA, partly based on previous studies and taking into consideration QL s unique anatomy. The goal was to create a method that was reliable and minimised the measurement error related to poor image quality and superimposition of structures. One of the cricket studies that demonstrated a link between QL and injury, used methods to facilitate measurement of poorer quality images by using templates from previous measurements in the same individual (Engstrom, et al., 2007). As discussed in Chapter 5, this has the potential for systematic measurement error and may explain some of the differences in results between that particular study and others (Ranson, Burnett, King, O'Sullivan, et al., 2008), including those reported in Chapter 5 and 6. Ranson et al. (2006) used the pixel greyscale to distinguish between structures (muscle, bone and fat) and was more likely reduce error from the overlapping of structures. In Chapter 4, a clear method was proposed and tested in subsequent 192

194 chapters (Chapter 5 and 6). Specifically, the creation of minimum standards for image quality based on the clarity of muscle boundaries (Table 4.3) resulted in a large proportion of images being excluded from final analysis for QL CSA. It is virtually impossible to totally eliminate the errors associated with overlapping structures when using MRI to measure CSA, however, measuring the QL images with the clearest boundaries, at least increases confidence that the objected measured is QL only. These methods were tested in Chapters 5 and 6, and shown to be reliable. By excluding poorer quality images, it was evident that QL was best measured at the L3 and L4 levels, where it is at its widest and has less association with neighboring structures. It is proposed that future studies measuring QL CSA should focus on the L3 and L4 vertebral levels. It is clear that muscle CSA can be measured on MRI scans, but in future research, consideration is needed when planning such studies to minimise errors by using one of the established methods (Chapter 4 or Ranson et al. (2006)), high Tesla machines and use small gap and slice thickness. Additionally, it is important to understand the local anatomy well when making such measurements because the overlapping of structures can result in measurement error. Aim 4 Describe the paraspinal muscle morphology of adolescent and adult cricket fast bowlers In Chapters 5 and 6 of this thesis, the pattern of QL asymmetry was described in both adolescent and adult cricket players. Both groups had side-to-side differences in QL size (CSA) that varied from small (less than 10%) to quite large (greater than 20%). Why these differences exist between players is unknown but likely to be related to bowling technique and workloads, especially as QL has the potential to act as a trunk stabiliser and side flexor. As discussed 193

195 throughout the thesis, there are considerable variations in the bowling techniques between players that result in differences in the amount of trunk side flexion, extension and rotation. As technique and workload was not considered in these studies it is hard to determine how it was related to asymmetry measurements. An interesting finding was that the pattern of asymmetry varied between the adolescent and adult fast bowlers, with a greater proportion of adults having larger dominant side QL muscles, whilst the adolescent bowlers had asymmetries that were fairly evenly distributed between both sides of the spine. As discussed in Chapter 6, these differences may be an indication that the adults were professional players and likely to have higher lifetime bowling workloads, compared to the adolescents who were more likely to be involved in more than one sporting activity, which could influence their paraspinal muscle development. The increased bowling loads would most likely accelerate the expected muscle hypertrophy from asymmetrical activity (bowling). Perhaps the development of asymmetry in post adulthood reflects other musculoskeletal developments that occur around 25 years of age and appear to be protective from certain injuries such as lumbar bone stress injuries. Future research should be aimed at determining how bowling technique, workloads and age affect QL muscle hypertrophy Aim 5 Investigate the association between paraspinal muscle asymmetries and lumbar spine injuries in cricket fast bowlers There was no association between large QL asymmetries and lumbar spine injury in either adolescent or adult fast bowlers in this thesis (Chapters 5 and 6). This was contrary to earlier reports from Engstrom et al. (2007) in adolescent and Hides et al. (2008) in adult fast 194

196 bowlers, but confirmed the results of Ranson et al. (2006) who reported no link between QL asymmetry and injury. The differences in results between previous studies were discussed at length through the thesis with measurement methods likely to be responsible for some of the differences, although bowling technique and workloads, which may also be responsible, were not considered in any of the studies. Future research needs to take consideration of these factors as QL hypertrophy is likely to relate to a combination of technique and workload. Quadratus lumborum asymmetry may be a surrogate measure of the combination of these two known and modifiable risk factors. 7.2 Other findings The aims of the thesis were targeted towards reducing the high injury rates in cricket fast bowlers. There were some findings from this thesis that were not part of the aims that also have potential importance in future injury prevention. First, the link between BMI and lumbar bone stress injury in the adolescent fast bowlers in Chapter 5 was an indication that developmental factors may be involved in the development of this injury. This is particularly important the bowlers were at an age that was near puberty, where rapid musculoskeletal development is expected. Consideration needs to be given regarding the bowling workloads, preventative (strength / stability / flexibility) exercises and technique modification for adolescent bowlers as they may be more prone to lumbar bone stress injury during this rapid growth period. A second important finding was that all eight bowlers (four adolescent and four adult) with pre-season bone oedema on MRI went on to develop lumbar bone stress injuries during the following season. As reported in the thesis, this is similar to previous reports (Ranson, et al., 195

197 2010; Ranson, Burnett, King, O'Sullivan, et al., 2008) and needs to be examined further as it could be an important injury prevention tool, particularly as the genesis of lumbar bone injuries in unknown. It is possible that the MRI bone oedema may be an indication of the gradual development of bone stress during the bone strain part of the stress fracture continuum. It is possible that early identification may result in shorter recovery periods and reduction in the injury severity and prevalence rates (related to the long layout) following lumbar bone stress injuries. More extensive research is required to confirm these findings and recommendations. 7.3 Thesis Limitations There were number of limitations with the studies in this thesis. In particular, the injury surveillance study in Chapter 3 was limited to bowlers competing at international level only. Whilst provides a good injury profile of international bowlers, it made it more difficult to compare with other injury surveillance studies that included domestic matches. Additionally, bowling workloads were not factored into the injury analysis, which may have provided a better understanding of how they are associated with injury in that particular bowling cohort. A major limitation of the asymmetry studies in Chapter 5 and 6 was that bowling workloads and technique were not considered in the analysis. As discussed earlier in this chapter, these factors are likely to influence paraspinal development and could better explain the differences between these studies and past research. 196

198 7.4 Conclusion This thesis was the first to investigate the injury characteristics of elite players from Sri Lanka and demonstrated a similar pattern of fast bowling injuries compared their counterparts from other cricket playing nations. It highlights the vigorous nature of fast bowling and further explains why fast bowlers have the highest injury incidence, prevalence and severity. There was also confirmation that fast bowling results in asymmetrical paraspinal muscle development, with large QL asymmetries found in both adolescent and adult fast bowlers. Importantly, there was no association found between large QL asymmetry and lumbar bone stress injuries, which places doubt on the findings from some of the previous cricket related research that have found a strong links between QL asymmetry and injury. 197

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222 APPENDICES Appendix A International Cricket Council Member Countries and Membership Cricket is a summer sport played internationally by over 100 countries across the globe. As demonstrated in Table A1, there are three different tiers of membership (full member, associate member and affiliate member) with the sports governing body, the International Cricket Council. Membership status dictates the standard of tournaments that teams compete in and therefore level of professionalism of players, and is typically an indication of the popularity of cricket in each country. There are 10 full member countries of the International Cricket Council who compete at all major tournaments (Table A.2). International level players from the full member countries are generally full-time professionals. All full member countries play at least one home and one away series against each of the full member countries every two to four years. Every four years, the International Cricket Council conducts a major tournament, the ODI Cricket World Cup, which is considered to be the pinnacle of the ODI format of the game. The tournament lasts between six and eight weeks and involves all ten full member countries and up to four associate member countries. More recently, the shortest version of the game Twenty- Over (T20) cricket has emerged and International Cricket Council condoned World Cup events are staged approximately every two years. 221

223 Table A.1 List of International Cricket Council member countries (n=104) Full Members (n=10) Associate Members (n=34) Affiliate Members (n=60) South Africa (1909) West Indies (1926) Bangladesh (1977/2000) Australia (1909) England (1909) Zimbabwe (1981/1992) India (1926) New Zealand (1926) Pakistan (1953) Sri Lanka (1965/1982) Botswana (2001/2005) Argentina (1974) Hong Kong (1969) Fiji (1965) Belgium (1991/2005) Kenya (1981) Bermuda (1966) Kuwait (1998/2005) Japan (1989/2005) Denmark (1966) Namibia (1992) Canada (1968) Malaysia (1967) PNG (1973) France (1988/1998) Nigeria (1976/2002) Cayman Islands (1997/2002) Nepal (1988/1996) Germany (1991/1999) Tanzania (1966/2001) USA (1965) Singapore (1974) Guernsey (2005/2008) Uganda (1966/1998)* Thailand (1995/2005) Gibraltar (1969) Zambia (1989/2003) UAE (1990) Ireland (1993) Israel (1974) Cameroon (2007) Bahamas (1986) Afghanistan (2001) Cook Islands (2000) Austria (1992) Gambia (1976/2002) Belize (1997) Bahrain (2001) Indonesia (2001) Bulgaria (2008) Ghana (1976/2002) Brazil (2002) Bhutan (2001) Philippines (2000) Croatia (2001) Lesotho (2001) Chile (2002) Brunei (1992) Samoa (2000) Cyprus (1999) Malawi (1989/2003) Costa Rica (2002) China (2004) South Korea (2001) Czech Republic (2000) Mali (2005) Cuba (2002) Iran (2003) Tonga (2000) Estonia (2008) 222

224 Italy (1984/1995) Jersey (2005/2007) The Netherlands (1966) Scotland (1994)** Morocco (1999) Falkland Islands (2007) Maldives (2001) Vanuatu (1995) Finland (2000) Mozambique (2003) Mexico (2004) Myanmar (2006) Greece (1995) Rwanda (2003) Panama (2002) Oman (2000) Isle of Man (2004) Sierra Leone (1976/2002)* Peru (2007) Qatar (1999) Luxembourg (1998) St Helena (2001) Suriname(2002) Saudi Arabia (2003) Malta (1998) Swaziland (2007) Turks & Caicos Islands (2002) Norway (2000) Portugal (1996) Slovenia (2005) Spain (1992) Sweden (1997) Switzerland (1985) Turkey (2008) 223

225 Table A.2 List of full International Cricket Council member countries and year of inclusion Country Year of Test membership Year of One-Day Membership South Africa 1909 West Indies 1926 Bangladesh Australia 1909 England 1909 Zimbabwe India 1926 New Zealand 1926 Pakistan 1953 Sri Lanka

226 Appendix B The Fundamentals of Cricket The game is played by two teams of 11 players on an oval shaped grass field. At any given point one side is taking part in a batting innings while the other is in a bowling and fielding innings. During the batting innings, there are two players on the field. During the fielding innings, all 11 players are required to field with one player acting as a bowler. All 11 players are permitted to bowl and bat. The batsman s main role is to score as many runs as possible without being dismissed. The bowler s role is to dismiss the batsman in one of the 10 permitted methods in the laws of the game ("Laws of cricket," 2000) and restrict the batter from scoring runs with the assistance of the other 10 fielders. Central to the game is the cricket pitch, which is a rectangular area 3.05 meters wide and meters long that is placed in the centre of the oval field ("Laws of cricket," 2000). At the elite level, the pitch is special turf that takes weeks or months to prepare by using a variety of rollers to flatten and dry it out so that it will behave in consistent manner once the ball bounces on it. At each end of the pitch are set of wickets made of three cylindrical shaped pieces of timber known as stumps. The stumps are 71.1 centimeters high and all three together make the wickets centimeters wide ("Laws of cricket," 2000). One of the most common methods of dismissal for the batsman is when the bowler bowls the ball and strikes the stumps, so the batsman s primary sole is to defend his stumps using his cricket bat. The bat used is a piece of wood (usually English willow) that is 96.5 centimeters long and can be up to 10.8 centimeter wide ("Laws of cricket," 2000). Additionally, the batsman s role is strike the ball to different areas of the field and score runs by running to the other end of the pitch before the fielding team can throw the ball on to the wickets. At all times, there is one batsman at the batting end of the pitch and striking the ball (known as the striker ), whilst the other batter (known as the non-striker ) is at the other end of the pitch 225

227 and ready to run when the striker hits the ball. The non-striker becomes the striker when he ends up at the batting end of the pitch. The bowlers deliver the ball within the permitted rules of the game from the bowling end of the pitch. The bowler is allowed to ball six consecutive deliveries before being relieved by another bowler from the other end of the pitch. Each of the six balls bowled by a bowler is known as an over. The number of overs permitted per team and per bowler is restricted in some forms of the game (to be described below). Additionally, the amount of overs bowled per hour and per game are set in the rules of cricket ("Laws of cricket," 2000). Each of the player positions has specific requirements within the team. Batsmen generally have designated positions in the batting order but this can be varied at any time to meet the team demands. Fielding positions are also somewhat assigned according to the player s attributes and abilities, and can change at any time during a game. Typically players are selected based on their ability to bat, bowl or wicket-keep. In the modern game, wicket-keepers tend to also be very proficient batsmen. The make-up of the team can tend to vary to suit the conditions of the playing pitch, the weather conditions, the outfield and opposition. Typically most teams have six batsmen, one wicket-keeper and four specialised bowlers. The number of fast and spin (slow) bowlers in team also varies according to the ground conditions and team strengths. Most teams will generally have three fast bowlers and one spin bowler but can vary to suit the team s needs and the playing conditions encountered. Slow (spin) bowlers deliver the ball at speeds ranging from kilometres per hour (kph). As there is an overlap in bowling speeds between slow and fast bowlers, the distinction between them is typically made the positioning of the wicket-keeper who is the equivalent to a baseball catcher. For slow bowlers, the wicket-keeper fields immediately behind the batsman s 226

228 wickets, but for a fast bowler the wicket-keeper will generally field between 3-20 metres behind the batsman s wicket. 227

229 Appendix C Cricket Specifics Playing Positions Like many other team sports, cricket has a variety of playing positions; however it is different to most other sports because the player positions are vastly different from each other. There are four main player roles (positions) in cricket that involve differing and specific physical demands. The four main player positions are bowler, batsman, wicket-keeper and fielder. There is great overlap in these positions as every player can have the opportunity to bat, bowl and field during the game. All players are fielders when they not batting or bowling. Most players specialize as batsmen, bowlers or wicket-keepers. Specialist batsmen typically comprise of six or seven team members who are expected to score the majority of the runs for the team. Similarly, there are usually four or five specialist bowlers who bowl the majority of the deliveries in each game. There are also some of players who are similarly proficient in batting and bowling who are known as all-rounders. Genuine allrounders are considered a rare and valuable commodity to the team, as they can add to the teams strength in both batting and bowling. The wicket-keeper is a specialised fielder who stands behind the wickets at the batsman s end of the pitch to receive any balls missed by the batter (similar to a baseball catcher) and usually field more balls than other players. The wicket-keeper is typically positioned immediately behind the wickets for slower bowlers and moves further away from wicket for faster bowlers. The speed at which the bowler delivers that ball, determines how far the wicketkeeper stands behind the wickets. The ball used in cricket is hard and made of cork and covered in shiny hard leather, weighing between grams. The hardness of the ball can cause injury if it strikes a 228

230 player, particularly at high speed. Batsmen are permitted to wear protective padding on their legs, chest, arms, groins and hands. They also wear protective helmets. Fielders generally have no protective padding unless they are fielding very close to the batsman. The wicket-keeper wears protective leg pads, a groin guard and gloves. Bowlers can be categorized as either fast (pace) or slow bowlers. All bowlers have a run-up that varies in length, and then deliver the ball from behind a line drawn on the pitch, 19 metres from the batsman s wicket. Fast bowlers have longer run-ups and deliver the ball at a higher velocity, generating greater ground reaction forces than slow bowlers (Portus, et al., 2004). At the elite level, bowling velocities for male adult fast bowlers typically range from (kph), whilst slow bowlers deliver the ball at kph. Most slow bowlers are as spin bowlers because as they use their wrist or fingers to impart spin on the ball to deceive the batmen in the air and once it lands on the pitch. For the purposes of this thesis, the definition of a slow bowler is a bowler who has the wicket-keeper is positioned immediately behind the wickets for the majority of the deliveries and all slow bowlers will be referred to as spin bowlers; whilst a fast bowler has the wicket-keeper standing away from the wickets irrespective of bowling speed. As there is overlap between the batting and bowling roles, for injury surveillance purposes, it is important to clearly define the roles. The definition of bowler for this thesis is a player who primarily selected in the team for his bowling ability and with a regular batting position in the last four places in the batting order. This is different to the definition proposed by Orchard et al. (2005) who defined a bowler as someone who bowls an average of more than five overs per game for two consecutive seasons (Orchard, et al., 2005). Batsmen are defined as players that are primarily selected in the team for their ability bat and are placed in the top seven 229

231 batting positions. Wicket-keepers are defined as such if they are selected in the team for that specific position in the field. Types of cricket Apart from the variety in playing roles, cricket is also different from many other sports as there are three main formats of the game that place different physical demands on the participants. The two traditional forms of cricket have been One-Day (OD) matches and First Class matches. One-Day games are played in a limited over format in a single day and classified as List A games when played by two national level teams, whilst One-Day International (ODI) games are played by international teams. First Class games are played with no restrictions on the number of overs bowled or batted and is played over three, four or five days. Test matches are a form of First Class games that are played over five days by two international teams that have been granted Test Status by the International Cricket Council. As discussed above, T20 cricket has also increased in popularity and become an important part of world cricket. At the elite level, the game is played at either national (Domestic T20 games) or international level (T20 Internationals) and thrives on a number domestic level competitions played around the world. The different formats have large variations in player exposure, with T20 games being played in approximately three hours, OD and ODI matches approximately seven hours and First Class matches ranging from 18 hours (three days of play), up to thirty hours (over five days) in Test matches. A key difference between the different formats of cricket is that there are no restrictions on the player workloads (and therefore possible exposure to injury) during Test matches, whereas T20 and OD matches have specific limitations on the number deliveries that are bowled, batted and fielded in each match. Therefore, the amount of time that players are in the field varies considerably between Test and limited over formats (T20 and OD games). It is therefore 230

232 plausible to expect that injury characteristics may differ with the difference in playing exposure between Test and limited overs matches. There are also other aspects of the different formats that may impact on injury rates. For instance, OD, ODI and T20 matches can be more frantic in nature, as the players try to maximise the number of runs scored in the limited number of deliveries allocated to them. This sometimes means that batters run harder between wickets in an attempt to score quickly. Similarly, the fielders may also play at a higher intensity to limit the amount of runs scored by the batters. In Test matches, there is generally less urgency to score runs quickly because there are no real limits to the number of deliveries faced by each team. Levels of cricket At the elite level, cricket is played both at national (domestic) and international level. Typically, national competitions are played between representative state / provisional / county teams over the summer or the drier times of the year and last up to six months. International tournaments are played amongst international teams throughout the year in different parts of the world and typically last anywhere from 10 days to four months. Each countries level (ODI or Test) of participation is dependent on the status they receive from the International Cricket Council. 231

233 Appendix D Fast Bowling Biomechanics and Techniques The fast bowling action is the sequence of movements that occur just before the ball is released at the delivery stride (Ranson, Burnett, King, Patel, et al., 2008). Each bowler has a unique bowling technique but it is generally accepted that there are four main bowling techniques: front-on, side-on, semi-open (semi-on) and mixed (Ranson, Burnett, King, Patel, et al., 2008). The different bowling techniques are defined by position of the feet, pelvis, trunk and shoulders during specific times during the delivery stride, using video or ideally threedimensional computer analysis (Ranson, Burnett, King, Patel, et al., 2008). Fast bowling can be broken down to number components that are inter-related and important for both performance and injury (Portus, et al., 2004). The main components are the run-up, the delivery stride and follow-through. The run-up is important as it allows bowlers to gain momentum required to deliver the ball at a desired velocity. The delivery stride begins with the final ground contact known as back-foot contact (BFC), then transition to front-foot contact (FFC) and ends with bowl release (Figure B.1). The greatest ground reaction forces occur during the period between FFC and ball release (Elliott, et al., 1986; Foster, et al., 1989).The followthrough begins at ball release, involves deceleration of the bowler until they come to a stop. Figure B.1 Description of BFC (left) and FFC. Drawing adapted from Portus et al. (2004) 232

234 Bowlers are categorised into the four bowling techniques based on the positions and movements that occur during the delivery stride. The four main bowling techniques are (adapted from Portus et al.2004): 1. Front-on technique (Figure B.2) involves the alignment of the pelvis and shoulders parallel to the batsman at back-foot contact (BFC). Figure B.2 Description of front-on bowling technique. Drawing adapted from Portus et al. (2004) 2. Side-on technique (Figure B.3) is the alignments of the bowler s shoulders and pelvis perpendicular to the batsman at BFC. Figure B.3 Description of side-on bowling technique. Drawing adapted from Portus et al. (2004) 233