Injuries in the New Zealand semi-professional rugby league competition

Injuries in the New Zealand semi-professional rugby league competition D A King MHealSc 1, T J Gabbett PhD 2 1 Emergency Department Hutt Valley District Health Board Lower Hutt NEW ZEALAND 2 Brisbane Broncos Rugby League Club Red Hill Queensland AUSTRALIA Correspondence to: Doug King Emergency Department Hutt Valley District Health Board Private Bag Lower Hutt NEW ZEALAND Tel: +64 4 566 6999 ext 8118 Email: douglas.king@huttvalleydhb.org.nz ABSTRACT Objective: While the incidence of rugby league injuries has been investigated, the majority of studies have been limited to single clubs. The purpose of this study was to document and identify injuries sustained in the 2005 New Zealand semi-professional rugby league competition, the Bartercard Cup. Methods: Eight teams competing in the 2005 Bartercard Cup competition were studied using a prospective observational field based study. All injuries sustained in the competition were recorded on a standardized injury reporting form. Injuries were categorized according to type, site, cause and severity of the injury. Injuries were recorded as rate per 1000 playing hours and were classified by severity according to the number of matches missed. Results: The overall incidence of injury for the competition was 115 per 1000 playing hours while the incidence of injuries resulting in missed matches was 78 per 1000 playing hours. Forty-seven percent (54 per 1000 playing hours) of all injuries sustained occurred in the lower limbs. Most injuries occurred in the tackle situation (95 per 1000 playing hours). The shoulder was the single most common injury site (16 per 1000 playing hours). Strains were the most common injury type (28 per 1000 playing hours). Conclusion: The results of this study demonstrate that the incidence of injury in New Zealand semi-professional rugby league players is similar to that previously reported in Australian semi-professional rugby league players. Further research investigating risk factors for tackling injuries is warranted in an attempt to reduce the incidence of ball carrier and tackler injuries in rugby league. Keywords: injury incidence, semi-professional, rugby league 6 NZJSM

INTRODUCTION Rugby league is an international collision sport played by junior, amateur, semi-professional and professional players. 1-4 The game requires participants to be involved in physically demanding activities such as running, tackling, passing and sprinting. 5,6 These activities are often interspersed with short bouts of low intensity activity such as jogging and walking. 5, 6 Exposure to physical collisions and tackles is common in rugby league and musculoskeletal injuries occur as a consequence of participation in the sport. 5,7,8 There have been several studies of the incidence of injury in rugby league in amateur 1,9-11 and professional 12-14 levels of participation, but only one in semiprofessional 5 participation. Professional rugby league has reported a 1.3 to 2.2 fold higher injury incidence than amateur participation. 5 The study on semiprofessional participation reported a higher injury incidence than either amateur or professional participation injury rates. 5 To date, few studies have investigated the incidence of injury in 10, 11 New Zealand rugby league players. These studies have reported injury rates in the range of 24.5 11 to 278 10 per 1000 playing hours, depending on the injury definition used. However these studies are dated with no recent studies completed in New Zealand rugby league matches. The Bartercard Cup was introduced in 2000 and is New Zealand s semiprofessional competition. The competition consists of 12 teams from throughout New Zealand. The competition has resulted in several players being promoted towards the professional level and has proven successful for rugby league in the country. The purpose of this study was to investigate the incidence, site, nature, cause,and severity of injuries sustained during match participation in the 2005 New Zealand Bartercard Cup competition. METHODS A prospective observational field based study was undertaken to document the incidence of injuries in matches occurring over the 2005 New Zealand rugby league Bartercard Cup competition. This involved data collection on 240 rugby league players from eight of the 12 competing teams. All teams were invited to participate in the study and eight teams agreed and consented to data being collected. Ethical approval was obtained from the University of Otago Ethics Committee. Team trainers recorded all injuries on a standardized injury reporting form regardless of severity (see Figure 1). The injury reporting form was modified to meet the requirements of the study but utilized the format previously established in studies on rugby league injuries. 5,15 The participating teams competed in a home and away competition format. All player matches were played over 80 minutes duration (40 minutes per half) and under the limited 12 person interchange rule. Three of the participating teams were eligible for the final series with one participating team going through to the grand final match. The competing teams had their own trainers that were allowed access to the field of play. All team trainers ORIGINAL ARTICLE were nationally accredited in injury prevention, assessment and management through the New Zealand Rugby League Academy of Excellence. Each of the participating team trainers recorded their own injury data on a standardized injury reporting form (see Figure 1) 2, 5, 16, 17 and this was entered into a central database. Definition of Injury The definition of injury utilized for this study was any pain or disability suffered by a player during a match that required advice and/or treatment. 2-4,9,17,18 Injuries were classified anatomically according to the player position at the time of the injury occurring, the injury site, 4,16,17 the nature of the injury, 4,16,17 and the causative mechanism. 4,5,17 All injuries reported to have occurred during the matches were recorded regardless of severity. However, injuries were also classified according to the number of matches missed as a result of the injury. 2,5,12,17,19 Statistical Analysis Over the duration of the competition, 136 matches were studied. All matches were 80 minutes (1.33 hours) in duration with an overall injury exposure of 2351 playing hours. The expected injury frequency was calculated as described by Hodgson- Phillips et al. 12 (see Table 1). A one sample chi-squared (X 2 ) test was used to determine whether the observed injury frequency was significantly different from the expected injury frequency. Data are reported as means and 95% confidence intervals (CI). 20 Significant p values reported in the text are less than 0.0001 if they are not specifically stated. TABLE 1: Injury statistics per month for rate, man hours, per game, player appearances and per minutes played. April May June July August September No injuries observed 51 40 55 56 59 9 No injuries expected 47.6 47.6 47.6 63.5 59.6 4.0 Injury rates per 1000 h 122.9 96.4 132.5 101.2 113.7 260.3 played 95% CI* (93.4-161.7) (70.7-131.4) (101.8-172.6) (77.9-131.4) (88.1-146.8) (135.4-500.2) Number games played 24 24 24 32 30 2 Exposure hrs 415.0 415.0 415.0 553.3 518.7 34.6 Man hrs per injury 8.1 (7.2-9.2) 10.4 (9.2 11.7) 7.5(6.7-8.5) 9.9 (8.8-11.1) 8.8(7.8-9.9) 3.8(3.4-4.3) (95% CI) Total number injuries 2.1 (1.9-2.4) 1.7 (1.5-1.9) 2.3(2.0-2.6) 1.8 (1.6-2.0) 2.0(1.7-2.2) 4.5(4.0-5.1) per game (95%CI) Player appearances 6.1 (5.4-6.9) 7.8 (6.9-8.8) 5.7(5.0-6.4) 7.4 (6.6-8.4) 6.6(5.9-7.4) 2.9(2.6-3.3) per injury (95% CI) Game minutes played 37.6 (33.4-42.4) 48.0 (42.6 54.1) 34.9(31.0-39.3) 45.7 (40.6-51.5) 40.7(36.1-45.8) 17.8(15.8-20.0) per injury (95% CI) *Confidence Intervals Vol 36 No 1 2009 7

RESULTS Over the period of the study a total of 270 injuries were recorded. The overall injury incidence was 115 per 1000 playing hours. The incidence of injuries that resulted in missed matches was 78 per 1000 playing hours. Player Position Player position injury incidences for both overall injuries and injuries causing missed matches are shown in Table 2. The fullback recorded more total injuries (149 per 1000 playing hours) for the competition while props recorded more injuries resulting in missed matches (111 per 1000 playing hours). When comparing the injury incidence between forwards and backs there was no statistical difference observed (X 2 =2; df=1; p=0.19). 8 NZJSM

TABLE 2: Injuries by player position for the 2005 New Zealand Bartercard cup competition. ORIGINAL ARTICLE TOTAL INJURIES MISSED MATCH INJURIES No Rate* 95% CI % No Rate* 95% CI % Fullback 27 149.3 (102.4 217.7) 10.0 18 99.5 (62.7 157.9) 8.7 Wing 15 41.5 (25.0 68.8) 5.6 11 30.4 (16.8 54.9) 5.4 Centre 48 132.7 (100.0 176.1) 17.8 35 96.7 (69.5 134.8) 14.7 Stand-Off 16 88.5 (54.2 144.4) 5.9 9 49.8 (25.9 95.6) 4.9 Halfback 18 99.5 (62.7 157.9) 6.7 11 60.8 (33.7 109.8) 6.0 Prop 50 138.2 (104.8 182.4) 18.5 32 88.5 (62.6 125.1) 12.5 Hooker 25 138.2 (93.4 204.5) 9.3 20 110.6 (71.3 171.4) 10.9 Second Row 49 135.4 (102.4 179.2) 18.1 33 91.2 (64.9 128.3) 15.2 Loose Forward 22 60.8 (40.0 92.4) 8.1 15 41.5 (25.0 68.8) 8.2 *Rate expressed per 1000 playing hours. CI, confidence intervals. Site of Injury The shoulder was the most common injury site for both total (16 per 1000 playing hours) and missed matches (13 per 1000 playing hours) (see Figure 2). Forty seven percent of the injuries recorded occurred to the lower limbs for both total (54 per 1000 playing hours) and missed match (37 per 1000 playing hours) injuries. The head and neck incurred 20.0% of total (23 per 1000 playing hours) and 17.9% of missed match (14 per 1000 playing hours) injuries. FIGURE 2: Site of injuries with 95% confidence intervals for overall injuries (A) and injuries resulting in missed matches (B) for the 2005 New Zealand Bartercard Cup competition. Vol 36 No 1 2009 9

Injury sites differed between forwards and backs for both total and missed match injuries. Forwards recorded significantly more total (22 per 1000 playing hours vs. 10 per 1000 playing hours; X 2 =5; df=1; p=0.0224) and missed match (18 per 1000 playing hours vs. 8 per 1000 playing hours; X 2 =3; df=1; p=0.242) injures to the shoulder while backs recorded more total (13 per 1000 playing hours vs. 9 per 1000 playing hours; X 2 =0.9; df=1; p0.342) and missed match (10 per 1000 playing hours vs. 6 per 1000 playing hours; X 2 =0.7; df=1; p=0.4156) injuries to the thigh. Nature of Injury The nature of the injuries for total and missed matches is shown in Figure 3. Strains occurred more commonly for both total (28 per 1000 playing hours) and missed match (23 per 1000 playing hours) injuries. Bruises were more commonly reported for forwards than backs (33 per 1000 playing hours vs.21 per 1000 playing hours; X 2 =3; df=1; p=0.0801). Fractures (10 per 1000 playing hours vs. 5 per 1000 playing hours; X 2 =2; df=1; p=0.1249) and dislocations (10 per 1000 playing hours vs. 6 per 1000 playing hours; X 2 =2; df=1; p=0.2030) also featured highly among forwards. Cause of Injury Most injuries occurred in the tackle situation (95 per 1000 playing hours) (see Figure 4). There were no statistically significant differences between the ball carrier and the tackling player (51 per 1000 playing hours vs.45 per 1000 playing hours; X 2 =0.43, df=1, p=1.0) for the incidence of injuries. FIGURE 3: Nature of injuries with 95% confidence intervals for overall injuries (A) and injuries resulting in missed matches (B) for the 2005 New Zealand Bartercard Cup competition. 10 NZJSM

FIGURE 4: Cause of overall injuries (A) and injuries resulting in missed matches (B) with 95% confidence intervals for the 2005 New Zealand Bartercard Cup competition. TABLE 3: Severity of injury for the 2005 New Zealand Bartercard Cup competition. FORWARDS BACKS No Rate* 9%% CI No Rate* 95% CI Transient 46 42.4 (31.7 56.6) 40 31.6 (23.2 43.1) Minor 61 56.2 (43.7 72.2) 55 43.4 (33.4 56.6) Moderate 24 22.1 (14.8 33.0) 20 15.8 (10.2 24.5) Major 15 13.8 (8.3 22.9) 9 7.1 (3.7 13.7) *Rate expressed per 1000 playing hours. CI, confidence intervals. Severity of Injury There were more minor injuries recorded (49 per 1000 playing hours) than transient (37 per 1000 playing hours), moderate (19 per 1000 playing hours) and major (10 per 1000 playing hours) injuries (see Table 3). Time of Injury There was a significant difference between the first and second halves of matches (90 per 1000 playing hours vs. 138 per 1000 playing hours; X 2 =13, df=1, p=0.0004) for total match injuries incidence (see Figure 5). More injuries occurred in the third quarter of matches for both total (168 per 1000 playing hours) and missed match (117 per 1000 playing hours) injuries. When comparing the first with the second half of the competition season (including the final series), there was a statistical significance observed for total injuries (114 per 1000 playing hours vs.118 per 1000 playing hours; X 2 =8, df=1, p=0.005), and injuries resulting in missed matches (77 per 1000 playing hours vs. 81 per 1000 playing hours; X 2 =5, df=1, p=0.027) with more injuries occurring in the first half of the competition season (see Table 4). Vol 36 No 1 2009 11

FIGURE 5: Match time by quarters with 95% confidence intervals for overall injuries (A) and injuries resulting in missed matches (B) for the 2005 New Zealand Bartercard Cup competition. TABLE 4: Early and late season injuries for the 2005 New Zealand Bartercard Cup competition. TOTAL INJURIES Forwards Backs No Rate* 95% CI No Rate 95% CI Early Season 83 130.0 (104.8 161.2) 75 100.7 (80.3 126.3) Late Season 63 143.5 (112.1 183.7) 49 95.7 (72.3 126.6) MISSED MATCH INJURIES Forwards Backs No Rate* 95%CI No Rate 95%CI Early Season 58 90.9 (70.2 117.5) 49 65.8 (49.7 87.0) Late Season 42 95.7 (70.7 129.5) 35 68.4 (49.1 95.2) *Rate expressed per 1000 playing hours. CI, confidence intervals. 12 NZJSM

Home vs Away A total of 68 home and 68 away matches were played. There was no statistical difference between total home and away venue injuries recorded (117 per 1000 playing hours vs. 113 per 1000 playing hours; X 2 =0.1, df=1, p=0.81) and missed match (75 per 1000 playing hours vs. 82 per 1000 playing hours; X 2 =0.4, df=1, p=0.55) injury incidences. DISCUSSION The purpose of this study was to investigate the incidence, site, nature, cause, and severity of injuries sustained during match participation in the 2005 New Zealand Bartercard Cup competition. The overall incidence of injury in the present study (114.8 per 1000 playing hours) was lower than previously reported for amateur (161 per 1000 playing hours), 9 semi-professional (825 per 1000 playing hours) 5,21,22 and professional (346 per 1000 playing hours) 12 rugby league players using an identical injury definition. In addition, when using an identical injury definition to a previous study of semiprofessional rugby league players, the incidence of total injuries was noticeably less (115 per 1000 hours vs. 825 per 1000 hours) but by measuring missed matches, the studies were shown to be similar in injury incidence (78 per 1000 playing hours vs. 68 per 1000 playing hours). 5 This similar missed match injury incidence reinforces the need for a standardized injury definition in rugby league. R e c e n t a t t e m p t s t o e s t a b l i s h a standardised injury definition in rugby league 23 have seen some, but not all researchers agree. 23, 24 Some were not in favour of a definition that was all encompassing and enabled non time-loss injuries to be recorded preferring to record time-loss injuries alone. 24,25 Although time loss injuries enable a more consistent inter study comparison to be conducted, studies have reported that non time-loss injuries can account for between 85% 26 to 93% 27 of match injuries, and up to 98% 27 of training injuries. The inclusion of non time loss injuries has been reported to bias the reported data towards non time loss injuries and, as a result of this bias, head and neck injuries make up a large proportion of the total injuries in rugby league. 28 Further development of an injury definition is necessary to enable a unified approach to the identification of the injury rate for all researchers in rugby league injury epidemiology. The timing of the New Zealand competition was similar to other competitions - being held during the autumn, winter and spring seasons. Although previous studies have identified a progressive increase in the injury incidence throughout the season, 21 the variations observed throughout this competition warrant further exploration. These variations are: (1) the higher initial injury incidence (123 per 1000 playing hours) at the beginning of the season (April); (2) the increased injury incidence in the mid-season period (June), and (3) the increased injury incidence at the end of the season (September). The higher initial injury incidence at the beginning of the competition season identified in this study may be related to p o o r m a t c h f i t n e s s a n d p l a y e r conditioning. 9 A study on risk factors for injury in rugby league 21,29 have identified that players with less than 18 weeks of training, low sprint speed and a low estimated maximal aerobic power are at an increased risk of injury. No data was obtained on the anthropometric and physiological characteristics of participants, nor on the amount of precompetition training the participants completed. Previous playing experience and previous injury history were also shown to be risk factors for subsequent injuries occurring. 21,29 A recommendation for subsequent studies in rugby league would be to include this data in the collection. The increased incidence of injury in the mid-season period may be due to accumulation of micro-trauma and residual fatigue. 9 Semi-professional participants have been reported as having a higher fitness level than amateur participants but lower skill levels than professional players. 5,21,22 The higher fitness level may result in a higher playing intensity and, in some team situations, decreased rest and recovery between match and training sessions. This decreased recovery has been shown to result in accumulation of micro trauma from the physical nature of contact ORIGINAL ARTICLE sports. 30 As well residual fatigue, associated with a limited recovery time between successive matches, may also compromise the musculoskeletal system of the participant. This may account for the number of tackle related injuries recorded. The increased fitness and strength of semi-professional participants may influence the intensity of the tackle, but the reduced skill level may influence the type of injury that occurs as a result of the tackle. Combined with residual fatigue and accumulated micro trauma, the risk of an injury occurring would be increased at this level of participation. The increased injury incidence at the end of the season may be attributed to the ensuing finals series of the competition. 5 Some studies have reported higher injury rates at the end of the competition season suggesting changes in playing intensity at this stage of the competition. 5,31 The increased playing intensity may result in physiological demands being placed on the participant that are higher than the musculoskeletal system can tolerate. Gabbett 27 found a significant correlation (r=0.74) between match injury rates and match intensity in semi-professional participation. These findings would be expected as the intensity of the finals series approaches. Further studies are warranted to determine the appropriate match intensity level required to enable teams to be competitive but not place the participants at risk of excessive physiological demands. The overall lower injury incidence, when compared to the other semi-professional study, may be related to environmental and ground conditions on which matches were played. The Australian study was undertaken on teams playing in the New South Wales and Queensland environment where ground conditions are recorded as harder and temperatures warmer. 5 The softer ground conditions and cooler temperatures in New Zealand may have aided in reducing the overall injury incidence but may also have contributed to the types of injuries that were recorded. In support of this hypothesis, it has recently been found 32 that harder ground conditions and lower 365-day rainfall is associated with increased injury risk in rugby league. Vol 36 No 1 2009 13

CONCLUSION The finding that the majority of injuries occurred in the tackle is consistent with previous studies in amateur, 1 semi-professional 5 and professional studies. 13,14,33 The ball carrier recorded more injuries than the tackler which is similar to professional 13,14,33 and semiprofessional 5 studies. In contrast, in amateur rugby league players, the tackler has been shown to sustain more injuries than the ball carrier. 1 Previous studies have suggested that a greater emphasis on dominating the ruck and the introduction of the 10m rule 5,34 combined with low speed and maximal aerobic power 29 may explain the differences in injury incidence between semi-professional and amateur levels of participation, but additional aspects of the tackle also need to be considered. While the tackle is responsible for the majority of injuries in rugby league, there is no current research into the risk factors for tackle injuries in rugby league. Nor is there any published research on tackle types, height and sites in rugby league that result in injuries. Research is ongoing in this area but the results are unavailable at the time of this study being conducted (personal communication). Training activities designed to develop correct tackling technique may reduce the incidence of tackle-related injuries. 35,36 Participation in tackling technique training prior to and under fatigued conditions may assist in the reduction of tacklerelated injuries to both the tackler and the ball carrier 1,35,36, however, to date, no evidence exists to support or refute these potential injury prevention strategies. Further research investigating risk factors for tackling injuries is warranted in an attempt to reduce the incidence of tackle-related injuries in rugby league. Limitations The study was conducted on only eight of the 12 teams that participated in the 2005 Bartercard Cup competition despite all teams being invited to participate. Although this study is one of a few studies to report on multi-team participation, the study was only conducted on one competition season. As well the competition has now been discontinued and a further study at this level of competition is no longer available in New Zealand. Consequently the current study is limited to being just a snap shot of the competition and is unable to explore seasonal variations of semi-professional participation. Training participation and training injury incidence data were also not gathered as part of this study and this data may have been useful to identify rest and recovery between matches, the training injury incidence and injury type in comparison with other studies in rugby league. What is already known on this topic? Most rugby league studies use single teams or clubs to document injury rates. The incidence of injuries in semiprofessional rugby league is high What this study adds? This study is one of the few studies to utilize multiple teams to investigate the incidence of injury in rugby league. The incidence of missed match injuries is similar for semiprofessional participants compared to amateur and professional participants despite there being a difference in the overall injury incidence. Future Research Possible future areas of research identified are: Risk factor analysis of tackle related injuries Previous playing experience and injury history on participants in relationship to current and ongoing injury incidence Determination of the appropriate match intensity level required to enable teams to be competitive but not place the participants at risk of excessive physiological demands Multi team competition over consecutive seasons to enable identification of seasonal variations. 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