DIFFERENCES IN GLENOHUMERAL INTERNAL ROTATION DEFICIT BETWEEN FEMALE AND MALE COLLEGE ATHLETES

Transcription

1 Glenohumeral Internal Rotation Deficit 13 DIFFERENCES IN GLENOHUMERAL INTERNAL ROTATION DEFICIT BETWEEN FEMALE AND MALE COLLEGE ATHLETES ERIKA WORTHLEY 1, J.P. BARFIELD 1 1 Sports Medicine Program, Department of Health and Human Performance, Radford University, Radford, VA USA ABSTRACT Worthley, E., Barfield, J.P. Differences in Glenohumeral Internal Rotation Deficit between Female and Male College Athletes. Journal of Undergraduate Kinesiology Research 2015;10(2): Purpose: Glenohumeral Internal Rotation Deficit (GIRD) is the standard measure of shoulder injury risk in athletes. Although male overhead athletes (e.g., baseball players) have a documented increased risk of GIRD and associated injury risk, little research has examined this variable in female athletic populations. Therefore, the purpose of this study was to compare GIRD in baseball and softball players at the collegiate level over the course of a non-competitive season. Methods: GIRD was assessed on 57 NCAA athletes (MAge = yrs, MExperience = yrs, n = 38 baseball, 19 softball players) on two occasions, pre-fall and post-fall season. We calculated GIRD as a fifteen-degree difference between the dominant and non-dominant shoulder internal rotation measurements. IRB approval and participant consent was obtained prior to the study. Results: At Pre-Fall, 10% of baseball players demonstrated GIRD. Fortunately, zero percent demonstrated GIRD at Post-Fall, indicating a major risk reduction. Twenty-six percent of softball players were positive for GIRD at baseline measurements. The same percentage demonstrated GIRD at follow-up; however, two players decreased their risk whereas two different players demonstrated GIRD. Conclusion: Results indicate that GIRD may be a greater concern for female overhead college athletes compared to males. This conclusion is supported by the higher percentage of players at risk for shoulder injury (through presence of GIRD) and the reduced ability to decrease player risk across a sport season. Key Words: Overuse Injury, Shoulder Injury, Rotator Cuff, Retroversion

2 Glenohumeral Internal Rotation Deficit 14 INTRODUCTION Due to the overwhelming forces and stress put on the glenohumeral joint during overhead activities (e.g., baseball, softball, tennis, volleyball), athletes in these sports are at high risk for injury. For example, approximately 45% of all baseball injuries occur to the upper extremity, with 15% of those injuries due explicitly to throwing. And despite the media attention given to elbow surgeries, shoulder injuries are more common than elbow in this population (1). Injury risk to the shoulder can be attributed to the demands of overhead sports. Unlike other activities, overhead sports require a balance between both glenohumeral joint mobility and stability that in turn leads to a hypermobile or hypomobile shoulder when compared to non-overhead athletes (2). Altered mobility results from the excessive forces from repetitive throwing on the shoulder girdle, shoulder joint, and surrounding soft tissue (3). As a result, overhead throwers (e.g., baseball and softball players) often demonstrate a chronic increase in external rotation and decrease in internal rotation in their dominant throwing arm compared to their non-dominant (4). Glenohumeral Internal Rotation Deficit (GIRD) is the term used to describe this phenomenon and is considered a risk factor for shoulder injury in overhead athletes (5). Causes of GIRD There are a number of theories that try to explain why GIRD occurs. Borsa and colleagues suggested that posterior joint structure contractures are the primary origins. While it is uncertain which posterior structures are to blame, these authors believe muscle shortening/thickening (i.e., contractures) are a chronic adaptation to repetitive overhead activity that reduces the potential for internal rotation (2). This perspective is supported by thicker posterior capsules seen through arthroscopy in patients with GIRD (6) and a correlation between posterior shoulder tightness and loss of internal rotation (7). The ability of a posterior capsule stretching protocol to regain range of motion also appears to support this hypothesis (8). As an alternative to muscle shortening or tightening, Crocket et al. have suggested that humeral retroversion, or a chronic increase in external rotation due to repetitive overhead movements, ultimately limits internal rotation (9). Rather than the humerus being restricted from moving internally, this theory reflects anatomical changes in the bone and articulation site that limit the range of internal rotation as a consequence of more efficient external rotation. This outcome reflects a tissue adaptation rather than the aforementioned muscular restriction. A third possibility is that the extreme forces required to move the arm from full external rotation to full internal rotation result in overuse and altered mobility patterns in the glenohumeral joint (5). Influence of Age and Gender on GIRD Regardless of the cause, athletes become most susceptible to developing GIRD following puberty (10). Although trauma due to glenohumeral forces can begin at a young age (11), research documents that GIRD is more common in athletes between the ages of when compared to athletes between the ages of 8-12 (3). Whereas the influence of age on GIRD has been well studied, the influence of gender has not. This discrepancy is problematic because it is unclear if female overhead athletes have less, equal, or greater shoulder injury risk than their male counterparts. Higher injury risk in females could result from the significant glenohumeral mobility differences between genders. Hypermobility is considered a risk factor for injury and is more common in females, which puts females, theoretically, at a heightened risk of developing GIRD (12). However, risk of GIRD may be lower in females due to mechanical differences between sports. Softball pitchers receive the greatest shoulder joint stress during the shoulder flexion acceleration phase of throwing, a

3 Glenohumeral Internal Rotation Deficit 15 concentric muscle activity generally associated with lower injury risk (11). Baseball pitchers, on the other hand, sustain a tremendous amount of stress on the shoulder joint during the deceleration phase of throwing (i.e., the posterior musculature contracts eccentrically to slow the arm), an action associated with greater injury potential. However, the potential risk difference could be offset by the fact that baseball pitchers are monitored by pitch counts but softball players are not. This procedural discrepancy typically results in softball pitchers throwing a high numbers of pitches every day (13). It is not surprising, then, that softball pitchers have reported 45% of time-loss injuries due to overuse injuries to the shoulder and/or elbow (14). It seems plausible that female overhead athletes could demonstrate a higher prevalence of GIRD and therefore be at greater risk for shoulder injury despite similar throwing mechanics at many positions (e.g., catcher). Research Problem Overhead sports for females have become increasingly more popular in the past decade. In fact, female participation in softball has increased by 16%. The increase in participation, combined with the upper extremity accounting for 40-52% of injuries in softball specifically, signifies the importance of testing female athletes for GIRD (15). It is clear that female overhead athletes are anatomically different from male overhead athletes and may be as, or more, susceptible to develop GIRD (16). Currently, there is very little research on this topic in female athletes, and even less in female softball players. Therefore, the purpose of this study was to compare the prevalence of GIRD in softball players compared to their male counterparts to determine if female overhead athletes are at a higher injury risk. Since players are most susceptible to GIRD following adolescence, we chose to compare college-level athletes. METHODS Participants Thirty-eight National Collegiate Athletic Association (NCAA) baseball players and nineteen NCAA softball players from two different schools were included in this study. The participants were members of existing baseball and softball teams at their respective schools. Each subgroup of participants included both pitchers and position players and descriptive statistics on player demographic data are included in Table 1. All participants provided written informed consent, and Radford University s Institutional Review Board approved the study. Instruments A goniometer was used to measure internal and external rotation of the shoulder. The participant laid supine on the table with their shoulder abducted to 90 degrees and their elbow flexed to 90 degrees. The same investigator measured internal and external rotation bilaterally, starting with the dominant arm. Before each measurement, the researcher ensured the participant s arm was in a neutral starting position. For the internal rotation measurements, participants were instructed to keep their shoulder on the table to minimize scapular movement. Procedures On the initial testing day, participants attended their regularly scheduled practice. Participants completed their typical stretching and warm-up protocol before measurements were taken. We began by measuring internal rotation on the dominant arm, followed by external rotation on the dominant arm, and repeated those measurements in that order on the non-dominant arm. Each measurement was taken once. We used the measurements obtained to calculate GIRD by determining the difference between the maximal internal rotation of the non-dominant arm and dominant arm. Measurements were taken with the first week of the fall practice season (Pre-Fall) and the last week of the fall practice season (Post-Fall).

4 Glenohumeral Internal Rotation Deficit 16 Data Analysis Descriptive statistics on internal and external rotation were computed after each data collection session. A fifteen-degree internal rotation difference between the dominant and non-dominant throwing shoulder was used to classify a player as positive for GIRD. A ten-degree difference between the non-dominant and dominant shoulder internal rotation measurement classified the player as at risk. The prevalence of male and female players with GIRD was determined for Pre-Fall and Post-Fall. Additionally, the percentage of players whose GIRD status changed across the season was compared. A final analysis of the prevalence of GIRD by position was also determined for each sport at the conclusion of each data collection period. RESULTS Our Pre-Fall measurements identified a total of nine players with GIRD (15%), while the post-fall measurements only identified five (8%). For Pre-Fall, five softball players, totaling twenty-six percent of the team, demonstrated GIRD. At Post-Fall measurements, five softball players, which again totaled twenty-six percent of the team, were identified as having GIRD. Two of the five athletes that tested positive for GIRD at Pre-Fall did not show any indication of GIRD at the post-fall measurements. However, two of the five athletes that tested positive for GIRD at Post-Fall had developed GIRD during the fall season. Of the female athletes that tested positive at either the Pre- Fall or Post-Fall measurements, one was a pitcher, one was a catcher, two were infielders, and three were outfielders. Four baseball players (10%) demonstrated GIRD at Pre-Fall. At Post-Fall, however, zero baseball players had results that were indicative of GIRD. Therefore, all four male athletes who initially demonstrated having GIRD had improved range of motion sufficient to reduce their injury risk. Of the male athletes that tested positive for GIRD at the Pre-Fall measurements, three were pitchers and one was an outfielder. Range of motion data for Pre-Fall and Post-Fall for both females and males are presented in Table 1. Table 1. Demographic and Range of Motion Data (M ± SD). Variable Females Males Age (yrs) 19 ± 1 19 ± 1 Experience (yrs) ± 2 Pre-Fall Season Dominant Shoulder Internal Rotation 63 ± ± 11 External Rotation 75 ± ± 13 Non-Dominant Shoulder Internal Rotation 69 ± ± 10 External Rotation 74 ± ± 11 Internal Rotation Difference 6 ± 11 5 ± 10 Post-Fall Season Dominant Shoulder Internal Rotation 66 ± ± 9 External Rotation 81 ± ± 15 Non-Dominant Shoulder Internal Rotation 75 ± ± 10 External Rotation 76 ± ± 11 Internal Rotation Difference 8 ± 13 2 ± 7

5 Glenohumeral Internal Rotation Deficit 17 DISCUSSION The prevalence of GIRD was higher in softball players than baseball players in the current study, indicating a greater risk of shoulder injury. Females also had more difficulty improving their range of motion when compared to male athletes. Position played did not affect the likelihood of testing positive for GIRD in softball players. This outcome was surprising because softball catchers make the most overhand throws, an average of 53 per game, compared to infielders, which typically only throw four to six times a game (11). One would expect a higher different injury risk due to athlete demands but this was not the case in the current study. The baseball results indicated that pitchers might be at much higher risk for GIRD. Baseball pitchers being at high risk is no surprise based on previous research. Softball players being at higher risk, however, is novel to the literature. Increased shoulder injury risk in females could be the result of a few factors. For example, softball players do not have any pitching restrictions like baseball (13). Females also have more laxity in their joints, which could result in different throwing mechanics when compared to males. Unfortunately, the results of this study are limited. The results come from a small sample size of two teams. The participants who were on the same team had similar practice and exercise regimens. In order for the results to be more generalizable, the study should be repeated with a larger sample size and greater variety of training/conditioning programs. Additionally, all participants were collegiate athletes, so a comparison to high school athletes, professional athletes or non-athletes may be more beneficial. Fortunately, the results of this study lead to many new opportunities for research. Future research could focus on high school and collegiate athletes to determine which age group is at a higher risk. A longitudinal study may also be beneficial in determining when GIRD typically becomes an issue. Our study only examined changes during the off-season and a study examining changes during a competitive season may have distinct results. Another beneficial study may be to compare GIRD in female and male volleyball, tennis and swimming athletes. In these three sports, males and females both participate in the exact same manner, whereas in softball, the overhead performance characteristics can differ (e.g., overhead versus underhand throwing). Testing the effects of posterior capsule stretching would also be beneficial, and could especially be useful in a longitudinal study to see if it helps eliminate GIRD. CONCLUSION Results indicate that GIRD, and associated injury risk, may be more prevalent among female overhead college athletes compared to male overhead college athletes. This conclusion is supported by the higher percentage of players at risk for shoulder injury, through presence of GIRD, and the reduced ability to decrease player risk across an off-season sports season. ACKNOWLEDGEMENTS The authors would like the coaches and players who volunteered to participate in this study. Address for Correspondence: Barfield, J.P., D.A. Department of Health and Human Performance. Radford University, Radford, VA, USA, Phone (540) ; FAX (540) ; . abarfield@radford.edu.

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7 Glenohumeral Internal Rotation Deficit 19 Disclaimer The opinions expressed in the Journal of Undergraduate Kinesiology Research are those of the authors and are not attributable to the Journal of Undergraduate Kinesiology Research, the editorial staff or Western State Colorado University