Correlation of Glenohumeral Internal Rotation Deficit and Total Rotational Motion to Shoulder Injuries in Professional Baseball Pitchers

Transcription

1 Correlation of Glenohumeral Internal Rotation Deficit and Total Rotational Motion to Shoulder Injuries in Professional Baseball Pitchers Kevin E. Wilk,* yz DPT, PT, Leonard C. Macrina, yz MSPT, SCS, CSCS, Glenn S. Fleisig, z PhD, Ronald Porterfield, MS, ATC, Charles D. Simpson II, y DPT, CSCS, Paul Harker, ATC, Nick Paparesta, ATC, and James R. Andrews, z MD Investigation performed at Champion Sports Medicine, American Sports Medicine Institute, Birmingham, Alabama. Data collection conducted at the training facility of the Tampa Bay Rays baseball team Background: Glenohumeral internal rotation deficit (GIRD) indicates a 20 or greater loss of internal rotation of the throwing shoulder compared with the nondominant shoulder. Purpose: To determine whether GIRD and a deficit in total rotational motion (external rotation 1 internal rotation) compared with the nonthrowing shoulder correlate with shoulder injuries in professional baseball pitchers. Study Design: Case series; Level of evidence, 4. Methods: Over 3 competitive seasons (2005 to 2007), passive range of motion measurements were evaluated on the dominant and nondominant shoulders for 170 pitcher-seasons. This included 122 professional pitchers during the 3 seasons of data collection, in which some pitchers were measured during multiple seasons. Ranges of motion were measured with a bubble goniometer during the preseason, by the same examiner each year. External and internal rotation of the glenohumeral joint was assessed with the participant supine and the arm abducted 90 in the plane of the scapula, with the scapula stabilized anteriorly at the coracoid process. The reproducibility of the test methods had an intraclass correlation coefficient of.81. Days in which the player was unable to participate because of injury or surgery were recorded during the season by the medical staff of the team and defined as an injury. Results: Pitchers with GIRD (n = 40) were nearly twice as likely to be injured as those without but without statistical significance (P =.17). Pitchers with total rotational motion deficit greater than 5 had a higher rate of injury. Minor league pitchers were more likely than major league pitchers to be injured. However, when players were injured, major league pitchers missed a significantly greater number of games than minor league pitchers. Conclusion: Compared with pitchers without GIRD, pitchers with GIRD appear to be at a higher risk for injury and shoulder surgery. Keywords: prevention; range of motion; overuse injuries; overhead athlete The overhead throwing motion generates tremendous demands on the glenohumeral joint at excessively high angular velocities. Shoulder internal rotation (IR) during *Address correspondence to Kevin E. Wilk, DPT, PT, Champion Sports Medicine, 805 St Vincent s Drive, Suite G100, Birmingham, AL ( KWilkpt@hotmail.com). y Champion Sports Medicine, Birmingham, Alabama. z American Sports Medicine Institute, Birmingham, Alabama. Tampa Bay Rays, St Petersburg, Florida. Presented at the 34th annual meeting of the AOSSM, Orlando, Florida, July The authors declared that they had no conflicts of interest in their authorship and publication of this contribution. The American Journal of Sports Medicine, Vol. 39, No. 2 DOI: / Ó 2011 The Author(s) a pitch is the fastest human movement recorded, and it occurs in excess of 7250 degrees per second. 12,13 The shoulder torque generated is approximately 60 Nm near the instant of maximal external rotation (ER). From repetition of this torque, the typical pitcher exhibits an excessive amount of ER of the glenohumeral joint. These repetitive torques and motions on the shoulder joint complex may contribute to the high injury rate in professional baseball. Conte et al 8 reported that 28% of all injuries sustained to professional baseball pitchers occurred at the shoulder joint. McFarland and Wasik 15 reported that upper extremity injuries in collegiate baseball players accounted for 75% of the time lost from the sport due to injury, with the pitcher being the most commonly injured player (69%). The most common injury cited was rotator cuff tendinitis. Shoulder injuries in pitchers are more common than in position players. 8,15 329

2 330 Wilk et al The American Journal of Sports Medicine Figure 1. Total rotational motion concept: the assessment of external rotation (ER) and internal rotation (IR) at 90 of abduction (ER 1 IR = total rotational motion). Greater ER and less IR is shown in (A) than in (B), but the total rotational range of motion (ER + IR) is equal in both. Reprinted with permission from Wilk KE, Meister K, Andrews JR. Current concepts in the rehabilitation of the overhead throwing athlete. Am J Sports Med. 2002;30(1): The disparity between IR of the dominant and nondominant shoulder has recently received increased attention from numerous clinicians. 5,7,10,11,24 This disparity, evidenced as less IR on the throwing shoulder, has been referred to as GIRD (glenohumeral IR deficit). GIRD, as defined by Burkhart et al, 5 is a loss of IR of the throwing shoulder of 20 or more as compared with the nonthrowing shoulder. Some clinicians have suggested GIRD as a cause of specific shoulder injuries. 6,7 Wilk et al 26 proposed the total rotational motion (TRM) concept, where the amount of ER and IR at 90 of abduction are added and a TRM arc is determined (Figure 1). The authors reported that the TRM in the throwing shoulders of professional baseball pitchers is within 5 of the nonthrowing shoulder. 26 Furthermore, the authors suggested that a TRM arc outside the 5 range may be a contributing factor to shoulder injuries. Although these proposed theories exist, the concepts are based on anecdotal experience and not published scientific data. The purpose of this study was to prospectively assess glenohumeral joint rotational motion, the difference in bilateral TRM, and how these factors correlate with injury risks. The ultimate goal was to correlate the findings to shoulder injuries in professional baseball pitchers each year during a 3-year period within the same professional baseball organization. MATERIALS AND METHODS Participants The study was conducted over 3 competitive seasons, from the beginning of 2005 to the end of Shoulder measurements were taken during spring training physical examinations. There were 170 pitcher-seasons included 13 pitchers had their passive range of motion (PROM) assessed in 3 consecutive seasons; 25 pitchers had it assessed in 2 consecutive seasons; and 81 had it assessed only once. Thus, there were 170 total measurements taken on the 122 pitchers who met the inclusion criteria. All participants were pain-free and asymptomatic at the time of testing. Exclusion criteria included anyone with a prior shoulder surgery within 2 years and any player who was unable to participate in daily spring training activities. Of the 170 pitcher-seasons, 126 involved right-handed pitchers and 44 involved left-handed pitchers. The average years of professional baseball experience was 5.2. Table 1 presents a description of the patient characteristics. Testing Procedure TABLE 1 Participant Characteristics a Age, y No. of right-handed pitcher-seasons 126 No. of left handed pitcher-seasons 44 Years of professional experience Height, cm Mass, kg a N = 170 pitcher-seasons. Glenohumeral joint PROM was assessed by the same examiners each year. Shoulder ER and IR was assessed at 90 of abduction and in the scapular plane by 1 examiner (K.E.W.) while another examiner (L.C.M.) measured the

3 Vol. 39, No. 2, 2011 Glenohumeral Internal Rotation Deficit and Total Rotational Motion 331 Figure 2. A, passive assessment of glenohumeral external rotation range of motion at 90 of abduction and 10 of horizontal adduction (scapular plane) with a bubble goniometer. B, assessment of glenohumeral internal rotation range of motion performed with stabilization of the scapula. The scapular coracoid process is palpated by the thumb, and the fingers are placed over the body of the scapula posteriorly. PROM with a bubble goniometer. During the ER and IR PROM assessment, the scapula was stabilized by 1 examiner (Figure 2). 18,27 The examiner passively moved the extremity to end range (point where end feel is perceived), and that position was held as the goniometer was aligned and read. For shoulder IR, a combination of end feel, palpation of the coracoid process, and visualization of compensatory movement was used to determine the end range of motion (ROM). The extremity was rotated until the participant s coracoid was felt rising into the examiner s thumb; motion was stopped when this movement occurred. To avoid altering the normal glenohumeral arthrokinematics, the humeral head was not manually stabilized. 27 The examiner performing the PROM assessment and end feel assessment had 25 years of clinical experience, including 19 years of experience performing spring training physicals for professional baseball players. A standard goniometer with an attached customized bubble inclinometer was used to ensure proper perpendicular alignment of the goniometer to the ground. For all shoulder measurements, the axis of the goniometer was positioned over the olecranon process, with the stationary arm of the device perpendicular to the ground and with the moveable arm aligned along the ulna to the ulnar styloid process. 19,27 All measurements were taken before any exercise, warm-up, or throwing activities. This testing procedure was utilized in a recently published article by Wilk et al. 27 Reliability A pilot study was previously performed to assess the intratester reliability of the goniometric methodology of this study. Ten asymptomatic men (mean age, 28.3 years; height, 180 cm; weight, 88 kg) were measured once in both positions for ER and IR PROM by the same examiners used in the current study. Both measurements were repeated on 5 consecutive days to assess intratester reliability. The order of tests performed was randomized, and all participants refrained from participating in any overhead throwing activities during the testing period. To examine the test-retest reliability, intraclass correlation coefficients were calculated on shoulder ER and shoulder IR using data collected in the pilot study. Singlemeasure intraclass correlation results were.81 for shoulder IR and.87 for shoulder ER. Wilk et al 27 reported that the highest intratester reliability for measuring IR was with scapular stabilization, at.62, compared with.51 when humeral head stabilization was employed. Injury Assessment and Classification All shoulder injuries were assessed by the head athletic trainer and the team physician (minimum of 12 years of professional baseball experience) of each club. For the minor league teams, the injuries were assessed, diagnosed, and classified by the head athletic trainer and physician of that team. The specific injuries (differential diagnosis, days on the disabled list, days unable to compete, and surgeries) were all recorded by each team s medical staff. Before each game, the head athletic trainer determined the player s status, which was defined as able to play, limited play, or unable to play. Unable to play referred to a player who was unable to play in that game because of shoulder injury or shoulder pain. Limited play referred to a player who had to leave the game because of injury. For the purpose of this study, players unable to play and players who experienced limited play were defined as being

4 332 Wilk et al The American Journal of Sports Medicine injured. The number of days on the disabled list was recorded but not used for data analysis owing to the inherit inconsistencies seen in that type of classification. If a player left the team for any reason (trade, released, retired, etc), every attempt was made to locate and contact that player to determine any injury occurrence or subsequent surgery. Study Design Participants were determined to have exhibited GIRD if their throwing shoulders displayed a 20 or more loss of IR compared with their nonthrowing shoulders. In addition, anyone who had a deficit of TRM more than 5 for his dominant shoulder (in comparison with his nondominant shoulder) was considered to exhibit a significant deficit in TRM. 26 The players IR deficit and TRM deficit values were analyzed relative to shoulder injuries occurring in the season that followed the measurements. Statistical Analysis Statistical analysis was performed with SPSS 11.5 (SPSS Inc, Chicago, IL). Ranges of motion were compared between dominant and nondominant shoulders using paired t tests (P \.05). Fisher exact tests were performed to identify any significant associations (P \.05) between GIRD and shoulder injury, and TRM deficit and shoulder injury. RESULTS TABLE 2 Range of Motion Comparisons a Dominant Nondominant External rotation, Internal rotation, Total rotational motion a In degrees. Each row, P \.001. Descriptive statistics for the 170 pitcher-seasons demonstrated average ERs (at 90 of shoulder abduction) of and on the dominant and nondominant sides, respectively. The mean dominant IR with the scapula stabilized was , whereas the mean nondominant IR was The TRM (ie, ER 1 IR) was and on the dominant and nondominant sides, respectively. A statistically significant difference was found between dominant and nondominant shoulders in IR, ER, and TRM (P \.001) (Table 2). During the 3 competitive seasons under study, there were 40 pitchers with GIRD, of whom 11 developed an injury requiring missed playing time. Also, of the 170 pitcher-seasons noted during the study, 33 injuries (30 players) resulted in a total of 1529 missed games. Injured pitchers had a slightly higher IR deficit ( ) than noninjured pitchers ( ), but this difference was not significant (P =.46). Twenty-eight percent (11 of 40) of the pitchers with GIRD were injured, whereas 17% (22 of 130) without GIRD were injured; however, this was not statistically significant (P =.17; odds ratio = 1.9, 95% confidence interval = 0.8 to 4.0). Thirteen percent (12 of 92) of the pitchers with TRM deficit less than or equal to 5 were injured, whereas 27% (21 of 78) of the pitchers with a TRM deficit greater than 5 were injured. Therefore, pitchers with a TRM difference greater than 5 were more likely to be injured (odds ratio = 2.5, 95% confidence interval = 1.1 to 5.3; P =.03). Of the 37 injuries reported, 29 (78%) occurred in pitchers whose dominant-arm TRM was greater than 176 ; 6 injuries (16%) occurred in pitchers whose TRM was less than 176 ; and 2 pitchers (5%) sustained injuries with a TRM of 176. There were no significant associations between IR difference and age (P =.504), height (P =.977), weight (P =.460), or years of experience (P =.924). A comparison was performed using independent-sample t tests to compare major league to minor league pitchers. No significant difference existed between major and minor leaguers IR difference (P =.81) or TRM difference (P =.58). A significant relationship between pitching level and shoulder injury existed (P =.04). Minor league pitchers were 2.5 times more likely to become injured (odds ratio = 2.5, 95% confidence interval = 1.1 to 5.6) than major league pitchers. However, when injured, a major league pitcher missed a greater number of games (P =.04). Major league pitchers missed games per injury, whereas minor league pitchers missed only games per injury. DISCUSSION Because of the repetition of such high forces generated during the throwing motion, the overhead throwing athlete can exhibit numerous and significant adaptations. Some of the most common adaptations are seen at the glenohumeral joint. Most throwers exhibit an obvious motion disparity whereby ER is excessive and IR is limited at 90 of abduction. 1,3,4,9,14,16,26 The loss of IR has been reported in the literature by numerous authors. There have been numerous proposed reasons for the motion adaptations, which include osseous adaptations (retroversion) 9,20-22 and soft tissue adaptations (capsular 5,25 and muscular 3,23,26 ). Reinold et al 23 reported that following a pitching performance, there is a loss of glenohumeral joint IR of 9.5 that lasts for 24 hours. Burkhart et al 5 suggested that GIRD is due to posterior capsular tightness. They concluded that stretching is the most appropriate treatment to address the IR deficit, and they recommended a posterior capsular release, should an aggressive stretching program not improve IR PROM. Borsa et al 3 documented that pitchers exhibit greater posterior translation than anterior References 1, 2, 4, 9, 14, 17, 21, 22, 25.

5 Vol. 39, No. 2, 2011 Glenohumeral Internal Rotation Deficit and Total Rotational Motion 333 TABLE 3 Risk Factors Associated With Shoulder Injury Pitchers Who Were Injured, % Risk Factor With Risk Factor Without Risk Factor Odds Ratio (95% Confidence Interval) P Total rotational motion deficit greater 27 (21 of 78) 13 (12 of 92) 2.5 (1.1, 5.3).03 than 5 Glenohumeral internal rotation deficit 28 (11 of 40) 17 (22 of 130) 1.9 (0.8, 4.2).17 (internal rotation deficit 20 ) Minor leaguer 27 (28 of 104) 13 (9 of 70) 2.5 (1.1, 5.6).04 translation. Furthermore, they reported that some individuals with very small amounts of IR PROM exhibited significant posterior glenohumeral laxity on objective testing. They proposed that the loss of IR was due to muscular tightness and humeral head retroversion and not posterior capsular tightness. Crockett et al 9 and others documented greater retroversion in the throwers dominant shoulders compared with their nondominant shoulders. Thus, if the loss of IR is due to osseous adaptation and muscular tightness, a stretching program directed toward the posterior rotator cuff muscles appears most appropriate to treat GIRD. In this study, pitchers exhibited greater glenohumeral ER and less IR on the throwing side compared with the nonthrowing side, which is consistent with previous research. 1,4,9,16,26 Furthermore, the average TRM was within 5, as reported by Wilk et al 26 in a previously published article. In this study, the mean TRM of the dominant shoulder was and on the nondominant side, Also in this study, the pitchers dominant shoulder IR was approximately 47.5 when the scapula was stabilized. In a previous study, we reported that the IR motion of the dominant shoulder was approximately 61 ; however, end ROM was noted when compensatory scapular motion was detected with visual inspection only. We have found that the most reliable method of assessing IR PROM in the throwing shoulder occurs when the scapula is stabilized at the coracoid process. This study also examined the relationship between (1) age and years of experience and (2) shoulder ROM, GIRD, and TRM. No significant correlation was noted between age and IR difference (P =.66) or between years of experience and IR difference (P =.87). Interestingly, the professional baseball team that we studied represents a young average age of the pitchers on staff. Of the 30 organizations in professional baseball, this organization is the sixth youngest (mean age of the team, 27.9 years; the pitching staff, 25.3 years). We wonder if the results would change if we studied a team with the oldest mean age (30.8 years) in Major League Baseball. There appears to be an increasing concern regarding the correlation between sustaining a shoulder injury and the loss of IR and GIRD. 5-7 To our knowledge, this is the first published study examining prospective PROM assessment and shoulder injuries in professional baseball pitchers during multiple seasons. We found that pitchers with GIRD exhibited almost twice the risk of sustaining a shoulder injury than pitchers without GIRD. Burkhart et al 5 reported that a side-to-side difference of 20 or greater resulted in greater susceptibility to injury. In this study, we found that injured players had a mean GIRD of Of 40 pitchers with GIRD, 11 were injured. Of the 130 shoulders without GIRD, 22 were injured. Of the pitchers with GIRD, 7% (3 of 40) underwent arthroscopic procedures to debride the rotator cuff and glenoid labrum. None received a posterior capsular release. Conversely, of the 130 pitcher-seasons without a case of GIRD, only 4 players underwent a shoulder arthroscopy. Although not included in this study, 5 players underwent elbow surgery during this time frame (4 ulnar collateral ligament reconstructions). Of the 5 players who had elbow surgery, 3 had GIRD. The TRM concept has been discussed by several authors. 11,16,26 This study is the first to examine the relationship between TRM and shoulder injuries. Pitchers whose TRM comparison was outside the 5 acceptable difference range exhibited a 2.5-times greater risk of sustaining a shoulder injury. In sum, 92 shoulders had TRM within the 5 range, and 78 shoulders had TRM outside the 5 range. 26 Furthermore, of the 37 injuries, 29 (78%) were sustained in throwers whose TRM was greater than 176. Stretching to increase IR PROM, thereby treating the GIRD, may result in an increase of TRM greater than 176 or outside the 5 acceptable window, compared with the contralateral shoulder. We believe that this may lead to an increased risk of injury because of the increased demands on the dynamic and static stabilizers surrounding the shoulder joint. Further research is needed to expose these effects on shoulder injuries. We believe that TRM is a valuable assessment tool and an important component in PROM assessment of throwers. This should be incorporated into the thrower s shoulder examination to determine if a ROM discrepancy is present in the athlete. An analysis of shoulders that exhibited GIRD and TRM differences was performed with respect to shoulder injury. We found no significant relationship (P =.130) between GIRD with TRM differences and missed games/surgeries. Pitchers with a TRM deficit greater than the 5 window (Table 3) were 2.5 times more likely to be injured (P =.03). Clinically, we believe that pitchers with GIRD and

6 334 Wilk et al The American Journal of Sports Medicine TRM differences outside the 5 window are at greater risk of injury. We examined the effect of having GIRD and a TRM deficit greater than 5 and noted only a trend (P =.09) in which this subgroup demonstrated a 2.2 times increased risk of injury. In this study, those clinical observations were possibly not substantiated because of the relatively low number of injuries and the total number of players involved throughout the 3-year study. Further research is needed to examine this relationship. In this study, only 13 of the 40 pitchers that exhibited GIRD were followed by the athletic training staff the following year or tracked during the time frame of this study ( ). Of the 13 who were tracked, 11 were successfully treated by the athletic training staff. We believe that this point is important most pitchers who exhibit GIRD can be successfully treated for a loss of IR PROM with an effective stretching program. To emphasize this point, we have developed a stretching and ROM program to treat pitchers with GIRD before they sustain an injury, in hopes of preventing occurrence. This stretching program is part of the pitcher s in-season and off-season training program. Two of 3 pitchers who exhibited GIRD in back-to-back seasons had shoulder surgery, and the third missed approximately 10% of the season because of elbow complaints. In this study, we noted a 62% reduction in all pitchers with GIRD from the 2006 season to the 2007 season. Furthermore, the 2007 season had the fewest injuries and the least amount of games missed. Anecdotally, we have noticed a reduction in GIRD in players from year to year. We believe that this is due to the greater recognition of GIRD as part of the spring training physical examination and to the more effective treatment strategies. We have incorporated this as a part of our spring training physical examination: If a player exhibits GIRD and/or a TRM difference greater than 5, he is placed on a supervised daily stretching program for the remainder of the season to eliminate the GIRD PROM deficits. In addition, caution is taken to not exceed 176 of TRM in the throwing shoulder. Limitations of the Study We believe that the relatively small sample size of injuries and total pitcher-seasons throughout the 3 seasons may have affected the overall power of the data. Also, pitchers are often traded from one organization to another, which makes it difficult to locate them regarding their injuries, surgeries, or missed games. We made every attempt possible to locate every player to update his medical status. In this study, only 36 shoulders were able to be evaluated for 2 or more seasons, because of trades, roster changes, and so forth. We believe that this is a significant limitation of this study. Another concern was the classification system used to determine an injury by the athletic trainers at each level. We relied on the team s medical staff to accurately recognize and record the injuries. As such, players may not report an injury, they may be misdiagnosed, or they may not be diagnosed at all by the medical staff. We debated on what to consider an injury. We concluded that any pitcher missing a game because of a shoulder complaint was considered unable to participate and thus classified as injured. Further studies are needed to control for these variables and thus confirm or refute our original findings. CONCLUSION Based on the results, a trend may exist in professional baseball pitchers with GIRD in that they have a higher risk of shoulder injuries. Also, in this study, pitchers with a TRM deficit greater than 5 had a significantly higher injury rate that resulted in missed playing time. The medical provider should consider these factors when determining the long-term prognosis of the pitchers. ACKNOWLEDGMENT We acknowledge the contributions of Mark Vinson, ATC, Kathleen M. Devine, DPT, MPH, Kim Suarez-Terrell, MSPT, Cristina Brassil, MSPT, and Christopher Arrigo, MSPT, ATC, for their extensive assistance in data collection and support. Furthermore, a special thank you to the Tampa Bay Rays baseball organization for its total support and commitment to this project. Without it, this project would not have been possible. REFERENCES 1. Bigliani LU, Codd TP, Connor PM, Levine WN, Littlefield MA, Hershon SJ. Shoulder motion and laxity in the professional baseball player. Am J Sports Med. 1997;25(5): Borsa PA, Dover GC, Wilk KE, Reinold MM. Glenohumeral range of motion and stiffness in professional baseball pitchers. Med Sci Sports Exerc. 2006;38(1): Borsa PA, Wilk KE, Jacobson JA, et al. Correlation of range of motion and glenohumeral translation in professional baseball pitchers. Am J Sports Med. 2005;33(9): Brown LP, Niehues SL, Harrah A, Yavorsky P, Hirshman HP. Upper extremity range of motion and isokinetic strength of the internal and external shoulder rotators in major league baseball players. Am J Sports Med. 1988;16(6): Burkhart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: spectrum of pathology. Part I: pathoanatomy and biomechanics. Arthroscopy. 2003;19(4): Burkhart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: spectrum of pathology. Part II: evaluation and treatment of SLAP lesions in throwers. Arthroscopy. 2003;19(5): Burkhart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: spectrum of pathology. Part III: the SICK scapula, scapular dyskinesis, the kinetic chain, and rehabilitation. Arthroscopy. 2003;19(6): Conte S, Requa RK, Garrick JG. Disability days in major league baseball. Am J Sports Med. 2001;29(4): Crockett HC, Gross LB, Wilk KE, et al. Osseous adaptation and range of motion at the glenohumeral joint in professional baseball pitchers. Am J Sports Med. 2002;30(1): Dines JS, Frank JB, Akerman M, Yocum LA. Glenohumeral internal rotation deficits in baseball players with ulnar collateral ligament insufficiency. Am J Sports Med. 2009;37(3): Ellenbecker TS, Roetert EP, Bailie DS, Davies GJ, Brown SW. Glenohumeral joint total rotation range of motion in elite tennis players and baseball pitchers. Med Sci Sports Exerc. 2002;34(12):

7 Vol. 39, No. 2, 2011 Glenohumeral Internal Rotation Deficit and Total Rotational Motion Fleisig GS, Andrews JR, Dillman CJ, Escamilla RF. Kinetics of baseball pitching with implications about injury mechanisms. Am J Sports Med. 1995;23(2): Fleisig GS, Barrentine SW, Escamilla RF, Andrews JR. Biomechanics of overhand throwing with implications for injuries. Sports Med. 1996;21(6): Johnson L. Patterns of shoulder flexibility among college baseball players. J Athl Train. 1992;27(1): McFarland EG, Wasik M. Epidemiology of collegiate baseball injuries. Clin J Sport Med. 1998;8(1): Meister K. Injuries to the shoulder in the throwing athlete. Part one: Biomechanics/pathophysiology/classification of injury. Am J Sports Med. 2000;28(2): Meister K, Day T, Horodyski M, Kaminski TW, Wasik MP, Tillman S. Rotational motion changes in the glenohumeral joint of the adolescent/little League baseball player. Am J Sports Med. 2005;33(5): Morrissey D, Morrissey MC, Driver W, King JB, Woledge RC. Manual landmark identification and tracking during the medial rotation test of the shoulder: an accuracy study using three-dimensional ultrasound and motion analysis measures. Man Ther. 2008;13(6): Norkin C, White DJ. Measurement of Joint Motion: A Guide to Goniometry. 2nd ed. Philadelphia, PA: Davis; Osbahr DC, Cannon DL, Speer KP. Retroversion of the humerus in the throwing shoulder of college baseball pitchers. Am J Sports Med. 2002;30(3): Pieper HG. Humeral torsion in the throwing arm of handball players. Am J Sports Med. 1998;26(2): Reagan KM, Meister K, Horodyski MB, Werner DW, Carruthers C, Wilk K. Humeral retroversion and its relationship to glenohumeral rotation in the shoulder of college baseball players. Am J Sports Med. 2002;30(3): Reinold MM, Wilk KE, Macrina LC, et al. Changes in shoulder and elbow passive range of motion after pitching in professional baseball players. Am J Sports Med. 2008;36(3): Torres RR, Gomes JL. Measurement of glenohumeral internal rotation in asymptomatic tennis players and swimmers. Am J Sports Med. 2009;37(5): Tyler TF, Nicholas SJ, Roy T, Gleim GW. Quantification of posterior capsule tightness and motion loss in patients with shoulder impingement. Am J Sports Med. 2000;28(5): Wilk KE, Meister K, Andrews JR. Current concepts in the rehabilitation of the overhead throwing athlete. Am J Sports Med. 2002;30(1): Wilk KE, Reinold MM, Macrina LC, et al. Glenohumeral internal rotation measurements differ depending on stabilization techniques. Sports Health. 2009;1(2): For reprints and permission queries, please visit SAGE s Web site at