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The Relationship Between Glenohumeral Internal Rotational Deficits, Total Range of Motion, and Shoulder Strength in Professional Baseball Pitchers

Amin, Nirav H. MD; Ryan, John MD; Fening, Stephen D. PhD; Soloff, Lonnie PT; Schickendantz, Mark S. MD; Jones, Morgan MD

JAAOS - Journal of the American Academy of Orthopaedic Surgeons: December 2015 - Volume 23 - Issue 12 - p 789–796
doi: 10.5435/JAAOS-D-15-00292
Clinical Research Article
Free

Introduction: Although the lack of internal rotation (IR) and total range of motion (TRM) has been identified as a significant contributing factor of shoulder injuries, our goal was to determine whether a relationship exists between glenohumeral internal rotational deficits (GIRD), TRM, and shoulder strength in professional baseball pitchers. Our hypothesis was that GIRD with TRM differences within 5° will not lead to decreased shoulder strength; however, a shoulder with >5° of TRM difference with GIRD will lead to decreased shoulder strength.

Methods: The study was conducted over a 4-year period and included 193 major and minor league pitchers. All measurements were taken prior to the pitcher’s engaging in any baseball-related activities on the day of measurements. The entire measurement arc of passive range of motion (PROM), including external rotation (ER) and IR, was defined as the TRM. GIRD was defined as a loss of 25° or more of IR of the throwing shoulder compared with the nonthrowing shoulder. Shoulder strength measurements were obtained using a validated digital dynamometer with the arm in 90° of abduction and with the arm in 110° of flexion and 30° of abduction measured in pounds.

Results: The IR deficit was 5.89° (SD = 9.24°) in non-GIRD pitchers and 25.52° (SD = 4.35°) in GIRD pitchers (P > 0.001). The ER change was 124.08° (SD = 11.21°) in non-GIRD pitchers and 127.79° (SD = 9.15°) in GIRD pitchers. The total arc of motion was 179.54° (SD = 14.53°) in non-GIRD pitchers and 171.93° (SD = 12.34°) in GIRD pitchers (P > 0.001). The strength in the shoulder, measured with the arm in 90° of abduction, was 29.61 lb (SD = 4.76 lb) in non-GIRD pitchers versus 28.65 lb (SD = 4.81 lb) in GIRD pitchers. The strength with the arm in 110° of flexion and 30° of abduction was 29.43 lb (SD = 5.01 lb) in non-GIRD pitchers versus 28.13 lb (SD = 4.76 lb) in pitchers with GIRD (P = 0.043). Deficiencies in total arc of motion (P < 0.001) and shoulder strength (P < 0.043) were significantly associated with GIRD.

Discussion: In our evaluation of 193 pitchers examined during their preseason physical examinations, we identified a statistically significant association between decreased total arc of motion, decreased shoulder strength, and GIRD.

From the Loma Linda University Medical Center, Loma Linda, CA (Dr. Amin), The Ohio State University, Columbus, OH (Dr. Ryan), Case Western Reserve University School of Medicine, Cleveland, OH (Dr. Fening), the Cleveland Indians, Cleveland, OH (Mr. Soloff), and the Cleveland Clinic, Cleveland, OH (Dr. Schickendantz and Dr. Jones).

Correspondence to Dr. Amin: naminmd@gmail.com

Dr. Fening or an immediate family member serves as a paid consultant to or is an employee of and has stock or stock options held in Apto Orthopaedics. Dr. Schickendantz or an immediate family member serves as a paid consultant to or is an employee of Arthrex and serves as a board member, owner, officer, or committee member of the American Orthopaedic Society for Sports Medicine. Dr. Jones or an immediate family member serves as a board member, owner, officer, or committee member of the American Orthopaedic Society for Sports Medicine. None of the following authors or any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this article: Dr. Amin, Dr. Ryan, and Mr. Soloff.

Received June 06, 2015

Accepted October 01, 2015

Shoulder injuries are common in overhead sports such as baseball, tennis, and volleyball and are a particular concern in professional baseball pitchers. Conte et al,1 in a 2001 review of data obtained from the Major League Baseball disabled players lists, reported overall injury rates as high as 58 injuries per 100 participants.1 Of these injuries, the shoulder (27%) and elbow (22%) were the most common locations of injury. Pitchers made up a disproportionate percentage of those injured, comprising 48% of players on the disabled list.1

Although several different types of shoulder and elbow injuries occur in professional pitchers, including labral and rotator cuff pathology and injuries to the ulnar collateral ligament (UCL) of the elbow, predictors of these injuries are not well defined. The ability to identify those at high risk for developing future shoulder injuries would be a powerful tool for the physicians, trainers, and therapists caring for these athletes. By accurately predicting those who are susceptible to shoulder injury, injury prevention strategies might be more precisely and effectively developed. With shoulder injuries being the most common injury in pitchers, such strategies would be particularly useful.1,2

A substantial body of research has described the adaptive structural changes that occur in the dominant shoulder of overhead athletes in general and in baseball pitchers in particular.3 In 1969, King et al4 provided a description of adaptive changes in the dominant arms of professional baseball pitchers, including a nearly uniform increase in external rotation (ER) with a corresponding decrease in internal rotation (IR) at the glenohumeral joint, compared with the nondominant shoulder. In 2003, Burkart and colleagues5-7 described the mechanics of an overhead throwing motion, and the associated changes within the shoulder, leading to decreased IR of the shoulder, known as glenohumeral internal rotation deficit (GIRD). Dillman et al8 noted the amount of glenohumeral range of motion (ROM) at the late cocking phase of throwing a ball necessary to generate the high rotational forces needed for a pitcher. The IR deficit in GIRD is most commonly interpreted in relationship to the nondominant shoulder. The posteroinferior capsular tightness leads to GIRD and scapular dyskinesis in the dominant arm, which may play a substantial role in the pathologic cascade, culminating in the development of articular surface rotator cuff tears and tearing of the posterosuperior labrum. Furthermore, these athletes are susceptible to a muscular fatigue syndrome, the SICK (scapular malposition, inferior medial border prominence, coracoid pain and malposition, and dyskinesis of scapular movement) scapula syndrome. The IR deficit is addressed by stretching the posterior capsule. Since this original description, many studies have reported similar glenohumeral rotational changes in overhead athletes.9-20

A commonly used definition for clinically important or severe GIRD is an IR deficiency >20° to 25° compared with the nondominant shoulder.6 Importantly, GIRD has been described as one of the primary causes of shoulder injuries.7,21 In addition to assessing the GIRD, Wilk et al22 added the ER and IR at 90° of abduction to determine the total range of motion (TRM). Using the TRM, Wilk, et al22 recently noted that, in comparing the dominant to nondominant arm in pitchers, those with a difference >5° had a 2.5 times greater risk of sustaining a shoulder injury.

Although the lack of IR and TRM has been identified as a significant contributing factor of shoulder injuries,7,9-22 we prospectively studied shoulder strength, TRM, and GIRD, and how shoulder strength is related to GIRD and TRM. The goal of this study was to determine whether a relationship exists between GIRD, TRM, and shoulder strength in professional baseball pitchers. When assessing GIRD and TRM, our hypothesis was that GIRD with TRM differences within 5° will not lead to decreased shoulder strength; however, a shoulder with >5° of TRM differences with GIRD will lead to decreased shoulder strength, which may potentially be used by the medical staff as a baseline strength to help athletes avoid shoulder and elbow injuries in the upcoming season.

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Methods

The study was conducted over a 4-year period beginning in 2005 and ending in 2008. The shoulder measurements were taken during the annual entrance examination by the athletic training staff. Two hundred thirteen pitchers were studied, with 193 pitchers included in the study (both major and minor league pitchers), involving seven professional baseball teams from a single organization. As the inclusion criteria, all the pitchers were asymptomatic and pain-free at the time of testing. The exclusion criteria included any pitcher who had past shoulder surgery and any player who reported shoulder symptoms that had resulted in missed playing time within the past year.

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Examination

All measurements were taken before the pitcher’s engaging in any baseball-related activities on the day of measurements. One examiner assessed shoulder passive range of motion (PROM) at each training session. A goniometer technique was used by placing the fulcrum over the olecranon process. The scapula was stabilized during the PROM assessment (Figure 1). The TRM of the shoulder was examined by placing the patient supine, with the shoulder in 90° of abduction in the plane of the scapula, with the elbow flexed to 90°. The plane of the scapula was 10° to 15° anterior to the coronal plane. The scapula was stabilized during IR by palpation of the coracoid process, in which scapulothoracic contributions occur at the terminal motion of internal motion. When the scapula moved into protraction and/or anterior tilt, the IR measure was taken. The ER of the shoulder was measured with the shoulder in the plane of the scapula, with 90° of abduction, and slow passive ER was continued until resistance and movement of the scapula (ie, posterior tilt or retraction) was obtained. Wilk et al22 published a study looking at three methods of glenohumeral joint IR and reported that the C-shape stabilization (with the hand on the coracoid process) proved to be reliable in both intra-rater and inter-rater applications. Glenohumeral IR measurements differ depending on stabilization techniques; therefore, the C-shape stabilization technique was used to minimize the errors of measurement at the ends of ROM.

Figure 1

Figure 1

The entire measurement arc of PROM, including ER and IR, was defined as the TRM. GIRD was defined by Burkhart et al23 as a loss of 25° or more of IR of the throwing shoulder compared with the non-throwing shoulder. Shoulder strength measurements were obtained using a validated digital dynamometer (MicroFET 2 Manual Muscle Testing Handheld Dynamometer; Hoggan Scientific) with the arm in 90° of abduction (Figure 2), and with the arm in 110° of flexion and 30° of abduction (Figure 3) measured in pounds.

Figure 2

Figure 2

Figure 3

Figure 3

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Statistical Analysis

The statistical analysis was completed using Fisher exact tests to identify any significant associations (P < 0.05) between GIRD, TRM deficit, and shoulder strength. Calculations were performed using open source R software (http://www.r-project.org).

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Results

Pitchers determined to have GIRD were defined as having a difference in IR between the dominant and non-dominant arms of at least 25°. Subsequently, a difference of TRM >5° between the dominant and non-dominant shoulder was classified as a deficit in TRM. The pitchers with GIRD and TRM deficits together were compared with the pitchers with no GIRD and TRM to determine changes within the shoulder strength.

A total of 193 pitchers were examined for IR deficit, ER deficit, total arc of motion, and shoulder strength. The IR deficit in non-GIRD pitchers was 5.89° (standard deviation [SD] = 9.24°) and 25.52° (SD = 4.35°) in GIRD pitchers (P > 0.001). The ER change was 124.08° (SD = 11.21°) in non-GIRD pitchers and 127.79° (SD = 9.15°) in GIRD pitchers. The total arc of motion in the non-GIRD pitchers was 179.54° (SD = 14.53°) and 171.93° (SD = 12.34°) in GIRD pitchers (P > 0.001). The strength in the shoulder, measured with the arm in 90° of abduction, was 29.61 lb (SD = 4.76 lb) in non-GIRD pitchers versus 28.65 lb (SD = 4.81 lb) in GIRD pitchers. The strength with the arm in 110° of flexion and 30° of abduction was 29.43 lb (SD = 5.01 lb) in non-GIRD pitchers versus 28.13 lb (SD = 4.76 lb) in pitchers with GIRD, with a P value of 0.043 between the two groups of pitchers, using a linear regression model to determine whether deficiencies (in dominant and non-dominant arms) in shoulder total arc of motion and in shoulder strength measured in pounds by a shoulder and abduction predicted GIRD. Deficiencies in total arc of motion (P < 0.001) and shoulder strength (P < 0.043) were significantly associated with GIRD (Tables 1 and 2).

Table 1

Table 1

Table 2

Table 2

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Discussion

In our evaluation of 193 pitchers examined during their preseason physical examinations, we identified a statistically significant association between decreased total arc of motion, decreased shoulder strength, and GIRD.

The pitching motion is composed of a carefully orchestrated kinetic chain that transfers energy from the legs, up through the pelvis and trunk, into the upper extremity, and finally to the baseball. As energy is funneled from the trunk into the shoulder and elbow, these progressively smaller joints undergo tremendous stresses.24 During delivery of a pitch, as the point of maximum ER is reached, the shoulder experiences up to a 111 Nm IR torque and up to 1,090 N in compressive force across the glenohumeral joint, immediately after the ball is released.24,25 As pitchers repeat this sequence numerous times over the course of a contest, season, and career, anatomic changes occur in the shoulder to accommodate the chronic stress.24 In addition to the kinetic chain-of-energy transfer, the evaluation of the scapula is necessary to exclude diagnosis of scapular dyskinesis. Kinsella et al26 noted that protracted or excessive IR of the scapula leads to rotator cuff weakness, which causes a poor length-tension relationship of the rotator cuff complex. This is often seen because the origin of the rotator cuff complex is from the scapula.

Further evidence suggests that shoulder adaptive changes occur before skeletal maturity in throwing athletes.16,27,28 Meister et al16 measured shoulder IR and ER in 294 baseball players between the ages of 8 and 16 years and found significant differences in ER and IR between dominant and non-dominant arms. They noted that the total arc of motion decreased as age increased, with the most dramatic decrease occurring in 13- and 14-year-olds. They postulated that this loss of motion was a result of bone and soft-tissue adaptation, particularly in response to stress at the proximal humeral physis during throwing.16 Between the ages of 13 and 16 years, this physis undergoes rapid growth and may be particularly susceptible to the stress of throwing. Levine et al27 made similar observations in a study of pitchers across a wider age range (8 to 28 years old). Crockett et al11 reported that increased humeral head retroversion at least partially accounts for the highly consistent findings of increased ER and decreased IR in pitchers. The authors speculated that this osseous adaptation plays a central role in the development of GIRD and may confer a competitive as well as potentially protective advantage.11 Kinsella et al26 noted increased humeral retroversion changes of the thrower's arc of motion, with a gain in ER motion with a loss of IR motion. This increase allows the thrower’s shoulder to increase ER before the greater tuberosity engagement with the posterior superior labrum in the abduction ER position.26 The change in the arc of motion can lead to posterior cuff and labral pathology in throwers. Thomas et al29 also found increased retroversion of the humerus to lead to posterior capsular thickness or GIRD, which creates negative effects on the shoulder kinematics. The humeral retroversion leads to a loss of IR and a symmetric gain of the ER motion, in most cases with an arc loss of motion of 10° to 17°.29

While the studies described earlier support the theory of osseous adaptive changes to the shoulder in response to the demands of pitching in younger age groups, other researchers attribute changes in shoulder rotation to soft-tissue microtrauma and the gradual onset of a pathologic process, even after skeletal maturity. Burkhart et al6 postulated that the observed increase in ER and decrease in IR is primarily a result of repetitive microtrauma to and eventual stretching of the anterior capsule of the glenohumeral joint during the cocking phase of throwing. The subsequent acquired loss of IR arises from posteroinferior capsular contracture, which functions as the “essential lesion” in the development of GIRD. Tehranzadeh et al28 performed a retrospective review of magnetic resonance arthrograms in six professional pitchers who had presented with pain and reduced velocity and had been diagnosed with GIRD. They noted that posterior capsular thickening was a clear and consistent finding in all six patients. Associated lesions seen on imaging were partial undersurface rotator cuff tears and type 1 and 2 SLAP (superior labrum anterior-to-posterior) tears. Burkhart et al23 noted that professional throwers who were examined in the preseason with an IR rotation deficit >25° had a higher rate of shoulder difficulties during the upcoming season compared with the contralateral shoulder. Osseous as well as soft-tissue adaptations are likely both involved in the development of GIRD; however, the relative importance of each is unknown. Clabbers et al30 placed cadaver specimens in the late-cocking position after imbricating the posterior capsule to assess the relationship between posterior capsular tightness and changes in the glenohumeral relationship. The imbricated posterior capsule leads to relative posterior and superior migration of the humeral head. Huffman et al31 and Grossman et al32 found translation of the humeral head with posterior capsule tightness in addition to the anterior capsular laxity of the arm in the abduction ER position. The posterior inferior capsular contracture leads to an inferior tether that does not allow the dominant arm to achieve a full ER of the humerus. The subsequent results of the new center of rotation leads to an increased contact along the posterior cuff and labrum, leading to eccentric fiber failure and articular surface tearing. In contrast, Bailey et al33 found posterior rotator cuff stiffness to be the primary cause of ROM deficits with the baseball cohort. Within the two cohorts, baseball players with instrument-assisted soft-tissue mobilization with self-stretching noted a decrease in the posterior rotator cuff stiffness and an increase in ROM compared with the healthy baseball players. Harshbarger et al34 found a relationship between rotator cuff stiffness and strength. Similarly, this study found a loss of motion within the total arc led to a decrease in shoulder strength.

Despite the high prevalence of GIRD in professional baseball pitchers, a relatively small amount of research to date has focused on demonstrating a clear relationship between GIRD and shoulder injuries in pitchers and how progression of GIRD over time might increase the risk of injury. With an improved understanding of the unique adaptive anatomy in pitchers, it is easy to infer a causal relationship between GIRD and shoulder injury. Guney et al35 recently showed that the ratio of eccentric external rotator strength to concentric internal rotator strength in GIRD shoulders is lower than the ratio in shoulders without GIRD, and is a risk factor for shoulder injuries. However, the exact mechanism by which GIRD may lead to shoulder injury in pitchers is not well established. Furthermore, the specific subsets of this athletic population that is at greatest risk for injury are not known. Several associations between GIRD and shoulder injury in pitchers have been reported and suggest that GIRD plays an important role in the development of shoulder pathology. Burkhart and colleagues,5-7 in reporting on a series of 124 pitchers (professional, college, and high school) with arthroscopically proven type 2 SLAP lesions, found that all cases in the series had coexisting GIRD of at least 25°. Additionally, Verna36 followed 39 professional pitchers over a single season and found that 60% of the pitchers with a GIRD of 35° during spring training subsequently experienced shoulder problems severe enough to cause them to miss playing time during the season during the Professional Baseball Athletic Trainer Society Meeting (PBATS). In a study looking at a variable closely related to GIRD—total rotational arc of motion in the dominant shoulder—Ruotolo et al37 found that a history of shoulder pain correlated with a decreased total arc of motion as well as a decreased IR in collegiate baseball players. Recently, Wilk et al21 followed 92 pitchers with a TRM within 5° compared with 78 pitchers outside the 5° range and found a 2.5 times greater risk of shoulder injury. Furthermore, Wilk et al38 followed 122 professional pitchers over a 3-year span and found a trend (although not statistically significant) in which pitchers with GIRD and decreased TRM had a higher rate of shoulder injuries compared with pitchers without deficits. It is critical to note that the numbers were not clinically significant due to the low number of injuries and limited number of players available at a professional level. To our knowledge, the present study is the first study to demonstrate a relationship between GIRD, TRM deficits >5° (P < 0.001), and shoulder strength (P < 0.001). Because of the small sample size, clinical observations were based on the limited number of pitchers available during the 4-year window.

In our study, 165 pitchers who did not demonstrate GIRD had higher shoulder strength (29.61 [SD = 4.76]), and the abduction strength was 29.43 (SD = 5.01). The 25 pitchers with GIRD had lower shoulder strength (28.65 [SD = 4.81]), and the abduction strength was 28.13 (SD = 4.76), demonstrating a statistical trend (P < 0.043). The effects of the changes within the shoulder strength need to be further studied; however, players were closely supervised with daily stretching programs under the direct supervision of the athletic training staff to eliminate the GIRD and PROM deficits along with shoulder strength weakness. Another clinical observation is the loss in strength in pitchers demonstrating TRM >176°. Wilk et al38 and Wilk et al21 demonstrated a significantly higher rate of injuries in pitchers who had TRM >176° caused by increased demands on the dynamic and static stabilizers surrounding the shoulder joint; however, further biomechanics studies need to be performed.

Garrison et al39 recently compared the ROM of the shoulder and its relationship with UCL injuries. They found that a deficit in the TRM was associated with UCL tears in high school and collegiate athletes. However, they did not find a relationship with GIRD and UCL injuries. Wilk et al38 followed professional baseball players over an 8-year period, during which pitchers with a deficit >5° in total rotation in their throwing shoulder had a 2.6-fold greater risk for injury to the elbow.

In this study, a relationship was found between GIRD, TRM, and weakness in the shoulder strength. Considering the epidemic in elbow injuries over the course of the past year, analyzing the TRM, GIRD, and strength of the shoulder, may help clinicians create preventive protocols to put in place to reduce shoulder and elbow injuries. Trakis et al40 found that an increase in IR strength was associated with a decrease in supraspinatus strength. These findings were directly correlated with increased pain in the elbow and shoulder.40 Subsequently, Garrison et al41 noted that a higher statistical rate of baseball players with UCL tears had significant rotator cuff strength loss in their throwing arm in IR and ER compared with a healthy cohort. A future clinical study may analyze the relationship with the changes in TRM, GIRD, and shoulder strength and possible increases in stresses along the UCL in the elbow. In addition, assessing the changes in the kinematics at the shoulder and elbow related to decreased shoulder strength, GIRD, and TRM may allow medical staffs to pinpoint a level of strength loss leading to significant shoulder and elbow pathology.

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Limitations

The small number of professional baseball pitchers within one professional organization led to statistical challenges of the power of this study. Recognizing the limitations of this study, we feel that further studies accounting for playing time missed may provide clearer answers to the proposed effects of shoulder strength, GIRD, TRM and shoulder injuries. It may provide an insight for the medical staff to identify players at a higher risk of injury during the spring training examination and to create a threshold of shoulder strength to avoid risk of shoulder issues in the ensuing season.

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Conclusion

This is the first study to our knowledge to correlate the GIRD, TRM, and shoulder strength of baseball pitchers, which may lend credence to the fact that GIRD may be a response to the shoulder strength deficits rather than the cause of the injury. Irrespective, the effects of the shoulder strength deficits within the setting of GIRD and TRM may be helpful to a medical training staff to determine baseline shoulder strength and thus help avoid shoulder and elbow difficulty during the upcoming season.

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References

References printed in bold type are those published within the past 5 years.

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Keywords:

GIRD; total arc of motion; abduction strength; shoulder injury; internal rotation deficits

© 2015 by American Academy of Orthopaedic Surgeons