Professional Pitchers With Glenohumeral Internal Rotation Deficit (GIRD) Display Greater Humeral Retrotorsion Than Pitchers Without GIRD

Abstract

Background:

Dominant shoulder glenohumeral internal rotation deficit (GIRD) has been associated with pitching arm injuries. The relationship of humeral torsion on development of GIRD is not clear.

Hypothesis:

Pitchers displaying GIRD will display greater humeral retrotorsion when compared with those without GIRD.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

Humeral torsion and shoulder range of motion (ROM) were measured in 222 professional pitchers before spring training from 2009 to 2012. Shoulder external rotation (ER) and internal rotation (IR) ROM were assessed in 90° of abduction with the scapula stabilized. Humeral torsion was measured via ultrasound using previously described and validated methods. Side-to-side differences in total arc of motion (ER + IR), ER, and IR ROM and humeral torsion were calculated as nondominant minus dominant arm measures for analysis. Pitchers were classified as having GIRD if their dominant arm displayed an IR deficit ≥15° concomitant with a total arc of motion deficit ≥10° compared with their nondominant arm. A mixed-model analysis of variance (side × GIRD) was used to compare dominant and nondominant humeral torsion between pitchers with GIRD (n = 60) and those without GIRD (n = 162). Independent t tests were used to compare the side-to-side difference in humeral torsion between pitchers with GIRD and those without GIRD (α = 0.05).

Results:

Pitchers with GIRD displayed significantly less humeral torsion (ie, greater retrotorsion) in their dominant arm as compared with those without GIRD (GIRD = 4.5° ± 11.8°, no GIRD = 10.4° ± 11.7°; P = .002). Pitchers with GIRD also displayed a greater side-to-side difference in humeral torsion (GIRD = 19.5° ± 11.9°, no GIRD = 12.3° ± 12.4°; P = .001). However, pitchers with GIRD did not display an increase in dominant ER ROM (dominant ER = 131.8° ± 14.3°, nondominant ER 126.6° ± 13.1°) when compared with those without GIRD (dominant ER = 132.0° ± 14.2°, nondominant ER 122.6° ± 13.1°; P = .03). Pitchers with GIRD displayed expected alterations in ROM (IR = 28.8° ± 9.6°, total arc = 160.6° ± 15.4°; P < .01 for both) when compared with those without GIRD (IR = 39.9° ± 9.9°, total arc = 171.2° ± 15.5°).

Conclusion:

Pitchers with GIRD displayed greater side-to-side differences and dominant humeral retrotorsion as compared with those without GIRD. The greater humeral retrotorsion may place greater stress on the posterior shoulder resulting in ROM deficits. Pitchers with greater humeral retrotorsion appear to be more susceptible to developing ROM deficits associated with injury and may need increased monitoring and customized treatment programs to mitigate their increased injury risk.

Keywords

glenohumeral internal rotation deficit (GIRD)range of motion (ROM)baseball

Baseball pitching generates large forces in the throwing shoulder. The repetitive exposure to these forces affects bone and soft tissues, inducing changes in glenohumeral range of motion (ROM).^1,21 These alterations include increased humeral retrotorsion concurrent with increased external rotation (ER) and decreased internal rotation (IR) in the throwing shoulder.^{5,7,8,20,23,25,27,29} Excessive deficits in dominant shoulder IR ROM is commonly referred to as glenohumeral internal rotation deficit (GIRD) and has been associated with shoulder injury.^21,34 In these studies, injured players were defined as those having shoulder pain causing them to be unable to play or to have limited ability to play. Deficits in total arc of motion (IR + ER) as little as 5° have been shown to increase injury risk concurrent with IR deficits of 13°.³⁴ Based on these studies, GIRD that increases injury risk is best defined as concurrent deficits of IR deficit ≥15° and total arc of motion ≥10°.

Glenohumeral internal rotation deficit is attributed to increases in humeral retrotorsion, posteroinferior capsular contracture, and posterior rotator cuff tightness.⁴ While studies examining the effect of posterior-inferior capsular contracture on shoulder ROM are inconclusive,^{3,6,10,12,14,15,28} increases in humeral retrotorsion have been consistently shown to affect IR greater than ER ROM in the dominant shoulder in throwers.^{22-24,26,30-33,37} Additionally, some shift in the total arc of motion is expected, but the underlying dilemma is to what degree does humeral torsion affect excessive, potentially pathologic deficits in IR ROM.¹⁹

It has been reported that pitchers with GIRD displayed 7° greater dominant humeral retrotorsion than the nondominant arm when compared with pitchers without GIRD.³⁰ However, this study was small, with only 8 of 33 pitchers displaying GIRD over 2 seasons. Nonetheless, this finding suggests that it is difficult to interpret IR deficits in the face of altered humeral retrotorsion. Thus, further study is warranted to better elucidate the relationship between humeral torsion and alterations in shoulder ROM. The purpose of this study, therefore, was to examine the influence of humeral torsion on shoulder ROM in professional pitchers displaying GIRD. Our hypothesis was that pitchers with GIRD would have more humeral retrotorsion than those without GIRD.

Methods

Study Population

This study was conducted over 4 professional baseball seasons (2009-2012), and all players were recruited from the Colorado Rockies Major League Baseball organization. Humeral retrotorsion and clinical shoulder ROM measurements were prospectively examined in 222 individual pitchers before spring training. Subjects were excluded from the study if (1) they were being treated for a shoulder or elbow injury at the beginning of the season or (2) they were unable to participate on the first day of practice because of upper extremity injury. The Greenville Health System Institutional Review Board approved the study. All athletes signed an informed consent before beginning the study.

Data Collection

Study Questionnaire

The subjects completed a questionnaire documenting participation history, injury, and hand dominance. Examiners were blinded to hand dominance throughout the study, and side testing was randomized for each pitcher by alternating the side tested first for each pitcher. Although the examiners did not know the dominant arm, it is possible in some instances that it could be detected owing to hypertrophy of the muscles in the throwing arm. All measurements were collected on the same day during a given spring training preseason physical, and pitchers had limited bullpen sides (<30 pitches) within 72 hours of measurement. The examiners for all athletes tested were 2 experienced physical therapists.

Humeral Torsion

Humeral torsion was assessed using indirect ultrasonographic techniques as described and validated by Myers et al.²² The subjects were positioned supine on a standard treatment table with their shoulders placed in 90° of abduction and the elbow flexed to 90°. A 5-MHz transducer (Sonosite Inc) was placed level (verified with a bubble level) on the participant’s anterior shoulder and aligned perpendicular to the long axis of the humerus in the frontal plane (Figure 1). The humerus was then rotated so that the bicipital groove could be visualized with the apexes of greater and lesser tubercles parallel to the horizontal plane (Figure 2). The digital inclinometer was then placed on the ulnar side of the forearm, pressing firmly against the ulna, and it recorded the forearm inclination angle with respect to the horizontal plane, thus representing the epicondylar axis and humeral torsion.

Figure 1.

The apexes of greater and lesser tuberosities were parallel, and the angle of the ulna relative to the horizontal plane was measured as the degree of humeral torsion.

Figure 2.

Greater humeral retrotorsion was measured as a smaller angle relative to the horizontal plane.

Shoulder External and Internal Rotation ROM

A digital inclinometer was used to assess supine ER and IR ROM with the scapula stabilized at 90° of abduction. Shoulder ER and IR ROM at 90° of abduction were measured (Figure 3) for both the dominant and nondominant upper extremities with the subject positioned supine and with application of posterior force through the coracoid process to stabilize the scapula before the arm was rotated.^9,16-18 The humerus was positioned at end ROM with the force of gravity acting on the arm. No overpressure was exerted.¹⁶ Two examiners performed all measurements, with 1 examiner providing stabilization force to maintain the shoulder position while the other examiner obtained the ROM measurement.² The mean of 2 trials for both passive ROM measurements was documented.

Figure 3.

Measurement of shoulder internal range of motion.

Intrarater reliability for all humeral torsion and ROM measures was reported for all subjects within each spring, and interrater reliability was reported for 25 subjects between 2 different years. Intraclass correlation coefficients (ICCs) for intra- and interrater measures, respectively, were in the acceptable range for humeral torsion (ICC_2,1 = 0.96, SEM = 2.0°; ICC_2,k = 0.88, SEM = 3.8°), shoulder ER (ICC_2,1 = 0.94, SEM = 3.0°; ICC_2,k = 0.89, SEM = 5.8°), and shoulder IR (ICC_2,1 = 0.97, SEM = 2.2°; ICC_2,k = 0.90, SEM = 3.6°).

Variables for Data Analysis

The average of 2 trials was used for analysis for humeral torsion, ER, and IR. Total arc of rotation was calculated by adding ER and IR. Total arc deficit was calculated by subtracting the dominant from the nondominant total arc of rotation value, and GIRD was defined as the loss of internal rotation >15° with a concomitant loss of 10° total arc of motion.³⁰

Statistical Analysis

Descriptive statistics, including means and standard deviations, were used to characterize the sample and summarize ROM variables. Separate mixed-model analyses of variance (side × GIRD) were used to compare dominant and nondominant humeral torsion, IR, ER, and total arc of rotation between pitchers with GIRD and those without GIRD. Tukey post hoc tests were used to account for multiple pairwise comparisons for significant interaction effects. A secondary correlational analysis was performed to assess the relationship of humeral torsion with IR and ER ROM using Pearson correlation coefficients. Statistical significance was set a priori at α = 0.05.

Results

Pitchers with (n = 60) and without (n = 162) GIRD were not different in terms of age, height, weight, level of professional play (A league, AA league, etc), or arm dominance (P > .05) (Table 1). Overall, pitchers displayed the typical shift in total arc of motion, with an increase in ER and a decrease in IR on the dominant shoulder, consistent with previously published reports.^1,7,9 Additionally, the entire cohort displayed more humeral retrotorsion in the dominant shoulder as compared with the nondominant shoulder (Table 2).

Table 1

Subject Demographics^a

Variable	Pitchers With GIRD (n = 60)	Pitchers Without GIRD (n = 162)	P Value
Age, y	23.6 ± 2.4	24.0 ± 1.9	.91
Height, cm	191.2 ± 6.3	189.8 ± 6.5	.81
Weight, kg	95.5 ± 2.9	95.6 ± 2.3
Arm dominance (right; left), n	43; 17	126; 26	.97
Level of competition (AAA or AA; A or rookie), n	12; 48	32; 130

Values are reported as mean ± SD unless otherwise indicated. GIRD, glenohumeral internal rotation deficit.

Table 2

Humeral Torsion and ROM in Pitchers With and Without GIRD^a

Variable	Pitchers With GIRD	Pitchers Without GIRD	GIRD – No GIRD	P Value
Humeral torsion, deg
Dominant shoulder	4.5 ± 11.8	10.4 ± 11.7	−5.9^b	<.01
Nondominant shoulder	24.0 ± 10.9	22.7 ± 11.7	+1.3
Absolute S-S difference	19.5	12.3
External rotation, deg
Dominant shoulder	131.8 ± 14.3	132.0 ± 14.2	−0.1	.03
Nondominant shoulder	126.6 ± 13.1	122.6 ± 13.1	−4.0^b
Absolute S-S difference	5.2	8.7
Internal rotation, deg
Dominant shoulder	28.8 ± 9.6	39.9 ± 9.9	+11.1^b	<.01
Nondominant shoulder	54.3 ± 10.0	47.7 ± 6.7	−6.6^b
Absolute S-S difference	25.5	7.8
Total arc of rotation, deg
Dominant shoulder	160.6 ± 15.4	171.2 ± 15.5	−10.6^b	<.01
Nondominant shoulder	180.9 ± 14.6	170.3 ± 13.4	+1.5
Absolute S-S difference	20.3	0.9

Values are reported as mean ± SD. Pitchers with GIRD displayed greater humeral retrotorsion (smaller number) concurrent with their decrease in internal rotation but did not display an increase in external rotation range of motion (ROM), resulting in a deficit in total arc of motion. GIRD, glenohumeral internal rotation deficit; S-S, side to side.

Tukey post hoc comparisons revealed significant differences when the GIRD and non-GIRD shoulders were compared.

There was a significant side × GIRD interaction (F_2,220 = 12.6; P < .001) and post hoc analysis revealed that the GIRD group displayed more humeral retrotorsion on the dominant shoulder (5.9°) but no differences between groups for the nondominant shoulder (Figure 4). There was also a significant side × GIRD interaction for ER (F_2,220 = 5.0; P = .03). Post hoc analysis showed that pitchers with GIRD did not display a significant increase in ER (5.2°) as compared with their nondominant side, whereas pitchers without GIRD did display a significant increase in ER (8.7°) (Table 2). This was surprising given that increased humeral retrotorsion is thought to result in increased ER, thus suggesting that pitchers with GIRD actually had concurrent deficits of expected ER with the prevailing IR deficits. There was also a significant side-to-side deficit in IR and total arc of rotation between groups consistent with our definition of GIRD (P < .001).

Figure 4.

Pitchers who displayed glenohumeral internal rotation deficit (GIRD) displayed less dominant humeral torsion (greater retrotorsion).

There was a moderate positive association between IR ROM and humeral retrotorsion for the entire cohort and separately for pitchers with and without GIRD (r = 0.42-0.48; P < .05), indicating that as pitchers displayed more humeral retrotorsion, they tended to concurrently display less IR ROM (Figure 5). In contrast, there was not an association with ER ROM and humeral retrotorsion for the entire cohort or for each group (r = 0.06-0.19; P > .05).

Figure 5.

Glenohumeral internal rotation was moderately associated (r = 0.48) with humeral torsion, while external rotation ROM was not associated with humeral torsion.

Discussion

Our results show that pitchers who display deficits in total arc of motion and IR display greater dominant humeral retrotorsion. To our knowledge, this is the first study to show the influence of humeral retrotorsion in a large cohort of pitchers with GIRD. Humeral torsion appears to be more important than previously suggested in the interpretation of shoulder ROM deficits associated with increased injury risk. Our results show that pitchers with GIRD who displayed increased dominant humeral retrotorsion and decreased IR ROM did not display the expected concurrent gains in ER ROM. The pitchers with GIRD do not display a symmetrical total arc of motion owing to unequal changes in IR and ER motion. This suggests that those pitchers with greater humeral retrotorsion appear to undergo greater soft tissue changes affecting the magnitude of IR ROM more than those without GIRD. The observed deficits in ER suggest multiple impairments that should be considered in normalizing the total arc of motion in the throwing shoulder of pitchers with GIRD.

Our results are consistent with previous studies showing increased humeral retrotorsion in the dominant pitching shoulder as compared with the nondominant shoulder.^13,23,26 Specifically, pitchers with GIRD had a side-to-side difference of 19.5° in humeral retrotorsion when compared with the nondominant shoulder, while those without GIRD had a 12.3° side-to-side difference in humeral torsion. Additionally, the pitchers with GIRD had 5.9° more dominant retrotorsion then those pitchers without GIRD (P < .01). We think that this is an important finding, given that the large sample size confirms previous reports showing that those with GIRD displayed a similar amount of greater humeral retrotorsion (7°).³⁰

These results imply that the associated osseous adaptation with throwing may have a much more important effect on the development of GIRD than previously reported.^13,26 The prevailing thought is that the stresses placed on the posterior shoulder induce changes in the ligaments and muscles that limit internal rotation and are responsible for the development of GIRD. While this indeed may be true, our findings combined with prior results suggest that increased humeral retrotorsion is an independent risk factor for the development of GIRD.³⁰ We speculate that increased humeral retrotorsion limits the available arc of internal rotation in the follow-through phase of throwing. As such, the deceleration phase is compressed, increasing the eccentric overload to the posterior rotator cuff and in turn resulting in greater soft tissue changes and subsequent IR ROM deficits. Our results show that the pitchers in this study with GIRD not only had an IR ROM deficit, which decreased the total arc of motion, but also displayed concurrent deficits in ER ROM. This is unexpected and is in contrast to the “total arc of motion” concept that would result in an expected shift in total arc of motion toward dominant-arm ER.^2,34,36 The secondary correlational analyses show that humeral torsion is moderately associated with IR but not ER ROM regardless of group. Thus, the apparent osseous adaptation of the humerus influences clinical IR and ER ROM differently and should be considered when evaluating pitchers with GIRD.

Clinical interpretation of the influence of humeral retrotorsion in the throwing shoulder ROM is a challenging concept. In addition to the “total motion concept,” “adjusted internal rotation”^13,23,26 has been suggested as a means of interpreting losses of IR in light of side-to-side humeral torsional differences. The proposed ROM adjustment suggests that a true loss of IR would exist only when that difference exceeded the change in humeral retrotorsion. However, given our results, the GIRD group in this study had a deficit in IR of 25.5° concurrent with a humeral torsion difference of 19.5°. Yet, the non-GIRD group had a deficit in IR of 7.8° and a humeral torsion difference of 12.3°. Applying the “adjusted ROM” concept to pitchers with GIRD would demonstrate an adjusted ROM (25.5°-19.5°) of 6° IR loss, and our non-GIRD group would have an adjusted ROM (7.8°-12.3°) of an IR excess of 4.5°. The challenge with this concept is that the effect on humeral torsion across all players is not a 1:1 relationship, as demonstrated by the moderate correlations between humeral torsion and IR ROM and the lack of a relationship with ER ROM. Therefore, in our opinion, making absolute adjustments to IR and ER is not accurate and thus may not lead to meaningful identification of those at risk for injury.

In our sample of professional pitchers without GIRD, the ROM differences closely paralleled the differences in humeral retrotorsion. In that group, the dominant shoulder showed a reduction of 7.8° of dominant IR and an increase of ER of 8.7° with an increase in retrotorsion of 12.3°. The net effect was a 1° gain in total arc of motion in the dominant shoulder. Thus, in the non-GIRD group, ROM changes very closely followed changes in humeral torsion between the throwing and nonthrowing arms, thereby agreeing with the “adjusted ROM” concept.

However, in the GIRD group, the findings were quite different. This group showed an increase in humeral torsion of 19.5° in the dominant arm. There was a minimal nonsignificant increase in ER (5.2°) coupled with an IR deficit (25.5°) with an approximate 20.3° loss in total arc of motion. Interestingly, it is the gain in dominant ER that is much less than what would be expected based on the “total arc of motion” concept or given the difference in humeral torsion and so could be viewed as a deficit in “adjusted ER.” As displayed in Table 2, our GIRD group did not demonstrate greater dominant ER. In contrast, in the non-GIRD group, there was greater dominant ER observed when compared with the nondominant shoulders (8.7°).

Given previous reports showing an increased injury risk with loss of total arc of motion,^34,35 it appears that pitchers with GIRD could consider not only typical IR stretching but also a careful ER stretching program to normalize the total arc of motion. The lack of relationship between humeral retrotorsion and ER ROM observed in this study may suggest that other extra-articular influences on ER ROM should be considered to increase ER ROM, such as pectoralis major and latissimus dorsi. This is supported by recent evidence showing that deficits in flexion ROM in addition to deficits of total arc of motion increase arm injury risk in professional pitchers.³⁵ In consideration of increasing ER, the question of how much ER is desirable or even functional should also be considered. The GIRD and non-GIRD groups showed virtually identical levels of ER. While there are reports that greater ER is associated with increased velocity,¹¹ it is possible that excessive ER does not aid performance, and there may not be a need to try to increase the ER in the GIRD group. In addition, it is not clear that doing so would provide any benefit from an injury standpoint.

The real problem, therefore, in the GIRD group may lie in the fact that the increased humeral retrotorsion may make it impossible for these players to reach the necessary amount of IR needed for safe deceleration of the throwing arm. Whereas some have speculated that greater humeral retrotorsion is advantageous in preventing injury, perhaps there is a safe zone for that change, and perhaps too much retrotorsion can be detrimental.^7,13,23 Recent reports have suggested that increased humeral retrotorsion was associated with elbow injuries in collegiate pitchers.²⁴ As these changes are thought to occur during adolescence, too much throwing by the young arm may induce bony changes that are harmful in the long term. Clearly, further work on this topic needs to be done, especially regarding the relationship between humeral retrotorsion and injury in the throwing arm.

Clinically, our results in context of other evidence suggest that the degree of humeral retrotorsion should be considered when the throwing shoulder is examined. This appears to be even more important in those with GIRD (deficits >10° of total arc motion and >15° of IR). If humeral retrotorsion measures are not feasible for all throwers, we recommend that at least those who continue to have GIRD after interventions such as stretching or manual therapy be measured. Although we acknowledge that this study’s results do not directly result in this recommendation, understanding the humeral retrotorsion may assist the clinician in appropriately increasing the total arc of motion in the direction (ER vs IR) consistent with the degree of humeral retrotorsion.

The strengths of this study include the size of our study and heterogeneity of our sample. Our group comprises the largest group studied with regard to humeral retrotorsion. In addition, all of our subjects are professional pitchers, whereas many of the other referenced studies had a mix of athletic levels included. Our study is limited by the cross-sectional nature given that ROM measurements have been shown to vary depending on workload and the time when a pitcher last threw. However, given that all measures were collected on the same day during a given spring training and limited bullpen sides, this should not have affected our results.

In summary, pitchers with GIRD showed greater humeral retrotorsion as compared with those without GIRD. Interestingly, those with GIRD also displayed a deficit in expected dominant ER and total arc of motion. The clinical implications of these findings need to be further elucidated.

Footnotes

Acknowledgements

The authors acknowledge the contribution and cooperation of the Colorado Rockies Major League Baseball club; the director of medical operations, Thomas Probst, ATC, PT; and the athletic training staff for their assistance in this research project.

Presented as a poster at the 39th annual meeting of the AOSSM, Chicago, Illinois, July 2013.

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.

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