Background: The relationship between posterior capsule adaptations and soft tissue glenohumeral internal rotation deficit (GIRD) in healthy pitchers remains unclear.
Purpose/hypothesis: This study aimed to identify if posterior capsule thickness (PCT) was associated with soft tissue GIRD in healthy pitchers. We hypothesized that there would be a positive relationship between soft tissue GIRD and PCT in the dominant arm, no relationship between soft tissue GIRD and PCT in the nondominant arm, and a strong positive relationship between soft tissue GIRD and the bilateral difference in PCT (posterior capsule hypertrophy [PCH]).
Study design: Cross-sectional study; Level of evidence, 3.
Methods: A total of 45 healthy collegiate and professional pitchers were included. Glenohumeral internal rotation and external rotation range of motion, humeral retroversion, and PCT were measured bilaterally. PCT was determined for unilateral posterior capsule measurements, and PCH of the throwing shoulder was calculated as the bilateral difference in PCT. Soft tissue GIRD was calculated as the sum of clinical GIRD and the bilateral difference in humeral retroversion. Pearson correlation coefficients were determined to evaluate the relationships between dominant arm PCT, nondominant arm PCT, and PCH and soft tissue GIRD.
Results: Pearson correlations showed that both dominant arm PCT (R = -0.13; P = .378) and nondominant arm PCT (R = 0.21; P = .165) were not related to soft tissue GIRD. However, Pearson correlations did show that the amount of PCH was moderately related to soft tissue GIRD (R = 0.40; P = .007). Therefore, as the posterior capsule hypertrophied, soft tissue GIRD moderately increased.
Conclusion: Increased PCH was associated with an increase in soft tissue GIRD in healthy pitchers. If PCT measurements are feasible, clinicians should consider performing bilateral ultrasound assessments to isolate posterior capsule adaptations (ie, PCH). This will allow clinicians to identify pitchers with potentially maladaptive structural adaptations and optimize management strategies throughout the season to counteract them.
Keywords: GIRD; baseball; pitching; range of motion; ultrasound.