Chronic Structural Adaptations of the Shoulder and Elbow Are Correlated in Professional Baseball Pitchers

Pitchers with deficits in total shoulder rotation range of motion (ROM) are 2.6 times more likely to experience an elbow injury. Despite the effects of shoulder ROM on elbow injury, it is currently unclear whether specific tissue adaptations of the shoulder relate to the tissue adaptations of the elbow in baseball pitchers.

The purpose was to evaluate the relationship between chronic structural adaptations of the shoulder (humeral retroversion [HR], posterior capsule thickness [PCT], infraspinatus/teres minor pennation angle, and muscle thickness) and chronic structural adaptations of the elbow (ulnar collateral ligament [UCL] thickness, ulnohumeral joint laxity with valgus stress, and ulnar nerve cross-sectional area) in professional baseball pitchers. It was hypothesized that chronic adaptations of HR and PCT would relate to structural adaptations of the elbow.

Cross-sectional study; Level of evidence, 3.

Healthy minor league right-handed baseball pitchers from a single professional baseball organization were enrolled during 2022 preseason medical evaluations. Enrolled pitchers underwent bilateral shoulder ultrasound examination of HR, PCT, and posterior rotator cuff pennation angle and muscle thickness as well as bilateral elbow ultrasound examination of the ulnar nerve, UCL thickness, and ulnohumeral joint gapping using the Telos device. The difference in ulnohumeral joint gapping from stressed (150 N) to unstressed (ie, delta value) was calculated. Bilateral differences in every included measure were calculated and used for analysis to more closely isolate chronic adaptations. Multivariate stepwise regressions were performed to determine whether the chronic structural and clinical (strength and ROM) shoulder adaptations were related to structural adaptations of the elbow.

Overall, 40 right-handed professional baseball pitchers with a mean age of 22 ± 3 years were included. A significant positive relationship was observed between preseason structural adaptations of UCL thickness and PCT (R = 0.344; R² = 0.118; P = .030) as well as between chronic structural adaptations of ulnar nerve cross-sectional area and teres minor muscle thickness (R = 0.387; R² = 0.150; P = .020). No statistically significant relationships were found between chronic structural adaptations of the shoulder and delta ulnohumeral joint gapping (all P > .05) or between chronic adaptations in clinical measures (strength and ROM) of the shoulder and chronic structural adaptations of the elbow (all P > .05).

Positive relationships between chronic adaptations of UCL thickness and PCT, as well as between ulnar nerve cross-sectional area and teres minor MT, were observed in asymptomatic minor league pitchers. However, no significant relationships between adaptations in shoulder strength or ROM were related to chronic structural adaptations of the elbow.