Posterior Capsule Hypertrophy’s Impact on Pitchers

What is the relationship between posterior capsule adaptations and soft tissue glenohumeral internal rotation deficit in healthy pitchers? A new study may have answers.

The study, “The Contribution of Posterior Capsule Hypertrophy to Soft Tissue Glenohumeral Internal Rotation Deficit in Healthy Pitchers,” was published online on January 12, 2022 in The American Journal of Sports Medicine.

How, these investigators wondered, is the thickness of the posterior capsule associated with soft tissue glenohumeral internal rotation deficit in healthy pitchers? They hypothesized that there would be a positive relationship in the dominant arm, but not the nondominant arm. They also believed they would find a strong positive relationship between soft tissue glenohumeral internal rotation deficit and the bilateral difference in posterior capsule thickness.

The study enrolled 45 healthy collegiate and professional pitchers. The research team measured glenohumeral internal rotation, external rotation range of motion, humeral retroversion, and posterior capsule thickness bilaterally for each participant.

They found that while posterior capsule thickness was not associated to soft tissue glenohumeral internal rotation deficit in either arm, the amount of posterior capsule hypertrophy was moderately related (p = .007). They explained that as the posterior capsule hypertrophied, soft tissue glenohumeral internal rotation deficit moderately increased.

“If posterior capsule thickness measurements are feasible, clinicians should consider performing bilateral ultrasound assessments to isolate posterior capsule adaptions [such as posterior capsule hypertrophy]. This will allow clinicians to identify pitchers with potentially maladaptive structural adaptations and optimize management strategies throughout the season to counteract them,” the researchers wrote.

Study authors included Ryan W. Paul of Rothman Orthopaedic Institute in Philadelphia, PA, Scott Sheridan of the Major Leagues Umpire Association in New York, Katherine E. Reuther of University of Pennsylvania in Philadelphia, PA, John D. Kelly, IV, M.D., also of the University of Pennsylvania, and Stephen J. Thomas of Thomas Jefferson University in Philadelphia, PA.