A bilateral comparison of posterior capsule thickness and its correlation with glenohumeral range of motion and scapular upward rotation in collegiate baseball players

Hypothesis: We hypothesized that posterior capsule thickness (PCT) would be greater on the dominant arm compared to the non-dominant arm. We also hypothesized that PCT would negatively correlate with glenohumeral internal rotation and scapular upward rotation. In addition, PCT would positively correlate with glenohumeral external rotation. However, currently PCT has not been measured nor have correlations been identified to exist with glenohumeral and scapular motion. Therefore, the purpose of the study was to determine if the posterior capsule was hypertrophied on the dominant arm and to identify if relationships exist with glenohumeral internal rotation (IR), external rotation (ER), and scapular upward rotation (SUR). Materials and methods: PCT was measured using a 10-MHz transducer. Glenohumeral IR and ER was measured supine using a digital inclinometer. SUR was measure at 0 degrees, 60 degrees, 90 degrees, and 120 degrees of glenohumeral abduction using a modified digital inclinometer. Results: PCT was greater on the dominant compared with the nondominant arm (P = .001). A negative correlation was found between PCT and IR (-0.498, P = .0001). A positive correlation was found between PCT and ER (0.450, P = .002) and between PCT and SUR at 60 degrees, 90 degrees, and 120 degrees of glenohumeral abduction (0.388, P = .006; 0.327, P = .023; 0.304, P = .036, respectively). Discussion: This in vivo study demonstrated a hypertrophied posterior capsule and its association with GIRD, ER, and SUR. These observations suggest that PCT does occur on the throwing arm of baseball players and is linked with glenohumeral and scapular alterations. Conclusions: This methodology could be used as a noninvasive screening evaluation for overhead athletes to identify those who may be at risk for shoulder injuries due to excessive capsular thickening. Level of evidence: Basic Science Study, Anatomic Study Using Healthy Volunteers. (C) 2011 Journal of Shoulder and Elbow Surgery Board of Trustees.