Humeral retroversion and its association with posterior capsule thickness in collegiate baseball players

Baseball players commonly present with decreases in internal rotation (IR) and concurrent increases in external rotation (ER) motion. Several glenohumeral (GH) adaptations have been theorized to cause these changes in motion, including humeral retroversion (HR) and posterior capsule thickness (PCT). However, limited data exist examining the inter-relationship between HR and PCT. Therefore, the purpose of this study was to measure HR, GH IR and ER rotation, and PCT.

HR and PCT were measured with an ultrasound system (Sonosite Titan; Sonosite, Bothell, WA, USA), and GH IR and ER were measured with a digital inclinometer.

The dominant arm had significantly more HR (15.6°, P = .0001) than the nondominant arm. Pearson correlation coefficients showed a significant negative relationship between HR and GH IR (-0.472, P = .001) and a significant positive relationship between HR and GH ER (0.295, P = .042). A significant positive correlation was also found between HR and PCT (0.427, P = .003).

This was the first study to identify a relationship between HR and PCT in addition to GH IR and ER. The identification of these multiple correlations appears to suggest that the loss of IR caused by HR may be placing additional stress on the posterior capsule during the deceleration phase of the throw, thereby causing a fibroblastic healing response.

HR has previously been identified as a positive adaptation because of the increase in ER without anterior capsule attenuation. However, this study suggests that HR may be contributing to the negative adaptation of PCT.