Quantification of the Dynamic Glenohumeral Stability Provided by the Rotator Cuff Muscles in the Late Cocking Phase of Throwing: Seok-Beom Lee, Shawn W. O'Driscoll, Bernard F. Morrey and Kai-Nan An

During the late cocking phase of throwing, the humerus maintains its level of abduction and moves into the scapular plane while externally rotating from 460 to 1700 • In this position the head of the humerus is angled so that it can stretch the anterior structures. This creates the potential for anterior instability. Baseball pitchers with unstable shoulders demonstrated several significant differences from pitchers with normal shoulders during the late cocking phase. Jobe et ale (1983) reported that the player with unstable shoulder might begin with some compensatory mechanics, such as moving the humerus into the coronal plane. When the humerus moves into the coronal plane, the head of humerus angles even further anteriorly.