Disabled Throwing Shoulder 2021 Update: Part 1-Anatomy and Mechanics

The purpose of this article is to provide updated information for sports health care specialists regarding the Disabled Throwing Shoulder (DTS). A panel of experts, recognized for their experience and expertise in this field, was assembled to address and provide updated information on several topics that have been identified as key areas in creating the DTS spectrum. Each panel member submitted a concise presentation on one of the topics within these areas, each of which were then edited and sent back to the group for their comments and consensus agreement in each area. Part 1 presents the following consensus conclusions and summary findings regarding anatomy and mechanics, including: 1) The current understanding of the DTS identifies internal impingement, resulting from a combination of causative factors, as the final common pathway for the great majority of the labral pathoanatomy; 2) intact labral anatomy is pivotal for glenohumeral stability, but its structure does not control or adapt well to shear or translational loads; 3) the biceps plays an active role in dynamic glenohumeral stability by potentiating "concavity compression" of the glenohumeral joint; 4) the ultimate function of the kinetic chain is to optimize the launch window, the precise biomechanical time, and position for ball release to most effectively allow the ball to be thrown with maximum speed and accuracy, and kinetic chain function is most efficient when stride length is optimized; 5) overhead throwing athletes demonstrate adaptive bony, capsular, and muscular changes in the shoulder with repetitive throwing, and precise measurement of shoulder range of motion in internal rotation, external rotation, and external rotation with forearm pronation is essential to identify harmful and/or progressive deficits. LEVEL OF EVIDENCE: Level V, expert opinion.