[Stability versus mobility of the shoulder. Biomechanical aspects in athletes]

The demand profile of athletes shoulders is high. On the one hand the shoulder has to provide a maximum active range of motion that allows rapid movements of the arm and on the other hand it has to be sufficiently stabilized to decelerate rapid movements and to neutralize the resulting translational forces. Two general types of instability can be differentiated in athletes shoulders: the macroinstability typically occurring in athletes involved in contact sports and the microinstability occurring in athletes involved in overhead sports.Repetitive abduction and external rotation movements of athletes involved in overhead sports lead to adaptation of the glenohumeral joint capsule and ligaments. The anterior capsule becomes stretched while the posterior capsule develops tightness. These adaptations can result in an anterior microinstability as well as posterosuperior impingement (PSI) which implicates a pathological contact of the posterosuperior rotator cuff with the posterior glenoid and which is also associated with SLAP lesions. In contrast the shoulders of swimmers are prone to anterosuperior impingement because the arm stroke involves a forceful combined anteflexion, adduction and internal rotation of the arm.The macroinstability of contact athletes is caused by sufficient trauma and characterized by a structural lesion of capsulolabral or bony lesion. While the empirical recurrence risk of young contact athletes is already high, it can be further impaired by bony defects of the glenoid. In suspected cases, critical glenoid defects should be quantified by computed tomography (CT) scans and treated by bony augmentation of the glenoid.