The anatomy in shoulder instability

Abstract

The shoulder is the most mobile and least stable joint of the human body. The bony anatomy determines a very limited stability, which has to be maintained by the surrounding soft tissues that act as static stabilizers. In addition, dynamic stability is provided by the musculotendinous units of the rotator cuff and scapulothoracic joint. The clinical pattern of the instability determines the anatomical lesions that may appear. Overall, traumatic instabilities originate detachments of the labrum and pathological stretching of the capsuloligamentous complex that, in absence of healing, develop recurrent instability. On the other hand, atraumatic instabilities might course with absence of injury of the static stabilizers, and only increased capsular volume is found. Bone deficits, as on the glenoid rim or the humeral head, predispose to recurrent instability even after soft-tissue stabilization procedures, so preoperative assessment of bone loss is crucial to obtain favorable outcomes in terms of patient satisfaction and recurrence.