Shoulder: Instability

Abstract

The glenohumeral joint is vulnerable to injury and instability due to its extreme mobility and range of motion. The inherent lack of osseous constraint requires dynamic stabilization by the rotator cuff and other muscles. Joint stability also depends heavily on static structures providing passive constraint. The glenoid labrum and glenohumeral ligaments are the most important static restraints and nearly always demonstrate characteristic abnormalities on magnetic resonance (MR) images in unstable shoulders. The clinical spectrum of instability ranges from obvious recurrent dislocations to equivocal, inconclusive symptoms that may mimic other shoulder disorders, such as rotator cuff tear and biceps tendon dislocation. When instability is obvious, imaging studies are useful for lesion characterization and preoperative planning. When clinical symptoms are inconclusive, the emphasis shifts to diagnostic interpretation for choice of treatment options.