Management of Posterior Glenohumeral Instability With Large Humeral Head Defects

Traumatic posterior instability may occasionally cause a large osteochondral lesion when the anterior humeral head is compressed against the posterior glenoid rim. This is termed a reverse Hill–Sachs lesion. Such osteochondral defects may be very large in the case of chronic locked dislocations. Even in acute posterior disclocations, closed reduction may be difficult when the humeral head is locked posteriorly over the glenoid. In such cases closed or open reduction under general anesthesia with muscle relaxation may be necessary. In cases where the anterior humeral head defect is large, reconstruction may be necessary to maintain stability. Management must be tailored to the individual patient and depends on several factors, which include the size of the defect, the duration of the dislocation, the quality of the bone, the status of the articular cartilage, and the patient’s overall health. Treatment options include skillful neglect, subscapularis-lesser tuberosity transfer into the humeral head defect, disimpaction and bone grafting, allograft reconstruction of the humeral articular surface, and arthroplasty. HISTORICAL PERSPECTIVE Posterior shoulder instability is a poorly understood clinical problem and includes a spectrum of disorders. This continuum of excessive posterior translation of the glenohumeral joint ranges from the more frequent recurrent posterior subluxation to the uncommon locked posterior dislocation. Posterior instability involving a large anteromedial humeral head impression defect, frequently called a reverse Hill–Sachs defect or a McLauglin impression lesion, is traumatic in etiology and typically includes chronic locked dislocations. The infrequent occurrence of a large anteromedial humeral head defect presents a significant technical challenge in the management of posterior shoulder instability. Many classification schemes for posterior instability have been proposed which further confound treatment decision-making. There are 3 types of posterior instability. They include: acute posterior dislocation, chronic locked dislocation, and recurrent posterior subluxation or dislocation. In the literature the distinction between an acute and chronic dislocation ranges from as little as 24 hours to as late as 6 months. As Rowe and Zarins proposed in 1982, we also define chronic dislocation as an unrecognized posterior dislocation more than 3 weeks old. Success with closed reduction beyond this period dramatically decreases, and risk of iatrogenic proximal humerus fracture is significant. While recurrent posterior subluxation is more common, traumatic acute and chronic dislocations are associated with significant anteromedial humeral head impression defects. The majority of posterior dislocations are not associated with sizeable humeral head lesions. This is especially true for dislocations that spontaneously reduce or in acutely re-