Overview of Evaluation and Management of the Unstable Shoulder With and Without Bone Loss: Definition, Measurement, and Guidelines on Treatment

Abstract

Bony lesions of the glenoid and the humeral head are very common in patients with anterior shoulder instability. Approximately 80% of them have both of these lesions at the same time, which is called a bipolar lesion. Bony lesions can be visualized by special X-ray views, CT, 3D-CT, or MRI. Among these imaging modalities, 3D-CT is the most reliable method with the contralateral shoulder as a reference. A glenoid defect ≥25% of the glenoid width causes instability even after the Bankart repair, whereas a defect ≤17.5% causes no instability. The zone between 17.5 and 25% is a gray zone, called a subcritical bone loss. A Hill-Sachs lesion does not have a critical size by itself because its risk of causing instability depends not only on the Hill-Sachs lesion but also on the size of the glenoid. In order to assess these lesions together, the glenoid track concept has been introduced. If a Hill-Sachs lesion is on the glenoid track (on-track lesion), there is no risk of instability. If a Hill-Sachs lesion is extending medially over the glenoid track (off-track lesion), there is a risk of instability. Treatment options can be determined using the glenoid track concept, and its clinical efficacy has been validated. Indication, surgical technique, and clinical outcome of bony fragment fixation need to be determined.