Imaging of shoulder instability.

The glenohumeral joint is an inherently unstable articulation and consequently the most frequently subluxed and frankly dislocated joint in the body. Shoulder instability can be uni- or multidirectional related to acute or repetitive stress and is occasionally secondary to congenital or developmental abnormalities such as a lax joint capsule or glenoid dysplasia. The clinical diagnosis of instability can be difficult, and knowledge of the imaging findings of anterior, posterior, multidirectional, and microinstability is essential to guide the correct treatment of these patients. This requires the appropriate use of many different imaging modalities as well as specific positioning and directed protocols. This review article explains the clinical scenarios associated with shoulder instability and how they relate to the choice of imaging techniques. The imaging findings of the most common soft tissue and osseous pathology are reviewed and explained with specific attention to anterior and posterior instability.