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The glenohumeral joint has a wide range of motion which can be advantageous in activities such as overhead throwing sports or occupational activities that require a wide variety of movements in the shoulder. However, this wide range of motion makes it an unstable joint and this is the major reason why shoulder instability and shoulder dislocation are very frequent in traumatic injuries such as falls and sports-related injuries. It is important to be familiar with the normal anatomical and pathologic imaging appearances of the structures in the shoulder to effectively diagnose and treat glenohumeral instability injuries. This chapter provides an up-to-date review of the normal shoulder anatomy and the various clinical and imaging features involved in glenohumeral instability with an emphasis on the MRI manifestations.

The glenohumeral joint is a classic ball and socket type joint which allows a broad range of movement but whose shallow glenoid component compromises the inherent stability of the joint. Only 25–30% of the humeral head contacts the glenoid surface [1]. The joint is fortified by both intrinsic and extrinsic components. Compromise of any of the intrinsic or extrinsic stabilizers of the joint can lead to joint laxity and result in either unidirectional or multidirectional glenohumeral instability.Imaging, specifically MRI and MR arthrography, provides a reliable means of identifying structural features contributing-to or associated with glenohumeral instability, which may be critical factors in determining optimal management of patients with instability of the glenohumeral joint.