Update in shoulder magnetic resonance imaging.

The shoulder is capable of the largest range motion of any articulation in the human body. Because it is inherently unstable, the glenohumeral joint is dependent on the support given by surrounding muscular, ligamentous, and tendonous structures. A variety of disorders may involve these structural supports and lead to shoulder pain and dysfunction. Refinements in magnetic resonance (MR) imaging techniques have allowed improved characterization of these abnormalities and may permit earlier and more specific diagnoses in patients with shoulder pain. Theories as to the pathogenesis of rotator cuff disease include intrinsic and extrinsic impingement as well as overload tendinosis. MR is useful in the evaluation of rotator cuff impingement and tears. The classification and MR assessment of glenohumeral instability has recently received increased attention yet remains an area of difficulty. MR arthrography has been used with some success in the evaluation of instability demonstrating improved diagnostic sensitivities and specificities when compared with conventional MR. Relatively little attention has been paid to MR evaluation of the shoulder after surgery. Micrometallic artifact, distortion of soft-tissue planes, and persistent signal abnormalities within rotator cuff and capsulolabral structures may hinder assessment of recurrent tear or instability in the postoperative patient.