[MRI in dislocation and instability of the shoulder joint]

The value of magnetic resonance imaging (MRI) in shoulder instability depends on its ability to demonstrate pathologic lesions within the joint. Traumatic dislocation in particular often results in capsulo-labral-avulsion, stretching of the joint capsule and impression fracture at the humeral head. Various MR weightings, including spin echo and gradient echo, are useful at the shoulder. A surface coil should be used. Image planes are oriented at the scapula. A capsulo-labral-avulsion can not be reliably demonstrated on non-contrast imaging in the absence of intra-articular effusion. With indirect arthrography, gadolinium is intravenously injected and enhances the articular space. With direct arthrography, gadolinium or saline are injected into the joint, optimising the demonstration of labral lesions. In grade I lesions, fluid enters the lesion without deformation or detachment of the labrum. In grade II lesions, the labrum is of abnormal size or shape, but still attached to the glenoid. In grade III lesions, the labrum is completely detached. Sensitivity of magnetic resonance arthrography for labral lesions is 90% and specificity is 95%. Impression fractures at the humeral head are well demonstrated but avulsion fractures at the glenoid are not. Lesions at the joint capsule cannot be seen. Decisions relating to shoulder instability are primarily based on patient history and physical examination. MRI adds valuable information, particular in unclear clinical settings.