MRI in dislocation and instability of the shoulder joint

The value of magnetic resonance imaging (MRI) in shoulder instability depen ds on its ability to demonstrate pathologic lesions within the joint. Traum atic dislocation in particular often results in capsulo-labral-avulsion, st retching 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 indir ect arthrography, gadolinium is intravenously injected and enhances the art icular space. With direct arthrography, gadolinium or saline are injected i nto the joint, optimising the demonstration of labral lesions. In grade I lesions, fluid enters the lesion without deformation or detachme nt of the labrum. In grade II lesions, the labrum is of abnormal size or sh ape, but still attached to the glenoid. In grade III lesions, the labrum is completely detached. Sensitivity of magnetic resonance arthrography for la bral lesions is 90% and specificity is 95%. Impression fractures at the hum eral head are well demonstrated but avulsion fractures at the glenoid are n ot. Lesions at the joint capsule cannot be seen. Decisions relating to shoulder instability are primarily based on patient h istory and physical examination. MRI adds valuable information, particular in unclear clinical settings.