Shoulder: Instability

Abstract

Glenohumeral instability is the inability to keep the humeral head centered in the glenoid fossa. Glenohumeral instability can be classified according to etiology and direction of instability. The glenoid labrum, the glenohumeral ligaments, and the bony structures contribute to the stability glenohumeral joint and need to be addressed with imaging. One of the difficulties with accurately diagnosing labral tears on MR imaging is the normal labral variants, which can sometimes appear similar to tears. The location and extent of a Hill-Sachs lesion and glenoid rim defects need to be related to recognize engaging Hill-Sachs lesions or off-track situations. There are several types of labral tears that are not associated with a prior dislocation. SLAP tears are one of the more common tears of the labrum and can sometimes be difficult to distinguish from a normal variant superior sublabral recess. Labral tears in overhead thrower occur in the posterosuperior labrum, adjacent to the posterior rotator cuff tears in these athletes. Tears in the posterosuperior labrum are also associated with spinoglenoid notch paralabral cysts, which can be painful and cause external rotation weakness.