Supraspinatus Outlet Impingement
Superior subluxation of the humeral head results in impingement of the supraspinatus tendon which runs between this structure and the overlying acromion. Tendon degeneration and eventual rupture occurs as seen in the example below. Here the humeral head abuts the acromion and the ruptured tendon has retracted to the level of the glenoid labrum. There is marked atrophy of the supraspinatus muscle belly. Degenerative disease is also present in the acromioclavicular (AC) joint.
Coronal and sagittal T1 weighted images are shown: