Internal impingement in the shoulder.

Current wisdom holds that the acromion is a major factor in the development of rotator cuff impingement. From the examination of a large number of skeletal specimens (1232 shoulders), we conclude that this view may require some modification. It appears that internal impingement between the glenoid and the humeral head may also be a significant mechanism in the development of rotator cuff pathosis. We present here the evidence for this internal impingement, which is expressed in characteristic telltale patterns impressed into the bones on both sides of the joint. If this thesis is correct, the rationale for some acromioplasty operations may be called into question, currently the most popular procedure in shoulder surgery.