Internal impingement of the shoulder.

Internal impingement has been proposed as a cause of dead arm syndrome. Recent information, however, suggests that internal impingement is not pathologic; it is a natural restraint to hyperexternal rotation. The loss of internal impingement is pathologic, allowing hyperexternal rotation with hypertwist and fatigue failure of rotator cuff fibers. The "dead arm" of the throwing athlete may be caused by superior labrum anterior and posterior lesions or by SICK scapula syndrome (scapular dyskinesis). Superior labrum anterior and posterior lesions typically require arthroscopic repair, whereas the scapular dyskinesis can generally be treated with a focused rehabilitation program. Open anterior stabilization surgery should not be used to treat dead arm syndrome.