Impingement of the deep surface of the supraspinatus tendon on the posterosuperior glenoid rim: An arthroscopic study.

Seventeen athletes presenting with unexplained shoulder pain on throwing underwent arthroscopic examination. All but one practiced a throwing sport. The dominant arm was involved in all patients except one bodybuilder. Their mean age was 25 years (range 15 to 30 years), and they had symptoms present for a mean of 27 months. None had clinical, radiologic, or arthroscopic evidence of anterior instability. Preoperative clinical examination typically revealed localized pain on full external rotation and 90° abduction, signs of rupture of the rotator cuff, and positive impingement sign. In 10 cases computed tomographic arthrogram showed evidence of abnormality at the posterior edge of the glenoid. The mean humeral retrotorsion was 10° (range 5° to 30°). Under arthroscopy, with the arm placed in full external rotation and 90° abduction (the throwing position), impingement was found between the posterosuperior border of the glenoid and the undersurface of the tendinous insertions of supraspinatus and infraspinatus. A partial rupture of the cuff, which was demonstrated by arthrogram, was confirmed in eight patients, whereas a partial capsulotendinous rupture, which was not demonstrated by arthrogram, was seen in nine patients. Twelve patients had further lesions of the posterosuperior labrum. This study suggests that in addition to Neer's "impingement syndrome" and Jobe's "instability with secondary impingement," impingement of the undersurface of the cuff on the posterosuperior glenoid labrum may be a cause of painful structural disease of the shoulder in the thrower.