EFFECT OF LESIONS OF THE SUPERIOR PORTION OF THE GLENOID LABRUM ON GLENOHUMERAL TRANSLATION

Lesions of the superior portion of the glenoid labrum were created in seven cadaveric shoulders. The shoulders were mounted on a special app aratus attached to a servocontrolled hydraulic materials-testing devic e. Sequential fifty-newton anterior, posterior, superior, and inferior forces and a twenty-two-newton joint compressive load were applied to the shoulders. In addition, a fifty-five-newton force was applied to the tendon of the long head of the biceps brachii. The shoulders were tested in seven positions of glenohumeral elevation and rotation. An i solated lesion of the anterosuperior portion of the labrum, which did not involve the supraglenoid insertion of the biceps brachii, had no s ignificant effect on anteroposterior or superoinferior glenohumeral tr anslation, either with or without application of the fifty-five-newton force to the biceps brachii tendon. In contrast, a complete lesion of the superior portion of the labrum that destabilized the insertion of the biceps resulted in significant increases in anteroposterior and s uperoinferior glenohnmeral translations. At 45 degrees of glenohumeral elevation, the complete lesion led to a 6.0-millimeter increase in an terior translation,when the arm was in neutral rotation and to a 6.3-m illimeter increase when the arm was in internal rotation; inferior tra nslation also increased, by 1.9 to 2.5 millimeters. The increases in t ranslation persisted despite application of a fifty-five-newton force to the long head of the biceps.