The Effect of Biceps Tension on the Glenoid Labrum in Shoulders Having Rotator Cuff Tears

Mechanical tests were performed using six shoulders obtained from fresh-frozen cadavers (avg. age=51.7 years, range=47-55) having no evidence of shoulder pathology. Specimens were dissected free of all soft tissue, except for the labrum-LHB complex and articular cartilages. The humerus was positioned in 30 ̊ of abduction in the scapular plane with 0 ̊ humeral rotation. A compressive force of 50N in the medial direction was applied to seat the humeral head in the glenoid cavity [3]. Next, a tension load of either 0N or 22N was applied to the LHB tendon. A 22N load was chosen because this magnitude was shown to affect glenohumeral range of motion and kinematics [4]. Finally, the humerus was translated relative to the glenoid by 5mm in the superior direction at a rate of 1mm/sec. This amount of displacement encompasses the range of humeral head translations encountered in patients with rotator cuff disease (excluding massive tears) [5]. Paired beads were affixed to the superior labrum and the glenoid surface, according to the six angular positions (Fig. 1, inset), but the beads on both AB and PB had the same reference bead. Serial radiographs captured the position of the beads to determine the displacement of the superior labrum.