Effects of biceps loading and arm rotation on the superior labrum in the cadaveric shoulder

Effects of loading the long head of the biceps brachii (LHB) and arm rotati on on the strain of the superior labrum (anterior and posterior) in 10 fres h frozen cadaveric shoulder joints were studied. Loads were applied to the rotator cuff muscles to stabilize the humeral head. The strain of the anter ior and posterior portions of the labrum with the biceps loaded with 0.42 k g, 1.36 kg, and 2.31 kg were measured using linear transducers. The humerus was rotated externally (30, 45, 60, and 90 degrees) and internally (30, 45 , and 60 degrees) with the arm elevated 60 degrees at glenohumeral joint (s imulated 90 degrees elevation of arm to the trunk). The strain increased wi th an increase in the weight of the load to LHB and with increase in rotati on angle both internally and externally. Since the strain in the posterior portion was larger than that of the anterior portion it seems likely that t he labrum, especially the posterior portion, is subject to large strain dur ing biceps loading and arm rotation. (C) 2000 Tohoku University Medical Pre ss.