It is important to understand the precise structure of the soft tissue around the superior glenoid in order to consider the etiology of SLAP (superior labrum anterior and posterior) lesions. The purpose of this study was to histoanatomically investigate the fibers of the superior labrum. Forty-nine embalmed shoulder joints of cadavers were used. After the shoulder girdle was cut off, posterior rotator cuff muscles were detached from the capsule. The posterior capsule was resected taking care not to injure the glenoid and anterior soft tissue. After recording macroscopic findings by a digital camera, Hematoxylin-Eosin stain was performed in 11 shoulders. Furthermore, Elastica van Gieson was stained in selected specimens. In the posterior part, the long head of the biceps tendon (LHB) fibers intermingled with the superior labrum. LHB fibers were kept from connecting to the anterosuperior labrum by the sheet-like structure branching off the rotator interval tissue. This sheet-like structure was abundant in elastic fibers, which were not found much in other parts of the superior labrum, and different from the superior glenohumeral ligament. The results suggest that most of the LHB fibers exist in the posterior portion of the glenoid which resist the traction force from the biceps brachii muscle. This is quite reasonable considering that the bicipital groove is usually located more anteriorly than the LHB origin. As the sheet-like structure histologically connects the rotator interval tissue and anterosuperior labrum, the anterosuperior labrum could work as a part of the flexible support system of the humeral head which tends to move slightly anteriorly.
