Fiber components of the shoulder superior labrum

The purpose of this study was to investigate the anatomy of the superior glenoid labrum focusing on the fiber arrangement of its components.

Forty-nine embalmed shoulder girdles were removed and each posterior capsule was incised. After recording the macroscopic findings 12 superior-half glenoids were histologically examined. In nine serially sectioned glenoids, four were cut parallel to and five were cut vertical to the glenoid surface. The remaining three glenoids were radially sectioned at the clock position for each hour between 10:00 and 14:00.

The superior labrum had a semi-circular fiber component along the outer margin of the glenoid. In addition, a so-called 'sheet-like structure' which branched off the rotator interval and contained many elastic fibers, attached to its anterosuperior portion. The fibers of the sheet-like structure mixes with fibers of the semi-circular component and ran posteriorward. The fibers of the long head of the biceps tendon extended posteriorward from its origin along the glenoid edge. These fibers communicated with other labrum fibers and became a major element of the posterior portion.

The superior labrum is not homogenous. The posterior portion mainly consists of the robust fiber component of the long head of the biceps tendon. The anterosuperior portion includes fibers of the sheet-like structure which contains numerous elastic fibers. Tensile stress from the rotator interval might be conveyed to the anterosuperior labrum.