The pattern of the collagen fiber bundles of the capsule of the glenohumeral joint.

The macroscopic anatomy and the architecture of the collagen fiber bundles were studied in the joint capsules of 43 cadaver shoulders. All the specimens were transilluminoted by polarized light after preparation by Spalteholz' technique. Areas of high-fiber density and complex structure were examined histologically. The macroscopically recognizable ligaments are composed of collagen fiber bundles in several layers of differing thickness and orientation. A simple pattern of radial and circular fibers is found only in the relatively thin posterior capsule. A complex pattern of cross-linking was visible in the superior capsule, and a system of fiber bundles spirally crossing each other was present in the anterior/inferior capsule. The examination under polarized light revealed a continuous transition between the ligamentous reinforcements at the anterior inferior capsule, which radiated obliquely from the glenoid rim and varied greatly in form and orientation. The complicated structure of the joint capsule would suggest that the capsular cylinder has to be regarded as a functional entity and that the current biomechanical concepts must be modified if we want to understand its stabilizing effect. The structural features of the superior capsule present new insight about the pathogenesis of rotator cuff tearing, which can develop as a result of shearing stress between the capsular and tendinous layers.