Myxoid and globular degeneration of nerves in the shoulder joint.

Characteristic degeneration of the nerves in shoulder joints was recognized in 26 of 35 capsules (74.3%) from 20 cadavers. No left or right or gender differences were found. Histologic features of the nerves were (1) thickening of the perineurium, (2) myxoid degeneration in the endoneurium, and (3) hyaline globular structures with a whorled, oligocellular appearance regarded as Renaut bodies. The results of histochemical and electron microscopic studies showed prominent degenerated collagen fibers in the globular areas. These features resembled those found in the fusiform swelling in the axillary nerve branch to the teres minor muscle, believed to be caused by chronic nerve compression. Sixty percent of the degenerated nerves occurred in the anteroinferior and posteroinferior portions of the capsule, an area that is considered to be innervated by the axillary nerve. No correlation between age and severity of these degenerative nerve changes was noted. Compression of the axillary nerve and inferior joint capsule caused by repetitive shoulder movement such as forward flexion, abduction, and external rotation of the humerus might result in this form of nerve degeneration found histologically over a lifetime without necessarily causing clinical symptoms.