Neoinnervation in rotator cuff tendinopathy.

The aim of this study was to determine whether there are more nerves in tendinopathic human tendon, and if so, where are they located. Tendon biopsies were collected from normal, tendinopathic, and torn human rotator cuff tendons and then analyzed using immunohistochemistry and antibodies against a general nerve marker (protein gene product 9.5, PGP9.5), a nerve regeneration marker (growth-associated protein 43, GAP43), and an endothelial cell marker (CD34). Nerve fibers exhibiting PGP9.5 or GAP43 immunoreactivity were often observed intimately in association with tiny blood vessels in the endotendineum of tendinopathic tendons. The expression of PGP9.5 and GAP43 were significantly higher in tendinopathic tendon compared with control tendon and torn tendon. These data support the hypothesis that early tendinopathy is associated with increases of newly grown nerve fibers and blood vessels inside and around tendinopathic tendon, and these may be the source of pain in tendinopathy.