Mechanoreceptors in the ligaments and joint capsule of the canine shoulder joint: histological and immunohistochemical studies.

To better understand the role of ligaments and joint capsule in canine shoulder joint stability, the presence of mechanoreceptors was detected by means of a modified gold chloride stain and immunohistochemical (IHC) methods with antibodies against PGP 9.5, p75 and S100. Two morphologically distinct mechanoreceptors were identified: Ruffini corpuscles (type I endings) and Pacinian corpuscles (type II endings). These receptors are mainly localized in the medial gleno-humeral ligament, in particular in the cranial arm of the insertion into the scapula, and in the caudal part of the joint capsule. In addition, as reported by some prior histological studies on ligaments (Morisawa, J Orthop Sci 3, 1998; Guanche et al, Orthopedics 22, 1999), the gold chloride method identified also a few Golgi tendon organ-like receptors (type III endings); on the contrary, the IHC study did not confirm this datum. The variety of mechanoreceptors in canine shoulder joint might indicate an afferent function in providing the CNS with joint proprioceptive information. Therefore, besides acting as passive mechanical stabilizers, the ligaments and the joint capsule may serve as sensory structures, contributing actively to joint stability. Capsulo-ligamentous injuries which occur in shoulders not only affect mechanical restraint but also alter the proprioceptive input to the CNS by means of disruption of the mechanoreceptors.