Reduction of sensory responses to passive movements of inflamed knee joints by hylan, a hyaluronan derivative.

Hyaluronan (sodium hyaluronate) is a glycosaminoglycan that is present in all joint tissues. Painful arthritic joints have been characterized by hyaluronan of reduced elastoviscosity. The purpose of this investigation was to determine whether hyaluronan has an influence on joint nociceptor sensitivity and whether restoration of elastoviscosity would decrease nerve responses from nociceptive afferent fibers in arthritic joints. Nerve impulse activity was recorded from nociceptive afferent fibers of the medial articular nerve in anesthetized cats. An acute experimental arthritis was produced by intra-articular injection of kaolin and carrageenan. This caused, within 3 h, the development of ongoing nerve activity and enhancement of nerve impulse responses to passive movements in the normal range of the joint. Intra-articular injection of an elastoviscous solution of hylan, a hyaluronan derivative, significantly reduced both the ongoing activity and the movement-evoked responses in 1-2 h. This effect was not obtained when a nonelastoviscous solution of hylan was injected into the inflamed joint. The results indicate that intra-articularly injected elastoviscous solutions of hylan reduced nociceptive activity in inflamed joints through an elastoviscous, rheological effect on nociceptive afferent fibers through the intercellular matrix in which these fibers are embedded.