Increased friction of animal joints by experimental degeneration and recovery by addition of hyaluronic acid

Objective. To investigate the lubricating ability in osteoarthritic (OA) stifle joints. Design. An experimental study in rabbit stifles in vitro. Background. The lubricating ability in OA joints, and the effects of the application of hyaluronic acid (HA), a drug for OA, to the osteoarthritic joints have not yet been reported. Methods. The friction in OA stifles induced by two different methods, the intra-articular injection of papain, and transection of the anterior cruciate ligament (ACL) was measured using a robotic arm under force control. Results. The frictional coefficient in the papain-injected model, that caused slight degeneration in the articular cartilage, was 1.3 to 1.8 times as large as that in the contralateral uninjected stifles. The elevated values decreased significantly by addition of HA to the articular surface (P < 0.05). In another group (n = 4), the frictional coefficient in the stifle at 9 months after ACL transection that caused severe degeneration in the articular cartilage was 1.6 to 7.8 times as large as that in the contralateral unoperated stifle. The addition of HA decreased the elevated values in three of the four ACL-transected joints. Conclusion. Friction was higher in the OA joints than in the healthy joints. The addition of HA was effective in the early stage of OA represented by papain injected case, while its effect seems not to be evident for advanced OA produced ACL transection which accompanies macroscopic shape changes.