Measurements of friction in degenerated joints by a robotic arm

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We estimated the lubrication ability of rabbit stifles that were degenerated by the abrasion of the surface layer papain injection and desmotomy of anterior cruciate ligament (ACL), respectively. Furthermore we estimated the extent to which the joint lubricating ability is restored by the addition of hyaluronic acid (HA). Joint friction as a parameter of the lubrication ability was measured by a system that was designed so a commercially available robotic arm using a universal force sensor. The force control by the loop of the robotic arm and the force sensor made the femoral condyle slide smoothly on the tibial plateau. The start-up coefficient of friction in the rabbit stifle was measured after some different periods of stationary load of 10 N. We repeated the measurements after the injection of the solution of0.1 % hyaluronic acid into the articular cartilage.We used adult Japanese white rabbits to make the degenerated stifles. We used 5 abrasion models, 9 papain injection models, and 3 ACL desmotomy models.At all three models, the average coefficient of friction significantly increased with loading duration. When fading duration surpassed 600 s, the average coefficient of friction of degenerated stifles was twice as lame as that of the control stifles. At the 150 s loading duration, the average coefficient of friction of the ACL desmotomy models was highest among these three. Followed in order by those of the papain injection models and the abrasion models.The degeneration level of cartilage appeared to correlate well with lubrication ability at 150 s loading duration. Additionally, the injection of HA recovered the value of coefficient of friction to the range about 0.1 in the models of abrasion and ACL desmotomy models.