Measurements of friction in degenerated joints by a robotic arm

分别用木瓜蛋白酶注射法和前交叉韧带（ACL）切断法对兔膝关节进行表面磨损，观察膝关节的润滑能力。此外，我们估计在何种程度上的关节润滑能力的恢复，通过添加透明质酸（HA）。作为润滑能力的参数的关节摩擦力由设计成使用通用力传感器的市售机器人臂的系统测量。通过机械臂和力传感器的回路进行力控制，使股骨髁在胫骨平台上平稳滑动。在10 N的静态载荷作用下，测定了兔膝关节的启动摩擦系数。用成年日本白色家兔制作膝关节软骨退变模型，在关节软骨内注射0.1%透明质酸溶液后重复测量。我们使用了5个磨损模型、9个木瓜蛋白酶注射模型和3个ACL韧带切断模型，在所有三个模型中，平均摩擦系数随着负荷持续时间显著增加。当衰退时间超过600 s时，退化膝关节的平均摩擦系数是对照膝关节的2倍。在150 s时，韧带切断模型的平均摩擦系数最高。在150 s的加载时间内，软骨的变性程度与软骨的润滑能力呈良好的相关性。此外，在磨损模型和ACL韧带切断模型中，HA的注射使摩擦系数值恢复到约0.1的范围。

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.