Development of a Testing Apparatus for Injury of the Knee Ligament Using Robotics. -Application of three Dimensional Displacement Transducer-

我们开发了一种新的膝关节不稳定的仪器测量方法。该测试装置由测试肢体定位支架和铰接式机器人组成。将万能力矩传感器系统(UFS系统)安装在机器人手腕上。UFS系统不仅适用于精确测量施加在小腿上的力，而且还适用于将测试膝关节定位在中立位置。用线性可变位移传感器(LVDT)测量前后位移量。其中一个传感器垫与膝盖骨接触，另一个传感器垫固定在小腿的支撑上。通过机器人对小腿施加60N(6kgf)和80N(8kgf)的前后力。测试对象为屈膝20~30度。该仪器的特点是能直接、非常灵敏地检测测试韧带的僵硬程度。我们用力-位移曲线末端区域的斜率(末端刚度指数)来表示韧带的刚度。正常膝关节在60N力和80N力作用下的前端刚度指数平均值分别为28500N/m和28500N/m，在60N力和80N力时的平均值分别为33600N/m和40900N/m。

We have developed a new method of instrumented measurement for knee instability. The testing apparatus consisted of positioning supports for test limb and an articulated robot. The universal force moment sensor system (UFS system) was attached to the wrist of robot. The UFS system was not only useful for measuring precisely the force applied to lower leg but for positioning test knee in neutral position. The anterior-posterior displacement was measured with linear variable displacement transducer (LVDT). One sensor pad was placed in contact with the patella and the other pad was fixed to the support of lower leg. Anterior and posterior force of 60 N (6 kgf) and 80 N (8 kgf) were applied to lower leg through the robot. The test were performed 20 to 30 degrees of knee flexion. The characteristic feature of our apparatus was that it could detect directly and very sensitively the stiffness of test ligament. We represented the stiffness of ligament by the slope of terminal region of force-displacement curve (terminal stiffness index). The mean of anterior terminal stiffness indexes of normal knees was 28,500 N/m at a force of 60N and 28,500 N/m at a force of 80 N. The mean of posterior terminal stiffness indexes of normal knees was 33,600 N/m at a force of 60 N and 40,900 N/m at a force of 80 N. O) n the other hand, the anterior terminal stiffness indexes of the knee with rupture of anterior cruciate ligament were ranging from 5,600 to 9,300 N/m at forces of 60 N and 80 N.