Measurement of instantaneous center of rotation and its application to the analysis of joint motion

瞬时旋转中心（ICR）的计算方法的发展瞬时旋转中心（ICR）可以用以下几个量来计算：一个点在运动线段上的位置和线段的角度。到目前为止，仅使用连续两次的数量来计算ICR。因此，ICR数据不太可靠。在本研究中，我们提出了基于平滑技术的ICR计算新算法。即，为了确定线段的速度和角速度，我们采用数值低通微分。分析了该方法的误差，讨论了位置数据的最佳采样间隔。通过计算机仿真，将该方法与其他方法进行了比较，验证了该方法具有较高的精度我们制作了一个由位置传感器和个人计算机组成的ICR测量系统。该系统的误差在+3mm以内在颞下颌关节运动中的应用我们将该测量系统应用于颞下颌关节运动。测定习惯性开启和关闭时的ICR位点。这些位点位于髁突下方。根据ICR位置与关节面滑动的关系，表明颞下颌关节的滑动是不可避免的。ICR周围咀嚼肌的力矩臂增加是固定点髁周围咀嚼肌力矩臂的两倍。

1 Development of an algorithm for ICR calculation The instantaneous center of rotation (ICR) can be calculated using following quantities : position of one point on a moving segment and angle of the segment. So far only quantities at two consecutive times were used to calculate ICR. Therefore ICR data have been less reliable. In this investigation, we proposed new algorithm for ICR calculation based on smoothing technique. That is, to determine velocity and angular velocity of a segment, we adopted numerical low-pass differentiation. Then we analyzed error of this method and discussed optimal sampling interval of position data. We compared this method with other methods by computer simulation and verified high accuracy of our method.2 ICR measurement system We made an ICR measurement system composed of a position sensor and a personal computer. The error of this system was within +3mm.3 Application to the tempolomandibular joint motion We applied this measurement system to temporomandibular joint motion. Loci of ICR at habitual opening and closing were measured. These loci were located under the condyle. According to the relationship between location of ICR and sliding at joint surface, it is shown that sliding is inevitable at the tempolomandibular joint. Moment arms of masticatory muscles around the ICR increased as two times of those around a fixed point, the condyle.