Measurement of Knee Joint Motions in Deep Flexions for Optimal Design of Polycentric Assistive Device and Prototype of Adjustable Knee Assist

Motions of a knee joint occur between the femur and the tibia and involve sliding and rolling, in which its rotational center dramatically moves, particularly during deep flexions. In our previous study, we developed a polycentric biomimetic knee joint (PC-BKJ), using two gears with the same modules but different radii, as an assistive device for knee joints to assist knee motions including deep flexions. However, in our previous study, the PC-BKJ was developed based on knee motion data from the literature, which do not fit other individuals. Therefore, to achieve tailor-made devices that fit the knee motions of wearers well, we analyzed the relative motions of five healthy knee joints during squatting motions using an optical motion capture system to estimate the positions of the rotational centers. The experimental results showed that the movement trajectories of the centers of rotation were approximately 50–60 mm and 40–50 mm in the horizontal and vertical directions, respectively. In addition, based on the results, the optimal radius for the PC-BKJ was determined for the knee of each subject and examined.