Kinematic analysis of artificial knee implants using markers embedded in a bone

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1. Pose estimation of the knee implantTo assess the accuracy of the proposed method, we carried on the in vitro experiments as follows. The tibial component was fixed on a plastic block which was used as a substitute of a bone and four markers were embedded in the plastic block. Radiographs of the component were taken with the frame that comprised of eight calibration markers. Then we determined the local coordinates of markers in the tibial coordinate system. The rms value of errors was O.1 8mm. Once the local coordinates of markers are known. it is possible to estimate pose of the component using information of projected coordinates of markers. The resultant error of rotation and in-plane translation were 0.2° and 0.2 mm, respectively.2. Motion analysis of the mobile bearing knee implantTo assess the motion of an insert of the mobile bearing knee implant, in vitro experiments were carried on as follows. Markers were embedded in an insert and a radiograph was taken. Then motion of an insert was measured using information of projected coordinates of markers, and the error was 0.2 mm. In order to examine the mechanism of the mobile bearing and fixed bearing knee implants, the 3D model of the knee were constructed and simulation study was carried on. During the knee flexion of the fixed bearing knee implant, contact points between a femoral component and an insert moved backward at first, but moved forward slightly. On the other hand, in the case of the mobile bearing knee implant, contact points moved backward monotonically with knee flexion, which resembled natural knee motion.