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The stress-strain curve of an industrial composite such as a fiber-reinforced plastic falls between those of fibers and plastic matrix. On the other hand, despite the fact that the biological soft tissue is composed of collagen fascicles in a matrix whose Young's modulus is almost negligible, the Young's modulus of the tissue is higher than the fascicles. To insight into the mechanism of such inverse characteristics, we developed a mathematical model of a ligament, by taking into account a fascicle's kinematic non-uniformity along its longitudinal direction and mechanical interaction between fascicles or a fascicle and matrix. Simulations results demonstrated the inverse characteristics and also helped to understand the mechanism of ligament's failure. [ABSTRACT FROM AUTHOR]

The objective of this study is to compare the kinetics and kinematics between the Cruciate Retaining (CR) type and the Posterior Stabilized (PS) type of the artificial knee joints from the results of a 3D mathematical model analysis of knee joint motion. Our 3D model included not only the femur-tibia joint but also the patella-femur joint can introduce variations of contact point trajectories, contact pressure on the articular surfaces. The simulation results demonstrated that, highly stable joint articulation was confirmed for the PS, yet stress concentration or disarticulations was found if the engaging or disengaging between the post and cam did not occur at an appropriate time. [ABSTRACT FROM AUTHOR]

Currently used knee prostheses are broadly classified into the CR type and the PS type. We are planning to develop a new type of knee prosthesis which could make a complete deep knee flexion. Although the new prosthesis should be developed on the basis of the PS rather than the CR, we should further consider about weather we could cut the PCL so readily, and weather high stress concentration might not arise on the articulation surfaces whose conformity is usually so high. Thus we performed simulation analyses subject to the CR instead of the PS, thereby introducing the relationship between the PCL function and the joint articulation conformity. Then making most of the simulation results, we designed a complete flexionable knee prosthesis designated CFK prosthesis. [ABSTRACT FROM AUTHOR]

We have developed a technique for estimating 3D motion of knee prosthesis from its 2D perspective projections. Our estimation algorithm includes some innovations such as a two-step estimation algorithm, incorporative use of a geometric articulation model and an algorithm to solve two silhouettes' overlapping problem. When we attempt to apply our algorithm to a clinical setting, we face a problem such that we can not assess the algorithm because the actual positions and orientations are not known. Thus we built an experimental system using an X-ray photography and a robot for assessing the algorithm. The system is also promising for developing a variety of experiments such as the wear tests of the prosthetic articulating surfaces and the contact stress analyses from photoelastic measurement [ABSTRACT FROM AUTHOR]

We will propose two innovative techniques for estimating 3D motion of the knee prosthesis from its 2D perspective projections such as X-ray images. One of our proposing techniques is a two-step estimation algorithm and the other is a way to solve overlapping problem. In our two-step estimation algorithm, the first step estimation was done, in the same way as Banks and Hodge's on the assumption of orthogonal projection. Then, the second step estimation was succeeded based upon the perspective projection to accomplish more accurate estimation. The other is a novel method to solve such a problem as our algorithm did not function when the silhouettes of tibio and femoral components overlapped with each other. Here the estimation was processed in two steps in associate with the above-mentioned two-step estimation. First, the missing part of silhouette contour due to overlap was interpolated using free-formed curvatures. In the next step, a clipping window was set in the projective coordinate so as to separate the overlapped silhouette. Simulation results demonstrated that our two-step estimation algorithm improved accuracies much, and also sufficient accuracies could be assured even for the overlapped silhouettes; equivalent to those without overlap. [ABSTRACT FROM AUTHOR]