Development of Optimum Design, Trial Production and Evaluation Systems for Knee Joint Prostheses with Artificial Cartilage and Meniscus Similar to Natural Synovial Joints

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The object of this research is to develop the systems for optimum design, trial production and evaluation of knee prostheses with artificial cartilage and meniscus, which have an adaptive multimode lubrication mechanism. The systems for optimum design including geometrical analysis, trial production and simulator testing was developed. The two-channel knee joint simulator was manufactured to simulate the walking motion as three-dimensional mode. Tribological performance of artificial cartilage materials such as hydrogels and polyurethane was evaluated. The rubbing specimens and tibial component of PVA(polyvinylalcohol) hydrogel were prepared by freezing-thawing method. PVA hydrogel with high water content exhibited the lower friction than that with low water content, but the friction increased with repetition of walking cycles. The lubricant constituents, particularly hyaluronic acid and protein had a remarkable effect on friction and wear of compliant materials. It was shown that the … More 5 cycles for freezing-thawing process was the optimum condition to attain the highest stiffness and strength and minimum wear. On the starting friction of compliant material after static loading with different duration, it increased with loading time. The application of high frequency AC electric field was effective in reduction of friction for conductive materials. High water content for PVA hydrogel and the immersion in hyaluronate solution for polyurethane were effective in reducing starting friction.The worn surfaces of polyethylene components for several retrieved knee prostheses of anatomical design were observed, where the delamination and pitting as fatigue wear were discriminated. To elucidate the fatigue wear mechanism, the finite element method was applied as elasto-plastic contact analysis, in which the influence of component thickness and rolling motion on plastic deformation was clarified. From the clinical viewpoint, the kinematic analysis of total knee arthroplasty by pattern matching method was conducted. The changes in knee alignment after total knee arthroplasty and anatomic variation were evaluated.It was shown that geometrical design with better congruity or with appropriate radius, and the application of compliant materials accompanied with boundary lubricating ability enhance the lubricating performance. The design direction including the influence of tensile stress on osteoclast was shown for clinical application. Less