A Basic Study of Sealed Joint with Artificial Synovial Fluid

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Basic characteristics of a novel sealed type artificial joint was investigated. The results show that the wear rate of HDPE socket may be drastically reduced due to the lubrication effect of synthetic synovial fluid. Since the artificial joint capsule trapps the wear particles, biological reaction against HDPE particles is completely protected. The purpose of this study was to investigate the possible design of a sealed joint for long term use. The results of this reserach project is as follows ;(1) Two types of artificial joint capsule of silicon rubber or polyurethane were produced by casting. The sealing performamce of these capsules were tested for several kinds of liquid.(2) The range of flexion-extension angle of the sealed joint exceeded 80degrees, and that of external-internal rotation exceeded 40degrees. Joint capsule of both materials showed sufficient deformability not to limit the joint movement, while the joint capsule of silicon rubber showed better deform ability.(3) For large deformation, the resisting moment showed non-linear characteristics. At the same time, buckling phenomenon was observed with wrinkles on its surface.(4) Since large moment was measured near the center of the joint capsule, it is necessary to thicken this place.(5) Wear test was performed with several liquids containing castor oil with a pin-on disk apparatus. The friction coefficient was reduced to be 0.02 with castor oil, and wear rate with castor oil was less than 1/10 of that with bovine serum.