The goals of this research are to establish criteria for damage occurring to articulating surfaces of total joint replacement components fabricated from ultra high molecular weight polyethylene (hereafter referred to simply as polyethylene) and to apply these criteria in optimizing implant design. Based on observations of retrieved implants and experimental and analytical determinations of the stresses occurring on and within components of contemporary total joint replacement designs, the following hypotheses specifically formulated to apply to knee joint geometry have been developed: Hypothesis 1: The type and extent of damage to the articulating surface of polyethylene joint components is directly related to the presence (sliding) or absence (rolling) of surface velocity of the mating component relative to the polyethylene. Hypothesis 2: The type and extent of damage to the articulating surface of polyethylene joint components is directly related to the geometry and conformity of the articulating surfaces and to the thickness of the polyethylene component. Hypothesis 3: The type and extent of damage to the articulating surface of polyethylene joint components is directly related to post manufacture treatments of the bulk polyethylene affecting consolidation, elastic modulus, and yield stress. To test these three hypotheses, an experimental loading apparatus will be used to examine the effect of single test variables on the damage occurring to polyethylene specimens. Observations and measurements made on the specimens will characterize the type and extent of damage sustained by the polyethylene. Results from finite element analyses will be used to establish appropriate specimen geometries and to correlate the observed damage with the predicted stress distributions in the specimens.
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