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There is now considerable interest in metal-on-metal bearings for hip prostheses. Extremely low wear rates (0.1 mm3/10(6) cycles) have been reported in some simulator studies, while in vivo studies, although still very low, have shown wear rates of the order of 1 mm3/10(6) cycles. The aim of this study was to compare wear rates of metal-on-metal bearings in two hip simulators with different kinematic inputs. In the simulator with three independent input motions which produced an open elliptical wear path with a low level of eccentricity, the wear rates were very low as recorded previously in other simulators. In the simulator with two input motions which produced an open elliptical wear path with greater eccentricity the wear rate was at least ten times higher and closer to clinical values. The motion and kinematic conditions in the contact are critical determinants of wear in metal-on-metal bearings.

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a b s t r a c tIn order to investigate the effect PMMA bone cement chemistry has on the fretting corrosion of cemented femoral stems, a novel test setup with integrated electrochemistry was developed and conducted in part reference to ISO 7206-4:2010. Ultima TPS TM femoral stems were cemented into a specially prepared delrin moulds using a third generation cementing technique similar to the procedure used in-vivo. Three commercially available PMMA bone cements were tested in order to understand the role bone cement chemistry plays on the fretting-corrosion rates at the stem-cement interface. Each stem-cement component was then orientated and set in place using laboratory grade PMMA cement, immersed in 0.9% NaCl and subjected to 500,000 cycles of cyclic loading at 1 Hz. Intermittent Open Circuit Potential (OCP) and Linear Polarisation Resistance (LPR) measurements were conducted in order to assess the effect PMMA bone cement chemistry has on the localised dissolution of cemented femoral stems. Macroscopic observation and scanning electron microscopy with integrated energy dispersive X-ray analysis (SEM/EDX) was conducted in order to support the electrochemical findings.Crown