CHARNLEY WEAR MODEL FOR VALIDATION OF HIP SIMULATORS - BALL DIAMETER VERSUS POLYTETRAFLUOROETHYLENE AND POLYETHYLENE WEAR

Wear rates of polytetrafluoroethylene (PTFE) and polyethylene cups wer e compared in 9-channel and 12-channel simulators, using serum lubrica tion and gravimetric techniques for wear assessment. Cobalt-chromium ( CoCr) and alumina ceramic femoral heads in 22-42 mm diameter range wer e used to validate simulator wear rates against clinical data. This wa s also the first study of three femoral head sizes evaluated concurren tly in a simulator (with three replicate specimens) and also the first report in which any wear experiments were repeated. Fluid absorption artefacts were within +/-1 per cent of wear magnitude for PTFE and +/- 8 per cent for polyethylene and were corrected for. Wear rates were li near as a function of test duration. Precision within each set of thre e cups was within +/-6 per cent. The wear rates from experiments repea ted over 15 months were reproducible to within +/-24 per cent. However , the magnitudes of the simulator wear rates were not clinically accur ate, the PTFE wear rates (2843 mm(3)/10(6) cycles; 22 mm diameter) wer e over three times higher than in vine, the polyethylene 30 to 50 per cent on the low side (23 mm(3)/10(6) cycles; 22 mm diameter). Volumetr ic wear rate increased with respect to size of femoral head and a line arly increasing relationship of 7-8 per cent/mm was evident with respe ct to femoral head diameter for both PTFE and polyethylene. These data compared well with the clinical data.