Charnley wear model for validation of hip simulators' ball diameter versus polytetrafluoroethylene and polyethylene wear

Abstract

Wear rates of polytetrafluoroethylene (PTFE) and polyethylene cups were compared in 9-channel and 12-channel simulators, using serum lubrication and gravimetric techniques for wear assessment. Cobalt-chromium (CoCr) and alumina ceramic femoral heads in 22-42 mm diameter range were used to validate simulator wear rates against clinical data. This was also the first study of three femoral head sizes evaluated concurrently 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 linear as a function of test duration. Precision within each set of three cups was within +/-6 per cent. The wear rates from experiments repeated over 15 months were reproducible to within +/-24 per cent. However, the magnitudes of the simulator wear rates were not clinically accurate, the PTFE wear rates (2843 mm3/10(6) cycles; 22 mm diameter) were over three times higher than in vivo, the polyethylene 30 to 50 per cent on the low side (23 mm3/10(6) cycles; 22 mm diameter). Volumetric wear rate increased with respect to size of femoral head and a linearly increasing relationship of 7 8 per cent/mm was evident with respect to femoral head diameter for both PTFE and polyethylene. These data compared well with the clinical data.

Wear of ultra-high molecular weight polyethylene and polytetrafluoroethylene in a hip simulator: A dose-response study of protein concentration

“…In contrast, the PE wear-magnitudes showed a decreasing trend from 3 to 63 mg/mL protein concentration, which was also reported by Wang et al (1998) and Liao et al (1996). In all serum-lubricated tests, both PTFE and PE exhibited increased wear with increased head-diameter, which was consistent with previous studies (Good et al 1996, Clarke et al 1997, Bragdon et al 1998). …”

“…Contemporary simulator studies, using bovine serum as the lubricant, have shown PE wear-rates lower than the clinical rates (Livermore et al 1990, Kabo et al 1993, Saikko, 1993, Callaghan et al 1995, Bragdon et al 1996, Clarke et al 1997, McKellop et al 1997, Jasty et al 1997 and PTFE wear-rates 4 times higher than the clinical rates (Clarke et al 1995, Good et al 1996. Waterlubricated tests of both materials showed wearrates much lower than the clinical rates (Saikko 1993, Clarke et al 1995, Good et al 1996, Phipatanakul et al 1998).…”

“…This same head-size effect has now been reported clinically for PE cups (Livermore et al 1990, Jasty et al 1997. The ball-size effect for both PTFE and PE has been duplicated in the laboratory with serum lubrication (Good et al 1996, Clarke et al 1997. However, in water-lubricated tests the wear-rates were 4 times lower than clinical and the ball-size effect was lost (Good et al 1996, Phipatanakul et al 1998.…”

Potential thermal artifacts in hip joint wear simulators

“…15,16 Similar machines are in use in a number of laboratories. [17][18][19] To stabilize the test conditions, the specimens were run for 1 million cycles before the temperatures were recorded. The wear rates of the cups, measured by weight loss during the interval from 0.5 to 1.0 million cycles, were comparable to those of a previous study 20 for each of the three material combinations.…”

Wear simulation of UHMWPE for total hip replacement with a multidirectional motion pin-on-disk device: Effects of counterface material, contact area, and lubricant

“…11 Before the CTPOD device, the production of realistic wear was possible only with complex and expensive devices, such as hip joint simulators. 8,[12][13][14][15] Irradiation can change the wear behavior of polyethylene drastically. 16,17 To rule out the effects of sterilization, nonsterilized ultra-high molecular weight polyethylene was used.…”