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A ten-station joint simulator was used to examine the wear properties of 18 total hip prostheses. The wear rates of polyethylene acetabular cups bearing against titanium alloy femoral components were compared to those with either Type 316 stainless steel or cobalt-chrome alloy controls. Three titanium alloy prostheses and three controls were tested from three different manufacturers. Wear was determined by weighing the acetabular cups, using soak-controls to correct for fluid absorption. One million cycles were run under physiological loading, with bovine serum lubrication. For two of the three sets of prostheses, the titanium alloy generated higher mean polyethylene wear rates than the controls. However, the difference was not statistically significant (p > 0.05). The titanium alloy components showed more extensive surface abrasion than either the stainless steel or cobalt-chrome components. This appeared to be an artifact of joint simulator testing, since such extensive surface abrasion was not observed on numerous prostheses removed from patients after several years of use. The third set of titanium alloy prostheses, which had been subjected to a special surface hardening process, showed virtually no surface abrasion, and the mean polyethylene wear rate was identical to that with the cobaltchrome controls. All of the polyethylene wear rates were in the range generally reported for total hip prostheses in clinical use.
prosthetic hips, joint simulator wear tests, clinical wear, titanium alloy, cobalt-chromium-molybdenum implant materials, fatigue (materials), biological degradation
Instructor in Research Orthopaedies, Orthopaedic Biomechanics Laboratory, Division of Orthopaedics, University of Southern California, Los Angeles, CA
Director, Bioengineering Research Institute, Los Angeles, CA