Effects of hip-loading input on simulated wear of Al2O3-PTFE materials

The objective of this study was to compare the effects of static, sinusoida l and physiological load-profiles on wear of Al2O3-PTFE materials. This was an accelerated wear model of clinical relevance. In nine experiments, the peak load-levels were varied from I to 4 kN in a hip simulator with multi-d irectional kinematics and with bovine serum used as the lubricant. Systemat ic wear differences were checked using three sizes of femoral heads in each experiment. The Paul load-profile used was found to be more aggressive tha n sinusoidal, raising the polytetrafluoroethylene (PTFE) wear-rates by 28%. The PTFE cups showed a very mild response to increased load magnitudes, on ly 11-20% increase evident in volumetric wear per 1 kN increase in load. On e recommendation was that simulator wear-studies adopt a 0.25-2.5 kN Paul l oad-profile as their standard. An experiment with 0.84 kN constant-load als o performed satisfactorily, with PTFE wear-rates actually higher than with the I kN sine and Paul load-profiles. Some wear anomalies were encountered due to the use of serum lubrication. Combinations of large head size, high load-magnitudes, the Paul load-profile and the high serum protein concentra tions used in this study were at times contributing factors. Use of low-pro tein serum solution may be advisable for wear studies, not only to properly simulate the polymeric wear characteristics but also to minimize the degra dation artifacts more prevalent in higher protein-concentrations. (C) 2001 Elsevier Science B.V. All rights reserved.