Standard Test Method for Wear Testing of Polymeric Materials Used in Total Joint Prostheses

Abstract

4.1 This test method is intended to be performed in conjunction with pin-on-flat wear machines or similar machines that are designed to evaluate simplified specimen geometries. Note 1: See Haider and Baykal (1)3 for useful considerations and potential pitfalls in conducting pin-on-disk testing, interpreting test results, and the complex and sometimes conflicting effects of lower stress and higher contact area on wear. 4.2 This test method is designed to evaluate combinations of materials with respect to the amount of polymer wear, where quantifiable wear occurs primarily on the polymeric component. With some combinations of materials, significant wear of the counterface may occur, with subsequent embedding of counterface debris particles in the polymer. Such an occurrence will render the weight loss of the polymer specimen unreliable as an indicator of the polymer wear. 4.3 Wear is reported as volume loss of the polymeric specimen as a function of sliding distance; however, if the sliding distance is not constant across the polymeric specimen surface due to complex motion patterns, wear may be reported as volume loss of the polymeric specimen as a function of wear cycles (in which case a “wear cycle” shall be defined). Volume loss of the polymer specimen is determined by dividing the experimental weight loss by the density of the polymer. For ease of interpretation, wear should be reported as a function of both the number of wear cycles and the sliding distance, when possible. 4.4 The reference for the comparative evaluation of candidate materials shall be the wear rate of ultra-high molecular weight polyethylene (UHMWPE) conforming to Specification F648 bearing against counterfaces of cobalt-chromium-molybdenum alloy (in accordance with Specification F75, F799, or F1537), having prosthetic-quality surface finish and lubricated with bovine blood serum (see 5.2).