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1.1 The objective of this guide is to advise researchers on the possible high demand wear test features that should be included in evaluation of hard on hard articulations. This guide makes suggestions of what high demand test features may need to be added to an overall high demand wear test regime. Device articulating components manufactured from other metallic alloys, ceramics or with coated or elementally modified surfaces could possibly be evaluated with this guide. However such materials may include risks and failure mechanisms which are not adressed in this guide.

1.2 Hard-on-hard hip bearing systems include metal-on-metal, ceramic-on-ceramic, ceramic-on-metal, or any other bearing systems where both the head and cup components have high surface hardness. An argument has been made that the hard-on-hard THR articulation may be better for younger more active patients. These younger patients may be more physically fit and expect to be able to perform more energetic activities. Consequently, new designs of hard-on-hard THR articulations may have some implantations subjected to more demanding and longer wear performance requirements.

1.3 Total Hip Replacement (THR) with metal-on-metal articulations have been used clinically for more than 50 years (1, 2).2 Early designs had mixed clinical results. Eventually they were eclipsed by THR systems using metal on polyethylene articulations. In the 1990s the metal-on-metal articulation again became popular with more modern designs (3), including surface replacement.

1.4 In the 1970s the first ceramic-on-ceramic THR articulations were used. In general, the early results were not satisfactory (4, 5). Improvement in alumina, and new designs in the 1990s improved the results for ceramic-on-ceramic articulations (6).

1.5 The values stated in SI units are to be regarded as the standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

5.1 The current hip simulator wear test standards (ISO 14242 Part 1 or Part 3) stipulate only one load wave form and one set of articulation motions. There is a need for more versatile and rigorous wear test regimes, but the knowledge of what represents realistic high demand wear test features is limited. More research is clearly needed before a standard can be written that defines what a representative high demand wear test should include. The objective of this guide is to advise researchers on the possible high demand wear test features that should be included in evaluation of hard-on-hard articulations.

5.2 This guide makes suggestions of what high demand test features may need to be added to an overall high demand wear test regime. The features described here are not meant to be all inclusive. Based on current knowledge they appear to be relevant to adverse conditions that can occur in clinical use.

5.3 All the test features, both conventional and high demand could have interactive effects on the wear of the components.