Davidson J A
Orthopaedic Research Department, Smith and Nephew Richards Inc., Memphis, Tennessee 38116.
Clin Orthop Relat Res. 1993 Sep(294):361-78.
The micromechanics of ultra high molecular weight polyethylene (UHMWPE) wear in total hip replacement are very complex. Polyethylene wear from the metal head and debris formation are two common types of wear. There are additional wear-related processes occurring at the metal-bearing surfaces that are not well-known, however. This study outlines these processes, including (1) surface wettability changes, (2) oxidative wear of metal surfaces, (3) microabrasion of metal surfaces from oxide film damage, and (4) surface abrasion from three-body polymethylmethacrylate and bone debris. These processes can contribute to metal ion release and a gradual increase in the roughness of the metal surfaces. This can lead to increased long-term UHMWPE wear. Of the metal alloys currently used in total hip replacements, Co-Cr-Mo alloy is significantly more resistant to roughening processes. Hard, stable, oxide: ceramic surfaces articulating against UHMWPE are essentially immune to these surface-roughening processes, however. In addition, they provide a more wettable surface, further minimizing polyethylene wear relative to metal surfaces. By analyzing metal release rates from metal-polyethylene wear tests, it is shown here that Co-Cr-Mo is gradually removed at a rate of about 0.1 micron per year (10(6) cycles), whereas 316L stainless steel is removed on the order of 0.2 microns per year and Ti-6Al-4V on the order of 1 micron per year. The wear rate of Co-Cr-Mo articulating against itself is reported to be still greater, at about 2-4 microns per year after an initial wear-in period. Because metal is gradually removed with articulation time, surface-hardening methods such as nitrogen ion implantation can be expected to provide only temporary resistance to these metal removal and surface-roughening processes. Hard, stable ceramic surfaces such as Al2O3 and ZrO2, however, can be expected to maintain their initial surface finish and thus minimize UHMWPE wear in the long term.
全髋关节置换中超高分子量聚乙烯（UHMWPE）磨损的微观力学非常复杂。金属股骨头导致的聚乙烯磨损和碎屑形成是两种常见的磨损类型。然而，在金属承重表面还发生着其他一些与磨损相关但尚不为人熟知的过程。本研究概述了这些过程，包括：（1）表面润湿性变化；（2）金属表面的氧化磨损；（3）氧化膜损伤导致的金属表面微磨损；（4）三体聚甲基丙烯酸甲酯和骨碎屑导致的表面磨损。这些过程会导致金属离子释放以及金属表面粗糙度逐渐增加。这可能会导致UHMWPE长期磨损增加。在目前用于全髋关节置换的金属合金中，钴铬钼合金对表面粗糙化过程的抵抗力明显更强。然而，与UHMWPE相接触的坚硬、稳定的氧化物：陶瓷表面基本上不受这些表面粗糙化过程的影响。此外，它们提供了更具润湿性的表面，相对于金属表面进一步减少了聚乙烯磨损。通过分析金属 - 聚乙烯磨损试验中的金属释放速率，结果表明钴铬钼合金每年以约0.1微米的速率逐渐磨损（10⁶次循环），而316L不锈钢每年磨损约0.2微米，钛合金Ti - 6Al - 4V每年磨损约1微米。据报道，钴铬钼合金自身相互摩擦的磨损速率更高，在初始磨合阶段后约为每年2 - 4微米。由于金属会随着关节活动时间逐渐磨损，诸如氮离子注入等表面硬化方法预计只能暂时抵抗这些金属磨损和表面粗糙化过程。然而，诸如Al₂O₃和ZrO₂等坚硬、稳定的陶瓷表面预计能够保持其初始表面光洁度，从而从长期来看使UHMWPE磨损最小化。
