Leslie Ian, Williams Sophie, Isaac Graham, Hatto Peter, Ingham Eileen, Fisher John
Institute of Medical and Biological Engineering, University of Leeds, Leeds, UK.
Proc Inst Mech Eng H. 2013 Apr;227(4):345-9. doi: 10.1177/0954411912468542. Epub 2012 Dec 6.
Clinical studies have found high wear rates, elevated ion levels and high revision rates of large-diameter metal-on-metal surface replacement bearings in some patients, which have been associated with edge loading of the head on the rim of the cup. We have simulated increased wear and ion levels in metal-on-metal bearings in vitro by introducing variations in translational and rotational positioning of the components, which reproduces stripe wear on the femoral head, cup rim wear and clinically relevant large as well as small wear particles. There is interest in technologies such as surface engineering, which might reduce metal wear and the release of wear particles and ions. Reduced wear with surface-engineered surface replacements compared to metal-on-metal controls has been reported under standard walking conditions with correctly aligned and concentric components. In this in vitro study, the wear of chromium nitride surface-engineered metal-on-metal bearings under conditions of microseparation associated with translational and rotational malpositioning of the components was investigated and the results were compared with a previously reported study of metal-on-metal bearings under the same conditions. Simulations were conducted using our unique hip simulation microseparation methodologies, which reproduce accelerated wear in metal-on-metal bearings and have previously been clinically validated with ceramic-on-ceramic bearings. Four of the six surface-engineered bearings had evidence of head contact on the rim of the cup, which produced stripe wear on the femoral head. Four of the six surface-engineered bearings (two without stripe and two with stripe wear) had lower wear than the previously reported high wearing metal-on-metal bearings. At 2 million cycles, two of the surface-engineered bearings had substantially increased wear rates, four times higher than the high wear rates previously reported for metal-on-metal bearings under the same conditions. There was wear through and cohesive failure of the thick atomic emission physical vapour deposition (AEPVD) chromium nitride (CrN) coating. At this point, the study was stopped to investigate the failure mode. This study highlights the need to pre-clinically investigate the tribology of new bearings under a wide set of clinical conditions as demonstrated by our stratified approach for enhanced reliability (SAFER) simulation methods. In adopting this SAFER approach to pre-clinical simulation testing of new bearings, it is important to communicate the failures as well as successes of technologies arising from the research, in order that the wider community can benefit from the analysis of the pre-clinical failure modes.
临床研究发现，一些患者体内大直径金属对金属表面置换轴承的磨损率高、离子水平升高且翻修率高，这与股骨头在髋臼杯边缘的边缘负荷有关。我们通过引入部件平移和旋转定位的变化，在体外模拟了金属对金属轴承中磨损增加和离子水平升高的情况，这重现了股骨头的条纹磨损、髋臼杯边缘磨损以及临床上相关的大、小磨损颗粒。人们对表面工程等技术很感兴趣，这些技术可能会减少金属磨损以及磨损颗粒和离子的释放。据报道，在标准行走条件下，部件正确对齐且同心时，与金属对金属对照相比，表面工程处理的表面置换的磨损有所减少。在这项体外研究中，研究了在与部件平移和旋转位置不当相关的微分离条件下，氮化铬表面工程处理的金属对金属轴承的磨损情况，并将结果与先前报道的在相同条件下金属对金属轴承的研究进行了比较。使用我们独特的髋关节模拟微分离方法进行模拟，该方法可重现金属对金属轴承中的加速磨损，并且先前已在陶瓷对陶瓷轴承上得到临床验证。六个表面工程处理的轴承中有四个有股骨头与髋臼杯边缘接触的迹象，这在股骨头上产生了条纹磨损。六个表面工程处理的轴承中有四个（两个无条纹磨损，两个有条纹磨损）的磨损低于先前报道的高磨损金属对金属轴承。在两百万次循环时，两个表面工程处理的轴承磨损率大幅增加，比先前报道的在相同条件下金属对金属轴承的高磨损率高出四倍。厚原子发射物理气相沉积（AEPVD）氮化铬（CrN）涂层出现了磨损穿透和内聚性失效。此时，研究停止以调查失效模式。这项研究强调了需要在广泛的临床条件下对新轴承的摩擦学进行临床前研究，正如我们的增强可靠性分层方法（SAFER）模拟方法所证明的那样。在采用这种SAFER方法对新轴承进行临床前模拟测试时，重要的是要传达研究中出现的技术的失败和成功情况，以便更广泛的群体能够从临床前失效模式的分析中受益。
