The Role of Mechanically Activated Area on Tribocorrosion of CoCrMo
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TRODUCTION
OSTEOARTICULAR implants for hip replacements have become one of the most significant surgical advances of the last century. According to different Governmental Agencies, more than 300,000 total hip replacements (THR) are performed each year in the United States[1,2] of which 27 percent involve metal-onmetal (MoM) devices. Among others, Co-Cr-Mo alloys are considered to be the most used alloys for orthopedic implants because of their excellent corrosion resistance, mechanical properties, and biocompatibility. In early 2012, after a detailed study, based on the UK National Joint Registry for 402,051 hip replacements of which 31,171 were stemmed MoM, suggested this kind of stemmed prostheses was associated with high failure rates compared with ceramic-on-ceramic prostheses.[3] As a consequence, those authors recommend that MoM-bearing surfaces should not be used in stemmed THR. Although the just cited article has been the subject of some controversy,[4] there is no doubt that patients implanted with these hips could develop progressive soft tissue reactions to the wear debris associated with MoM articulations. The Medicines and Healthcare products Regulatory Agency (MHRA) issued a ‘‘medical device alert’’ to monitor the blood metal ion levels (Co and Cr) for patients implanted with MoM hip replacements.[5] MARIA ANGELES ARENAS, Tenured Scientist, ANA CONDE, Research Scientist, and JUAN J. DE DAMBORENEA, Research Professor, are with the Department of Surface Engineering, Corrosion and Durability, National Centre for Metallurgical Research (CENIM), Spanish National Research Council (CSIC), Avenida de Gregorio del Amo, 8, 28040 Madrid, Spain. Contact e-mail: [email protected] Manuscript submitted February 4, 2013. Article published online April 26, 2013 4382—VOLUME 44A, SEPTEMBER 2013
It is very widely reported that metal ion release into the bloodstream as well as wear debris can cause soft tissue necrosis in bone and tissue around the hip.[6,7] Concerns about the negative effects of ion release promoted a general shift in the early 1970s to cemented metal-onplastic hips, although by the end of that decade, new worries about the biocompatibility of the cement and the effect of polyethylene wear particles led to a resurgence of MoM combinations.[8] As MoM produces a significantly higher release of metal ions in comparison with other bearings, there is a need for further study of the tribocorrosion of MoM bearings.[9–12] Although there is a large literature on corrosion properties of CoCrMo alloys,[13] a few articles are focused on the synergistic effect of corrosion and wear in a simulated physiological solution. Even fewer articles have focused on the contribution of the active area generated during wear tests. This knowledge is necessary to aid us in the further improvement of the behavior of these types of prostheses. In the current article, an interpretation of the tribocorrosion mechanism of CoCrMo alloys is developed using electrochemical measurements, linking the active testing area with the current and po
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