Investigation of wear and corrosion products released from the CoCrMo tapers and cement-stem interface in total hip replacements

Adverse local tissue reactions (ALTRs) to solid and soluble debris released from cobaltchromium-molybdenum (CoCrMo) alloy metal-on-metal (MoM) hip replacements have been raising numerous concerns and currently represent the main reason for MoM revision surgery. The introduction of modularity at the femoral components has further contributed to the increasing incidence of body responses to the implant, due to the wear and corrosion of the metallic tapers. Products originating from the secondary metallic interfaces, such as tapers or cement-stem interfaces, were suggested to elicit more severe body responses to the implant than the equivalent dose of debris from the bearing surfaces. Body responses are dictated by the interaction of the particles with the biological environment, and highly depend on the particle size, morphology, aggregation state, chemical composition and speciation. Despite the increasing evidence of ALTRs to metal debris originating from the tapers or cement-stem interfaces, little is known about these products and their characteristics. There have been numerous reports of black and flaky deposits of debris around the revised tapers or cement-stem interfaces, which were confirmed to be metallic by analytical techniques. The speciation of CoCrMo taper debris has only been reported for debris in periprosthetic tissue or spread at distant organs, which may have been altered by the specific biological environments at these sites. The present study reveals the nature of debris released in vivo from the mixed (CoCrMo/Ti alloy) and matched (CoCrMo/CoCrMo alloy) tapers and CoCrMo cement-stem interfaces. The implants used in this study have been retrieved from patients at the time of revision surgery and have been forensically examined to understand the main wear and corrosion processes responsible for their failure. The wear and corrosion flakes were comprehensively characterised from the micro scale down to the nano level, to understand their structural and chemical features and reveal the constituent building blocks. Two different methods were used to clean the debris and their effects on the particle characteristics were assessed. The study is the first to reveal the size, elemental composition and speciation of debris from the mixed and matched material tapers and cement-stem interfaces, by using complementary state-of-the-art characterisation techniques. The study compared the physicochemical characteristics of debris released from CoCrMo tapers and stems, and debris from mixed and matched material taper junctions, and revealed significant size differences which may influence the adverse body responses to the implant. The speciation analysis revealed chemical species whose effects on the cells have not been previously assessed and may be linked to the increased in vivo reactivity of the CoCrMo debris from tapers and cement-stem interfaces.