Real-time corrosion measurements to assess biotribocorrosion mechanisms with a hip simulator

Due to the reduced wear compared to the metal-on-polyethylene implant, second generation metal-on-metal hip prostheses have been widely used as the replacement in younger patients in recent years. Osteolysis induced by polyethylene wear debris was a major concern with metal-on-polyethylene hip replacements. In metal-on-metal total joint replacements, however, there has been concern about the incidents of pseudo tumours as a result of the production of very fine wear debris and the associated production of metallic ions of Co and Cr. The origins of the metallic ions may be from two potential sources: from the bearing surface and from the dissolution of wear debris produced by the tribological action or the production of ions by depassivation of the CoCr alloys. gh there has been extensive work on simulation of wear processes in hip joint replacements through hip simulators running over prolonged periods and mapping the wear rates, to date there have been several attempts to measure the interactions (biotribocorrosion) between corrosion and tribology in-situ in simulated body fluids using a hip simulator. This paper describes the instrumentation of an integrated hip joint simulator to provide electrochemical measurements in real-time. The open circuit potential and polarization experiment results are reported and the importance of these measurements to gain an understanding of the origins of metal ions and to complement the wealth of wear data available is discussed.