Possible reasons for the unexpected bad biocompatibility of metal-on-metal hip implants

BackgroundUncemented titanium hip prostheses with a metal-on-metal bearing combination have recently shown an unexpected bad biocompatibility. The cause for the problems has not be found so far. In this work, a connection between scratches on the stem created during insertion and medical complications is assumed. In particular, enduring electrochemical processes at the scratched parts of the surface (involving aluminium and chromium) may give rise to troubles.MethodsElectrochemical impedance spectroscopy (EIS) has been used in order to investigate the chemical processes at the surface in electrolytic environment. Bode and Nyquist diagrams have been measured.ResultsChemical processes take place at the scratches even after repassivation seems to be finished. Aluminium is continuously released, chromium is built into the metal matrix.ConclusionsThe observed processes may be the cause for bad biocompatibility and the observed medical complications with the implants.