Biotribocorrosion of metal-on-metal hip replacements: How surface degradation can influence metal ion formation

To investigate the combined effects of wear and corrosion on the performance of metal-on-metal total hip replacements, tribocorrosion tests were performed on 36 mm diameter joint replacements in an instrumented hip simulator. Corrosion related damage contributed significantly to material loss and to the formation of metal ions, and varied throughout the tests. Changes in corrosion rate were attributed to the formation of tribochemical reaction layers. Cyclic variations in corrosion current may be influenced by elastohydrodynamic film thickness, and the presence of these cycles can indicate when the most severe contact is taking place. Additionally, current hip simulator testing procedures, which adequately accelerate the rate of mechanical wear, were found to under-estimate the amount of corrosion damage expected to take place in vivo.