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Electrochemical instrumentation of a hip simulator: a new tool for assessing the role of corrosion in metal-on-metal hip joints

These first in-situ electrochemical measurements on an instrumented hip joint simulator enabled estimates to be made of the contribution of corrosion to total material degradation in metal-on-metal hip replacements. Ion release was considerably less than in simple laboratory machines, suggesting that lubricating films were partially protecting the bearing surfaces throughout much of the cycle. Milder conditions at the interacting bearing surfaces encouraged the formation of protective tribofilms consisting of organo-metallic species. Evidence of ennoblement after about 100,000 cycles, reflected gradual running-in. This significant study opened the way to quantify separate contributions to bearing degradation of mechanical wear and corrosion.