Galvanic corrosion in modular THRs: correlating in-vitro test results to observations from retrieval analyses

Recent retrieval analyses of Ti-6Al-4V/Co-Cr-Mo modular hip prostheses which have been in situ for more 15 years are raising concerns regarding accelerated corrosion at this interface. This concern is compounded by the fact that the accelerated corrosion may be mediated by both mechanical and electrochemical factors. The aim of this study was to evaluate the influence of a predominantly galvanic stimulus on the corrosion performance of mixed metal modular total hip replacements (THRs). The first part of this study used a sequence of static in vitro galvanic corrosion tests to determine the susceptibility of this couple to galvanic corrosion. The conclusions obtained from the in vitro study were tested by retrieval analyses on captured assembly THRs (Sivash and SRN Type ^S Surgical Corporation). Their femoral components were thermomechanically assembled (to preclude fretting) and were ideal for examining the effect of a predominantly galvanic stimulus on the alloy couple. The in vitro study and the observations from retrieval analyses corroborate the fact that a stimulus of purely galvanic etiology will not initiate accelerated corrosion at this interface. It would however be a significant factor under conditions of a priori mechanical damage to the interface