Nontribological corrosion modes dominate wrought CoCrMo acetabular taper corrosion: A retrieval study

Corrosion of modular metal-on-metal acetabular tapers in total hip arthroplasty (THA) systems is often attributed to mechanically driven processes. Recent findings suggest that mechanically assisted crevice corrosion (MACC) might not be the dominant cause of corrosion in shell-liner tapers. This study aims to document and present the corrosion modes observed in metal-metal acetabular liners. Twenty-one retrieved wrought CoCrMo liners were examined using digital optical microscopy (DOM), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Corrosion-related damage was documented in nonengagement taper regions, outside of direct taper contact. Within engagement regions, nonmechanically driven corrosion features (pitting, intergranular corrosion) were observed adjacent to fretting and material transfer, which rely on mechanical contact; corrosion independent of MACC was observed even in contact regions. Corrosion types observed included intergranular corrosion (IGC), pitting attack, phase boundary dissolution, all both outside and inside of taper junctions, and MACC within contact regions of the taper. Typical fretting scars associated with MACC were mostly absent, and were not always associated with corrosion damage where present. Finally, hard phase particles (Mo-Si-O) released from the wrought CoCrMo microstructure had redeposited within regions with material loss. Acetabular taper corrosion modes differ significantly from those in head-neck tapers and are dominated by electrochemically driven processes, not mechanical processes, as indicated by corrosion in noncontact regions. With greater prevalence of dual mobility hip implants, acetabular taper corrosion processes must be understood in order to limit their impact on device performance.