On the Formation Mechanism of Column Damage Within Modular Taper Junctions

BackgroundColumn damage is a unique degradation pattern observed in cobalt-chromium-molybdenum (CoCrMo) femoral head taper surfaces that resemble column-like troughs in the proximal-distal direction. We investigate the metallurgical origin of this phenomenon.MethodsThirty-two severely damaged CoCrMo femoral head retrievals from 7 different manufacturers were investigated for the presence of column damage and chemical inhomogeneities within the alloy microstructure via metallographic evaluation of samples sectioned off from the femoral heads.ResultsColumn damage was found to affect 37.5% of the CoCrMo femoral heads in this study. All the column-damaged femoral heads exhibited chemical inhomogeneities within their microstructures, which comprised of regions enriched or depleted in molybdenum and chromium. Column damage appears as a dissolution of the entire surface with preferential corrosion along the molybdenum and chromium depleted regions.ConclusionMolybdenum and chromium depleted zones serve as initiation sites for in vivo corrosion of the taper surface. Through crevice corrosion, the degradation spreads to the adjacent non-compositionally depleted areas of the alloy as well. Future improved alloy and processing recipes are required to ensure no chemical inhomogeneity due to segregation of solute elements are present in CoCrMo femoral heads.