Characterization of solid products of corrosion generated by modular-head femoral stems of different designs and materials

This paper reviews the microanalytic and histopathologic findings from studies reported previously by our laboratory describing the nature and significance of solid products of corrosion generated at modular junctions of femoral components for hip replacement. A total of twenty-five retrieved, corroded modular junctions with surrounding tissues were examined from a variety of component designs and material combinations, including head/neck couples of CoCr/CoCr, CoCr/Ti6A14V, and Al₂O₃/CoCr. The products were examined using electron microprobe with energy-dispersive x-ray analysis, x-ray diffraction, and Fourier-transform infrared spectroscopy. The products of corrosion identified at the modular junctions of all of the various prostheses examined were similar regardless of the implant design or materials coupled, even when a ceramic head was employed. The most prevalent corrosion product was characterized as an amorphous chromium orthophosphate hydrate-rich material. Particles of this material were identified throughout the periprosthetic tissues of most of the cases studied and at the polyethylene bearing surface of several cases. The multitude of particles generated by fragmentation of the corrosion products and the finding that they migrate to sites distant from their origin are of concern because of their potential to increase the production of polyethylene wear debris by a three-body wear mechanism and their direct participation in particle-induced, macrophage-mediated osteolysis.