Migration of corrosion products from modular hip prostheses. Particle microanalysis and histopathological findings

Migration of solid corrosion products from the modular head-neck junction of fifteen total hip replacements to the periprosthetic tissues was studied. The devices and tissues were recovered at the time of a revision procedure or at autopsy after a mean of sixty-four months (range, eight to ninety-seven months). The prostheses had a cobalt-chromium-alloy head coupled with a cobalt-chromium-alloy or a titanium-alloy stem. The solid corrosion product was identified by electron microprobe analysis and Fourier transform infrared microprobe spectroscopy as a chromium orthophosphate hydrate-rich material. The product was present at the junction of the modular head and neck and as particles within the periprosthetic tissues as early as eight months postoperatively. In several hips, it was also present on the polyethylene hearing surface. The particles in the tissues ranged in size from less than one to 500 micrometers. They were present within histiocytes or were surrounded by foreign-body giant cells in the pseudocapsule of the hip joint; in the membranes of the femoral bone-implant interface; and at sites of femoral endosteal erosions, with and without loosening of the femoral component. CLINICAL RELEVANCE: The clinical importance of corrosion at the modular head-neck junction lies, in part, in the effects that solid corrosion products may have on the bone-implant interface. Fragments of these corrosion products increase the particulate debris in the joint and migrate along membranes at the bone-implant interface to sites remote from their origin. They can also migrate to the prosthetic hearing surface, where they may be a component in three-body wear, thereby increasing the production of polyethylene debris. All of these factors can contribute to periprosthetic loss of bone and aseptic loosening. The potential for systemic toxicity is not known.