MIGRATION OF CORROSION PRODUCTS FROM MODULAR HIP PROSTHESES - PARTICLE MICROANALYSIS AND HISTOPATHOLOGICAL FINDINGS

Migration of solid corrosion products from the modular head-neck junct ion of fifteen total hip replacements to the periprosthetic tissues wa s sturdied. The devices and tissues were recovered at the time of a re vision procedure or at autopsy after a mean of sixty-four months (rang e, eight to ninety-seven months). The prostheses had a cobalt-chromium -alloly head coupled with a cobalt-chromium-alloy or a titanium-alloy stem. The solid corrosion product was identified by electron microprob e analysis and Fourier transform infrared microprobe spectroscopy as a chromium orthophosphate hydrate-rich material. The product was presen t 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 bearing surfa ce. The particles in the tissues ranged in size from less than one to 500 micrometers. They were present within histiocytes or were surround ed by foreign-body giant cells in the pseudocapsule of the hip joint; in the membranes of the femoral bone-implant interface; and at sites o f femoral endosteal erosions, with and,without loosening of the femora l 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. Fragm ents of these corrosion products increase the particulate debris in th e joint and migrate along membranes at the bone-implant interface to s ites remote from their origin. They can also migrate to the prosthetic bearing surface, where they may be a component in three-body wear, th ereby increasing the production of polyethylene debris. All of these f actors can contribute to periprosthetic loss of bone and aseptic loose ning. The potential for systemic toxicity is not known.