Loosening and Osteolysis Associated with Metal-on-Metal Bearings

Abstract

Over the last several years, many orthopaedic surgeons have embraced so-called alternative bearing surfaces in total hip arthroplasty, largely on the basis of the hypothesis that a reduction in the volumetric wear rates afforded by these improved articulating couples will reduce the prevalence of osteolysis and aseptic loosening, which in turn will improve implant survivorship. The articles by Korovessis et al.1 and Milosev et al.2 in this issue of The Journal provide valuable new data on the intermediate-term performance of one metal-on-metal-bearing hip-replacement system. These studies show that this particular metal-on-metal system is not immune to osteolysis and aseptic loosening and further suggest that osteolysis and aseptic loosening may be mediated, at least in part, by an adaptive immune response (metal hypersensitivity) independent of, or in concert with, the relatively well-characterized innate immune response (particle-stimulated macrophage, fibroblast, and osteoblast-mediated inflammatory bone loss) typically associated with periprosthetic osteolysis3. Metal hypersensitivity-induced osteolysis and aseptic loosening represent underappreciated and incompletely understood mechanisms of implant failure. How strong is the evidence that the failures in these two cohorts at the time of intermediate-term follow-up (at a mean of seventy-seven months and eighty-five months) were due to metal hypersensitivity? It should be clearly understood that, at present, the evidence linking osteolysis and aseptic loosening with metal …