Extract
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.