Metal ion hypersensitivity in metal-on-metal hip arthroplasty

Total hip arthroplasty with use of metal-on-metal bearings has been reintroduced as an alternative to metal-on-polyethylene bearings because of theoretical advantages such as reduced wear and a lower prevalence of osteolysis. However, we have observed early osteolysis in nine patients (ten hips) out of 165 patients (169 hips) who had been managed with total hip replacements using a contemporary metal-on-metal hip design and investigated the possible etiologic role of metal hypersensitivity. The nine patients who had an osteolytic lesion had a significantly higher prevalence of hypersensitivity to cobalt, as determined by patch testing, when compared to nine controls (p = 0.031). The retrieved periprosthetic tissues from the two revised hips showed no evidence of metallic staining, but microscopic analysis revealed a perivascular accumulation of CID3-positive T-cells and CD68-positive macrophages, and an absence of both particle-laden macrophages and polymorphonuclear cells. Immunohistochemical analysis demonstrated that potent bone-resorbing cytokines such as IL-1 beta and TNF-alpha were produced mainly by infiltrated lymphocytes and activated macrophages. These findings raise the possibility that early osteolysis in this second-generation metal-on-metal hip replacement is associated with abnormalities consistent with delayed-type hypersensitivity to metal.