Bioimplantation of Metals in Patients with Metal Allergy: The Late Outcome

Of 212 patients undergoing total hip replacement who were tested preoperatively for sensitivity to nickel, chromium, and cobalt, fourteen showed sensitivity. No sensitivity to the bone cement was recorded. Of 173 patients who had never had a metal implant before, 5.8 per cent showed a positive reaction. Two patients out of fifteen with a failed McKee-Farrar prosthesis were found to be sensitive. Of six patients who had a stable McKee-Farrar prosthesis in the other hip, none showed sensitivity to the metal. In four of sixty-six patients, sensitivity to nickel or cobalt developed after the implantation of a metal-to-plastic prosthesis. No patients were sensitized to the cement. The consequences of proved hypersensitivity in patients with metal-to-plastic prostheses, either present prior to insertion of the prosthesis or evoked by the implant material, are not known.

A prospective study of allergic contact dermatitis after metal-on-plastic total hip replacement was undertaken in 69 patients, of whom 54 were available for review after operation. Before operation six patients were metal sensitive, but only one remained so afterwards; this patient had given a clear history of metal sensitivity and a titanium prosthesis had therefore been used. In all six patients the result of the operation was good and no case of loosening occurred. Sixty-three patients had negative patch tests before operation; in none of these was metal sensitivity detected after operation. Cutaneous sensitivity to various metals is well documented after the insertion of metal-on-metal prostheses and in failed prostheses. We have not found any such increased sensitivity after metal-on-plastic hip replacement. There is little evidence of a direct causal relationship between metal sensitivity and subsequent loosening. The cutaneous sensitivity may be the consequence of loosening rather than its cause. Our results suggest that, providing metal-on-plastic prostheses are used, routine patch testing before hip replacement is no longer required.

A prospective study was made in 85 patients of the relationship between implantation of metal-to-polyethylene hip prostheses and the incidence of delayed-type allergy to components of the prostheses. It shows that sensitization to cobalt, nickel and chromate, and to methacrylate, can develop as a result of such implantation. Loosening did not occur in any of the cases of possible sensitization. Evidence of allergy to prosthetic components was not found in any of the 10 cases of loosening.