Rejection of metal to metal prosthesis and skin sensitivity to cobalt

Metal to metal prostheses give satisfactory results in 90% of patients. About half of the failure rate may be due to allergic reaction to the metals involved, particularly cobalt. A total of 35 patients in this unsatisfactory group have been patch-tested; 16 were positive to metals, 13 to cobalt, 4 to nickel, and 2 to chromate. Only two patients showed any skin lesions - one a localized dermatitis round the knee joint from nickel sensitivity, and one to cobalt who had a widespread scattered circular erythematous lesion suggestive of a generalized allergic vasculitis. Patients requiring a metal/metal prosthesis should have a careful history taken for metal sensitivity and be patch-tested with the metals. All the patients in this investigation had metal/metal prostheses and no reaction was seen after metal/high density polyethylene implants. Titanium 318 may be a satisfactory substitute for cobalt chrome alloy if reactions are encountered.