An interesting case of joint prosthesis allergy.

A rare case of contact allergic dermatitis from metal knee joint prostheses is presented. The low incidence of allergic contact dermatitis from metal prostheses is surprising, especially given the frequency of metal allergy, particularly to nickel and cobalt, in the general population. Even patients with known metal allergy often do not react to their metal prosthesis. Systemic allergic contact dermatitis is particularly uncommon with knee joint replacements where the articulation is metal on plastic rather than metal on metal as the former has decreased metal wear debris. In this particular case, there was prior documentation of allergy to both nickel and cobalt, limiting the metal prosthesis options. We used a novel technique using subcutaneous metal implants to determine if this highly metal-sensitive patient would have a postoperative allergic contact reaction to her metal knee joint prosthesis, which contained cobalt and small amounts of nickel.