[Metal allergy to implanted orthopedic prosthesis of the knee from which suppurative drainage persisted].

A 63-year-old Japanese woman who had been taking 5 mg of prednisolone per day for rheumatic arthritis from the age of 23 years underwent surgery on the right knee, during which an orthopedic prosthesis made of an alloy of cobalt (Co) and chromium (Cr) was implanted, in November 2000. Two years and 7 months later, a painful edema developed over the right knee. Although repeated aspiration of the joint yielded a yellow-green fluid, the culture of which was negative, she was given antibacterial drugs. The orthopedic prosthesis of her right knee broke in November 2003, and she underwent a 2nd operation to replace the Co and Cr alloy prosthesis in January 2004. One week after the 2nd operation, redness and swelling of her right knee developed, and suppurative drainage continued from the pin-hall of the wound. Although repeated bacterial and fungal cultures of pus were negative, she was given antibiotics. A 2-day closed patch test with a metal allergen from Torii Pharmaceutical Co. Ltd (Tokyo Japan) showed positive reactions to only Co and Cr in December 2004. She underwent a 3rd operation to remove the Co and Cr alloy prosthesis of her right knee in February 2005, and suppuration improved 2 months later. A diagnosis of Co-Cr alloy allergy mimicking suppurative arthritis was made. Patch testing is indispensable for patients with persistent inflammation after implantation of a prosthesis made of an alloy of Co and Cr and for preoperative patients for whom implantation of a prosthesis made of metals is planned.