Failure of a Medial Unicompartmental Knee Replacement due to Metal Allergy

Metal hypersensitivity is an uncommon complication of knee arthroplasty that can lead to significant functional impairment and aseptic prosthesis failure. We describe the case of a 65-yr-old female patient who presented with persistent pain, swelling, and instability 1 yr after medial unicompartmental knee arthroplasty (UKA). The patient had no history of trauma or fall. The initial clinical examination showed good range of movement in the knee joint and no signs of infection or inflammation. Initial radiographs did not reveal aseptic loosening of the implant. Inflammatory markers were normal and the patient was sent for a bone scintigraphy that revealed increased uptake of the femoral implant. Pain deteriorated during the proceeding weeks, and repeated radiographs revealed loosening and dislocation of the femoral implant. We performed a nickel lymphocyte proliferation skin allergy test that resulted in a positive reaction. Revision total knee arthroplasty was performed using an oxynium (zirconium metal alloy) implant with intraoperative tissue pathology and postoperative leukocyte transformation testing that confirmed metal hypersensitivity as the cause for aseptic implant failure. This case report demonstrates that clinical and laboratory signs suggesting metal hypersensitivity in knee arthroplasty can suggest early loosening and failure of the implant.