Severe persistent synovitis after cobalt-chromium total knee arthroplasty requiring revision.

Implant-related hypersensitivity is a well-established cause of failure after total hip arthroplasty but is a rare complication after total knee arthroplasty (TKA). It remains a relatively unpredictable and poorly understood cause of implant-related failure. This article describes 5 patients (6 knees) who presented with persistent pain and hypertrophic synovitis after TKA using a cobalt-chromium component. Extensive perioperative workup, including white blood cell count, erythrocyte sedimentation rate, C-reactive protein, joint aspiration, and intraoperative cultures, ruled out infection as a cause of the symptoms. All knees demonstrated appropriate ligamentous balance and were well aligned, with all components noted to be well fixed at revision. In all patients, the clinical condition improved dramatically after revision to zirconium femoral and titanium metal-backed tibial components. Pain and functional outcome scores improved in all patients. Intraoperative histopathology revealed a thickened synovium with either a predominantly lymphocytic or histiocytic monocellular response. Final pathology confirmed that no infection was present in any patient. The goal of TKA is to produce a well-performing, pain-free joint. When patients present with recurrent pain and synovitis after TKA, infection must be excluded. When infection and instability have been excluded, metal hypersensitivity should be considered as a cause of primary TKA failure. In these patients, revision to a zirconium femoral component can provide predictable and effective clinical improvement.