Metallosis after total knee replacement.

Abstract

: swelli and loss of function 10 years after right total knee replacement using a cemented bicondylar implant with a metal-backed patellar component. Radiographs showed radiodense material outlining a grossly distended knee capsule (Fig. 1A). CT showed the radiodense material to contain metal (Fig. IB). At surgery, the joint capsule was filled with dark fluid. Metallic debris filled the joint and the synovium was grossly blackened and hypertrophic. The patellar polyethylene was worn through, exposing the underlying metal back to abrasion against the femoral component. but the tibial polyethylene was intact. Synovectomy and patellectomy were performed. The excised soft tissues consisted of metalstained fibrotic synovium with papillary hyperplasia (Fig. 1C). Microscopy showed polyethylene fragments eliciting giant cell foreign body reaction and granular black metal particles filling plump histiocytes (Fig. lD). The final pathologic diagnosis was metallosis (metal synovitis). Metallosis is a complication of total joint replacement caused by abrasion of metal components, typically after failure of interposed polyethylene-bearing surfaces. In one series I 11’ metallosis was present in seven of 30 patients with total knee replacements using metal-backed patellar components. Microscopic particles abraded from polyethylene surfaces are known to provoke a giant cell foreign body reaction that results in osteolysis and implant loosening, but a major role for metal debris-containing histiocytes in this process has also been suggested [2]. Metal and polyethylene particles may be carned away from joint replacements by the lymphatic system [3] with uncertain systemic effects. The characteristic radiographic finding of metallosis after total knee replacement is a radiodensity outlining the suprapatellar recess of the joint capsule caused by the presence of embedded metal particles 14]Arthrocentesis produces a thick dark gray or black fluid. Metallosis is treated by synovectomy and