Radiographic detection of metal-induced synovitis as a complication of arthroplasty of the knee.

Radiographs of eighteen patients who had had a diagnosis of metal-induced synovitis subsequent to a knee-replacement arthroplasty were retrospectively reviewed. The presence of a dense line outlining a portion of the capsule or articular surface of the knee joint (the so-called metal-line sign) was noted in association with wear in eleven patients. In the nine patients who had a positive sign and also had specimens available for histological examination, there was dense deposition of metal particles, whereas in the six patients who did not have a metal-line sign and had specimens available for histological examination, five had only a slight amount of metal in the synovial tissue and one, a moderate amount. The presence of the metal-line sign was associated with metal-induced synovitis in eleven of the eighteen patients. The sign should be useful in helping to make this diagnosis preoperatively in many patients.