Synovial metastasis: an unusual cause of pain after total knee arthroplasty.

There is only 1 previous report of synovial metastasis to a joint that has been replaced. A 73-year-old man presented for investigation of continuing pain after a left total knee arthroplasty with normal plain radiographs. Synovial biopsy revealed metastatic adenocarcinoma of colorectal type. A barium enema and flexible sigmoidoscopy showed a suspicious lesion at the rectosigmoid junction. The knee is the most frequently affected joint, and the lung is the most common primary site for synovial metastasis. This phenomenon should be considered in the differential diagnosis of continuing pain and effusion postarthroplasty.