Recurrent villonodular synovitis of the knee. Successful treatment with yttrium-90.

A 40-year-old woman with recurrent pigmented villonodular synovitis of the knee was treated with Yttrium-90 radiocolloid. The advantages of Yttrium-90 include effectiveness, low cost, simplicity, and low morbidity. The radiophysical properties of Yttrium-90 that make it a useful therapeutic agent are short half-life, pure beta emission and good penetration of the soft tissues. Side effects are few, predictable, and for the most part, avoidable. Radionecrosis of soft tissue, needle tract pigmentation, injection site tenderness, pyrexia, and lymphocyte chromosomal abnormalities have been reported. The indications for intra-articular radiocolloid therapy are the same as for surgical synovectomy, except that it is reserved for patients older than 35 years of age. The pathologic events following Yttrium-90 therapy in experimental animals show coagulation necrosis of the synovium, followed by an intense inflammatory reaction, leading ultimately to fibrosis. Yttrium-90 is a useful adjuvant in the treatment of recurrent pigmented villonodular synovitis.