Treatment of pigmented villonodular synovitis of the knee with yttrium-90 silicate: prospective evaluations by arthroscopy, histology, and 99mTc pertechnetate uptake measurements.

The diffuse form of pigmented villonodular synovitis of eight knee joints of eight patients was treated by intra-articular injection of 185 MBq yttrium-90 silicate (90Y). Six patients had a recurrence of disease after one or two surgical synovectomies. After treatment with 90Y once or twice four knees showed clinical improvement with an accompanying decrease of the inflammatory activity as measured by the technetium-99m pertechnetate (99mTcO4-) uptake ratio and the severity of the diseased synovial tissue. Arthroscopy was performed before and six months after each 90Y treatment. The ratio of 99mTcO4- uptake in the inflamed compared with the normal knee joint correlated well with the macroscopical grading of pigmented villonodular synovitis. In all cases areas of persistent synovitis were found after the 90Y injection and this was confirmed both by histological examination and 99mTcO4- uptake measurements. Biopsy specimens taken from the diseased synovial areas showed histologically mostly less prominent and less numerous villi. The cartilage damage was slightly increased in only two cases. No radiological deterioration was found during follow up (mean 24 months, range 12-41). No complications of the radiosynoviortheses were noted.