Radiosynoviorthesis (RSO) is used for the treatment of inflammatory joint diseases. However, there are no long-term results published comparing it to conservative therapy. Therefore, the aim of this prospective observational study was to evaluate response rates after radionuclide therapy in patients suffering from knee osteoarthritis over a time period of 10 years.
Radionuclide therapy with intra-articular administration of colloidal 
In patients with early-stage disease, an excellent/good response with respect to pain, joint mobility, and function was observed in 82.5% for 1 year and in 73.7% for 8 years after therapy. Responses declined to 50% at 10 years post treatment. In grade III patients, an excellent/good response was observed in 45.9%; a decline to 41.2% was observed in the first 8 years. In this group, the number of patients available for follow-up after 9 and 10 years dropped significantly from 51 patients after 8 years to only 30 patients after 9 years, and to nine patients after 10 years. As a result, these response rates were not appraisable.
Long-term results of radiosynoviorthesis in knee osteoarthritis are excellent/good in many patients. The response rate depends on Kellgren-Lawrence stages, and early-stage radionuclide therapy for osteoarthritis is suggested.