For radiosynovectomy , researchers have measured the retention time of yttrium-90 ( 90 Y) hydroxyapatite (particle size 1-10 μm) within the knee joint space and evaluated the treatment responses in knees with rheumatoid arthritis .

In rheumatoid arthritis, pain, swelling, and functional disorders of joints are often satisfactorily treated by oral anti-inflammatory or immunosuppressive drugs when symptoms are mild.

However, in chronic, persistent inflammation, additional local treatment must be used. Well-established local treatment options are surgical resection, intra-articular steroid application, and radiosynovectomy

many studies have described negative effects on articular cartilage metabolism and vitality. Furthermore, repeated intra-articular steroid applications often resulted in less time periods of effective pain relief.

For radiosynovectomy, β-emitting radiocolloids are used for intra-articular application. 90 And is presently considered to be a suitable radionuclide for the knee joint with rheumatoid arthritis because of its deep tissue penetration (mean = 3.6 mm, maximum = 11 mm).

A total of 25 patients (13 males and 12 females) with 40 rheumatoid knees and Stage I and II classified according to the American Rheumatoid Association were selected for the study. The age range was 45-60 years old with mean age of 49.9 years old.

These patients were mandatory adequate standard baseline pharmacotherapy with anti-inflammatory drug or intra-articular steroid application for at list 6 months before radiosynovectomy and failed in those.

Each patient was treated with 90 and hydroxyapatite 185 MBq (5 mCi) per joint for intra-articular therapy of the knee of which a particle size was 1-10 μm.

Knee joint puncture for radiosynovectomy has done following the rules of strict asepsis and intra-articular needle placement has been ensured by aspiration of joint fluid through the needle which is used to inject  90 Y-colloid. 

Treatment responses were evaluated as of clinical signs and symptoms at 6 and 12 months after injection.

Researchers defined "very good" as a result of the clinical practice of arthritis; "Good" implies a striking improvement of all clinical signs and symptoms; "Fair" implies improvement of some clinical abnormalities; and "none" implies to be the same as before the treatment.

The clinical improvements in rheumatoid arthritis of knee joint with steinbroker Stages I and II were increased as time goes by, the improvement ratio is in 72% at 6 th  months and 76% at 12 th  months after injection of 90 and 185 MBq (5 mCi ) per joint.