The term radiosynoviorthesis (RSO) refers to a nuclear medicine treatment method which has been in use for several years in the local treatment of chronic inflammatory joint diseases. Etymologically, the term radiosynoviorthesis means the restoration of the synovial (joint) membrane using radiation.

Chronic inflammatory joint diseases are long-term inflammations of the synovial membrane, which becomes thickened and often overgrown with protrusions. The inflammation can be caused or triggered by a variety of factors. If inflammation persists long term, it can cause damage to further important structures within the joint, such as cartilage and bone (secondary arthrosis).

Any joints at extremities can be treated using RSO. It is indicated in cases of any rheumatic disease (usually following 6 months of basic treatment with insufficient effect), osteoarthritis and chronic synovitis following joint replacement with repeated occurrence of articular effusion.

Usually, 3 phase skeletal scintigraphy or an MRI scan with a contrast agent is required for diagnosis and treatment planning.

The skin is thoroughly disinfected, the area locally anaesthetised and sterile surroundings assured before the joint is punctured. A small amount of contrast agent is injected and used to ensure and document correct positioning of the needle. A mildly radioactive substance is then injected. Different joints require different radioisotopes and different doses.

Perfusion scintigraphy is then carried out to document the substance’s spread into the joint.

Finally a sterile bandage and a splint are applied.

The treated joint should not be moved for 48 hours following radiosynoviorthesis. This is why a splint is applied. When leg joints are treated, mobility aids will also be required. RSO usually only takes full effect after a significant delay (usually 6–12 weeks, in some cases up to 6 months). Repeat treatment is rarely necessary. An aftercare examination should take place after approx. 6 months.

The radioisotopes used emit a type of radiation known as beta radiation over a short or very short range. Their effect is targeted to the joint membrane but without damaging the healthy tissue, e.g. cartilage or bone. The radiation will not affect anyone around you.