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Radiosynoviorthesis (RSO) – Treatment & Effects

Radiosynoviorthesis (RSO) is a minimally invasive nuclear medicine procedure used to treat inflamed joint linings, such as in rheumatoid arthritis or osteoarthritis.

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Things worth knowing about "Radiosynoviorthesis"

Radiosynoviorthesis (RSO) is a minimally invasive nuclear medicine procedure used to treat inflamed joint linings, such as in rheumatoid arthritis or osteoarthritis.

What is Radiosynoviorthesis?

Radiosynoviorthesis (RSO), also referred to as radiation synovectomy, is a nuclear medicine treatment in which a radioactive substance is injected directly into a diseased joint. The goal is to selectively destroy the inflamed synovial membrane (synovium), thereby permanently reducing pain and inflammation. The procedure is minimally invasive and is performed on an outpatient basis.

Indications

RSO is typically recommended when conservative treatments such as corticosteroid injections or anti-inflammatory medications have not provided sufficient relief. Common indications include:

Rheumatoid arthritis – chronic inflammatory joint disease
Osteoarthritis with accompanying synovitis (inflammation of the synovial membrane)
Psoriatic arthritis – joint inflammation associated with psoriasis
Reactive arthritis – joint inflammation triggered by infection
Haemophilic arthropathy – joint damage due to repeated bleeding in haemophilia
Pigmented villonodular synovitis (PVNS) – a rare condition affecting the joint lining

Mechanism of Action

During RSO, a radiopharmaceutical – a radioactive compound – is injected in liquid form directly into the joint space. The inflamed synovial cells absorb this substance, and the emitted beta radiation selectively damages the overgrown synovial tissue, inducing scarring (fibrosis). This process permanently reduces inflammatory activity within the joint.

Different radiopharmaceuticals are used depending on the size of the joint:

Yttrium-90 – for large joints such as the knee
Rhenium-186 – for medium-sized joints such as the shoulder, hip, or ankle
Erbium-169 – for small joints such as finger or toe joints

Procedure

RSO is typically performed on an outpatient basis in a nuclear medicine department or clinic. The procedure involves the following steps:

Disinfection and, if necessary, local anaesthesia of the joint area
Ultrasound- or fluoroscopy-guided injection of the radiopharmaceutical into the joint cavity
Co-injection of a corticosteroid preparation to reduce any immediate inflammatory response
Immobilisation of the treated joint for 48 hours using a splint or bandage

After the procedure, the joint should be kept at rest for at least 48 hours to maximise the local retention of the radiopharmaceutical and to minimise radiation exposure to surrounding tissue and other individuals.

Efficacy and Outcomes

Clinical studies indicate that RSO leads to a significant improvement in symptoms in approximately 60–80% of treated patients. The full therapeutic effect may take several weeks to develop, as tissue remodelling requires time. In some cases, a second treatment may be considered after 6 months if the initial response is insufficient.

Side Effects and Risks

RSO is considered a very safe procedure with a low side effect profile. Possible adverse effects include:

Temporary swelling or increased pain in the treated joint (radiation reaction)
Very rare injection-related inflammatory reactions
Minimal systemic radiation exposure, which is considered clinically negligible

The total radiation dose to the body is very low when the procedure is performed correctly. Nevertheless, RSO is contraindicated in pregnant women, breastfeeding mothers, and patients under 20 years of age.

Advantages Over Surgical Alternatives

Compared to surgical synovectomy (operative removal of the synovial membrane), RSO offers several advantages:

Minimally invasive and performed on an outpatient basis
No general anaesthesia required
Short recovery time
Lower risk of complications

A potential disadvantage is that the therapeutic effect is not immediate and requires several weeks of patience before the outcome can be assessed.

References

Schneider P. et al. – Radiosynoviorthesis: Guidelines of the German Society of Nuclear Medicine, DGN, 2020.
Jahangier ZN et al. – The effect of radiation synovectomy in patients with persistent arthritis: a systematic review. Rheumatology (Oxford), 2006; 45(5):539–547.
European Association of Nuclear Medicine (EANM) – EANM guidelines for radiosynoviorthesis, 2003. Available at: www.eanm.org

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