Knee RFA to treat chronic pain from OA

Osteoarthritis (also known as OA) is the most common type of arthritis and one of the most common causes of knee pain; affecting more than 1.3 million Australians..

Knee Osteoarthritis

Chronic knee pain from osteoarthritis (OA) affects at least 500 000 patients in Australia. The lifetime risk of developing knee OA is approximately 14%. There are 65 000 total knee replacements performed in 2018 and the number is rising rapidly due to the ageing population and obesity epidemic. OA is estimated to cost Australians 3.75 billion (2012 data). Knee joint replacement surgery is effective in many patients with severe OA, however 10-30% of patients report significant pain or functional impediment post replacement.

The conservative management of knee OA includes – weight loss, exercise, physiotherapy, analgesic medication (1). Additional options may include injectable medications including corticosteroid(CSI) and hyaluronic acid (HLA)eg Synvisc, Durolane, Euflexxa. Limited evidence in a 2019 review suggests CSI may accelerate OAdue to a chondrotoxic effect (2). HLA is considered to be a safer option as there is no chondrotoxicity.

RFA Genicular Nerves

There is a place in the knee OA treatment algorithm for Radiofrequency Ablation of the genicular nerves (3). The treatment can be considered for patients who have ongoing pain despite standard medication treatment and exercise/weight loss. RFA has been used to treat spinal facet joint pain, sacroiliac pain, chronic plantar fascia pain, Morton’s neuroma and refractory shoulder pain. Extending RFA to treat knee OA pain is a logical step given the relative ease by which the genicular nerves can be treated under imaging guidance.

RF Procedure

An image guided RFA of genicular nerves is performed as a day-procedure in our radiology clinic under CT guidance and with local anaesthetic only. The radiofrequency cannula and electrodes are positioned at the sites of the superior medial/lateral and inferior medial genicular nerves. Radiofrequency current is then emitted from the tip of the electrode causing a small volume of tissue around the nerve to be heated and blocking pain signals from the specific genicular nerve branches. The current is applied for 2-4 minutes and then the cannula and electrode are removed at the end of the treatment.

The procedure is very well tolerated with minimal to mild discomfort after the local anaesthetic has been administered. There is more discomfort when continuous thermal RF (70-90 deg C) is utilisedas opposed to pulsed RF (42 deg C). The decision to select which energy level is made by the performing radiologist and/or referring practitioner.

Post procedure

The first 48 hours require relative rest with minimal walking and activities. Most patients can resume normal activities after 48 hours including return to work and gentle exercise.

Risks:

Whilst the procedure is generally very well tolerated, there are risks involved including bleeding, infection, and increased knee pain from heat injury. These complications are rarely seen from the procedure.

Efficacy

The treatment is generally effective for most patients with chronic knee pain from osteoarthritis. The degree of pain reduction is estimated to be 60-80% as the 3 treated genicular nerves supply this proportion of pain signals from the knee. The duration of effect is 6-18 months. The procedure can be repeated after 6 months if effective initially. The treatment has the potential to delay TKR for approx. 5-10 years in selected patients.

Which patients are best suited for Knee RF?

• Chronic knee pain >6 months
• Moderate to severe OA (Grade 3-4) on XR
• Failure to respond to basic OA medical management
• Unsuitable (or unwilling) to undergo TKR
• Prior TKR with ongoing pain

What imaging is needed?

• XR knees including weightbearing within 12 months
• MRI or CT are optional (to exclude meniscal/ligament pathology)

How do I refer a patient to have Knee RFA?

• Referral letter to Dr Hamlin (valid 12 months)
• Request form – “CT guided Knee RFA” (valid 7 days)
• Fax copy of XR/MRI results
• The waiting time for procedures is approx. 7 days currently

References

• Clinical standards of care 2018. Osteoarthritis of the knee – the case for improvement.
• Kijowski R. Radiology Oct 2019. Risks and Benefits of IA CSI for treatment of OA: What radiologists and patients need to know.
• Zhang H. J Int Med Res, 2021 April 49(4). Efficacy and safety of RFA for treatment of knee OA: a meta-analysis of RCTs.

Appendix

AOA.org.au – 2018 – joint replacements;