Short-Term Effect of Radiofrequency on Osteoarthritic Knee Pain
This study was an effort to find alternative treatments for painful knee osteoarthritis. The authors used radiofrequency (heat treatment) to kill three small branches of the sensory nerves to the knee (genicular nerves). The procedure is called a radiofrequency neurotomy.
The 38 patients in the study had severe knee pain from osteoarthritis. The painful symptoms had been present for at least three months, which makes it chronic pain by definition. They had all tried (and failed) to get relief with conservative care.
Everyone in the study did get relief from a diagnostic nerve block (injection of numbing agent into or near the nerve). Nerve blocks are used to confirm that nerve irritation is the problem and source of pain. But a nerve block only provides temporary effects. Once the pain came back, then this study with radiofrequency ablation was done to end painful symptoms permanently.
Half the patients received a true radiofrequency treatment to three branches of the genicular nerve. The surgeon creates a tiny tunnel through the skin and soft tissues down to the bone. Fluoroscopy (real-time X-rays) and sensory stimulation were used to make sure the surgeon was close enough to the nerve to make accurate contact.
After the nerve was located then a radiofrequency probe was passed through the tunnel to the nerve. The tip of the electrode was heated up to 70 degrees Celsius (about 160 degree Fahrenheit) for 90 seconds. This ensures that the nerve is destroyed and no further pain transmission can get through.
Cutting the nerve supply to the joint is meant to reduce pain and thereby restore joint motion and function. The other half (control group) got the same procedure but without a true neurotomy being done. The radiofrequency probe was advanced through the skin to the nerve but no heat was applied to the area.
The treatment was considered a success if the patient got at least 50 per cent improvement in pain for more than a 24-hour period. Anything less than those criteria were considered a failed treatment. Additionally, before and after (at one, four, and 12 weeks after the procedure) measurements of pain and function were recorded.
The results showed a significant improvement in pain one week after the procedure for both groups. But only the radiofrequency (RF) group maintained pain relief and improved function at the rest of the follow-up appointments. Patients in the RF group were much more satisfied with their treatment results when compared with the control group.
The authors suggest that radiofrequency treatment for painful knee osteoarthritis is a possible treatment choice. It is safe and effective. But because it is an invasive procedure, other conservative approaches should be tried first. A diagnostic nerve block should also be done before using radiofrequency ablation.
There are times when the RF treatment is not successful. This is most likely because the target nerves vary in their anatomic location. And sometimes there are extra branches that still supply the joint with nerve impulses.
Pain is relieved only if and when all branches of the sensory nerves to the knee are found and destroyed. If the first procedure doesn't completely eliminate the pain, neurotomy can be repeated a second and even third time.
Further studies are needed to see how patients fare months to years later. Does radiofrequency ablation speed up osteoarthritic changes? Does it slow down degenerative changes? Are there adverse effects that only become apparent much later after the procedure? More evidence is needed before final conclusions and recommendations can be made.
Woo-Jong Choi, et al. Radiofrequency Treatment Relieves Chronic Knee Osteoarthritis Pain: A Double-Blind Randomized Controlled Trial. In PAIN. March 2011. Vol. 152. No. 3. Pp. 481-487.