Radiofrequency ablation (RFA) is a technique used to treat a variety of conditions including cancers and cardiac arrhythmias, and has become increasingly used in decreasing chronic pain in people with musculoskeletal disorders. When an area of the body becomes irritated and inflamed due to a condition such as osteoarthritis, a pain signal is transmitted to the brain through the nerve which supplies the affected area. If this signal can become disrupted by destroying the transmitting nerve, some of the pain perceived from the affected area can be decreased. Commonly targeted nerves include the medial branches of the dorsal rami which innervated the facet joints in the spine, the S1-3 lateral nerves which innervate the SI joint and the geniculate nerves, which provide innervation to the knee. These nerves can be targeted under ultrasound or x-ray guidance, and destroyed by a process called radiofrequency ablation.
Radiofrequency ablation uses an alternating electrical current to deliver energy in the form of heat to a probe tip. Damage to the tissue first occurs to an area just beyond the tip through resistance heating. A difference in impedance between this small area of tissue and probe tip causes the small area of tissue to produce conductive heat. This transfers heat to adjacent tissue and expands the area of damaged tissue. The temperature from the conductive heat is sensed by a device within the probe and allows the temperature at the tip to be monitored. Maximum tissue destruction occurs at temperatures between 60C and 70C. However, when the temperature exceeds 100C (212F) steam and coagulation occur at the probe tip. To prevent this, most thermal radiofrequency devices automatically shut off when the probe reaches this temperature. If the device shuts off prematurely, however, this can result in an ineffective lesion. To keep the probe at an ideal temperature, a probe with a cooled tip may be used. In these cooled radiofrequency ablation systems saline is pumped through the probe tip, turns around within the tip and then returns to the pump. This mechanism allows for the ability to lengthen ablation times and to allow for larger lesions to be formed. As the nerves are not usually visualized directly when nerve ablation procedures are performed, a larger lesion theoretically would have a better chance at contacting and destroying more of the pain-transmitting nervous tissue.
Commonly targeted nerves for radiofrequency ablation are the medial branches of the dorsal rami which innervate the facet joints in the spine and contribute to some types of back pain. There have been several trials, including a recent randomized controlled trial, which have directly compared cooled and thermal RFA. In these trials there was no statistically significant difference in pain reduction between the two types of RFA.
Another commonly ablated nerve system is the geniculate nerves which provide sensation to the knee and transmit the pain signals from the knee joint. Thermal RFA has been demonstrated lead to greater improvement in pain relief and function compared to sham RFA and also to decrease pain when compared to non-interventional therapy. The first study to employ cooled RFA was by Davis et al in 2018, and demonstrated improved pain relief and function when compared to intra-articular steroid injection. Based on the current literature, both thermal and cooled RFA are effective in patients who respond to lidocaine blocks of the geniculate nerves. However, more data are needed to determine if cooled RFA is more effective than thermal RFA in controlling pain and improving function.
Both cooled and thermal radiofrequency ablation of the nerves which innervate the sacroiliac (SI) joint have been shown to be effective in reducing pain in patients with SI joint pain for up to a year. Cooled RFA has been compared directly to thermal RFA, in 2003 Cheng et al compared 30 patients who received thermal RFA and 58 who received cooled RFA. Both cooled and traditional RFA provided more than 50% pain reduction for 3-6 months in the majority of patients. However, there was no difference between cooled and thermal RFA in the duration of pain even after adjusting for potentially confounding variables.
Cooled and thermal radiofrequency ablation procedures are used to help control pain. They work by destroying nerve tissue which transmits pain signals from painful areas within the body. They are commonly used to help control certain types of back pain, SI joint pain and knee pain. Cooled radiofrequency ablation uses a fluid-cooled probe and allows for the formation of larger lesions at the probe tip. This increases the chance that the procedure destroys the target nerve tissue, and theoretically should allow for more successful procedures and decreased pain. Currently, both cooled and thermal radiofrequency ablation techniques have been shown to decrease pain and increase function in most people who respond to initial nerve blocks. Data so far suggests that there are not significant differences in pain reduction between cooled and thermal RFA. However, there is not yet good high-quality data comparing the two types directly with respect to differences in patient pain or function.
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