History

The first known use of thermocoagulation for the treatment of chronic pain was in 1931, with successful ablation of the gasserian ganglion for trigeminal neuralgia by Martin Kirschner. A direct current of 350 mA was delivered through a 10-mm uninsulated tip, which produced a lesion of unpredictable size. However, the use of thermal energy for the destruction of tissue may be traced back to even earlier, in the mid-1800s, when direct current was used to create a lesion in an animal brain. This is when preliminary thoughts of quantifying lesion size based on current and time came about.

The use of high-frequency electric current was found to produce lesions of predictable size and was named “radiofrequency” current because the same frequencies of 300 to 500 kHz were also used in radio transmitters. In the late 1950s, the first commercial radiofrequency (RF) lesion generator was developed by Cosman and Aronow. ^, During stereotactic brain surgery in 1960, using the refined RF lesioning, Mundlinger et al. studied controlled dosages of RF and found that temperature monitoring was the most important factor in obtaining a standardized lesion size. The first use of RF lesioning for pain management occurred in 1965, when Rosomoff performed a percutaneous lateral cordotomy for unilateral pain in cancer patients.

In 1968, Letcher and Goldring demonstrated that RF lesions block the action potentials of small nociceptive fibers in cats, preferentially sparing motor and proprioceptive fibers, which denoted the initial understanding of nerve fiber selectivity by thermocoagulation and ultimately introduced the concept of RF lesioning for therapeutic purposes. In 1974, Sweet and Wepsic noted that touch was preserved in some or all of a zone deemed analgesic while performing percutaneous retrogasserian thermal rhizotomy, concluding that large, heavily myelinated fibers were more resistant to heating than small nerve fibers.

In 1975, Shealy et al. performed the first RF lesioning for spinal pain. The medial branches of the facet joints were ablated using a 14-gauge electrode inserted through a 12-gauge guide needle, which is fairly large compared to the 18- or 20-gauge cannula with a 10 mm active tip used presently. It was thought that mechanical lesions along with thermal lesions were produced due to the large size. Some of the most common procedures performed today by pain management specialists are medial branch blocks and RF ablation (RFA).

Another use for RF lesioning for spinal pain was introduced by Uemetsu, who first performed the procedure for dorsal root ganglion (DRG) lesioning, using the same electrode that was used by Shealy for medial branch lesioning. However, combining the tip temperature of 75°C with the large electrode diameter produced sizeable lesions that resulted in deafferentation pain when used for spinal pain, and the utility for RF lesioning became limited to percutaneous cordotomy and gasserian ganglion ablation.

In addition, contradictory findings were shown after the work of Sweet and Wepsic in 1974. In 1977, histologic studies of the sciatic nerve in cats showed indiscriminate destruction of Aδ and C fibers, along with motor and proprioceptive nerves. This was supported by Smith et al. in 1981, who demonstrated lack of specificity at RF lesioning temperatures of 45°C, 55°C, 65°C, and 75°C in dogs. Due to these findings, RF lesioning fell out of favor for the time being.

It wasn’t until the 1980s that the use of RFA for spinal pain was reintroduced due to crucial modifications made to the electrode. The electrode was made to be significantly smaller and capable of temperature monitoring, which eliminated the pan-destructive mechanical and thermal lesioning created by larger-diameter electrodes that were previously used. The Sluijter Mehta Kit (SMK) system consisted of a 22-gauge disposable cannula with a thermo-coupled probe included for temperature measurement, resulting in less risk and discomfort during procedures. Due to this novel electrode system, RFA for medial branches and adjacent to the dorsal root ganglion became a therapeutic option in the field of pain management. With the combination of small-diameter RF needles and the use of enhanced imaging under fluoroscopy for precise placement of needles, a current passed through the electrode could reliably reproduce the patient’s concordant pain, and a thermal lesion could then target specific neural structures. After extensive studies were performed to investigate the optimal time and temperature needed for neurolysis, the standard of generating a lesion at 80°C for 60 to 90 seconds was established.

In the 1980s and 1990s, more evidence became available regarding sympathetically mediated or maintained pain syndromes, which became an area of interest regarding RF lesioning. In 1984, Wilkinson developed an effective treatment for central hyperhidrosis using RF thoracic sympathectomy at the T2–3 and, at times, T4 levels, followed by the development of the percutaneous RF lumbar sympathectomy. Sluijter developed the cervicothoracic RF sympatholysis for treatment of sympathetically mediated or maintained pain syndromes of the face, head, neck, shoulder, and upper extremity. The use of RF lesioning to produce dorsal root entry zone (DREZ) lesions for treatment of deafferentation pain such as brachial plexus and conus medullaris avulsions, phantom pain syndromes, and postherpetic neuralgias was also introduced during this time frame.

Neuroanatomic studies have demonstrated that the intervertebral disk is highly innervated, motivating Sluijter to introduce RF lesioning for the treatment of discogenic pain in 1996. It is thought that annular tears induce discogenic pain, and nociceptive fibers in the posterior annulus (thought to be derived from the sinuvertebral and sympathetic nerves) could be effectively ablated through intradiscal RF lesioning.

Over the years, the simplicity of using heat to disrupt nociceptive transmission was questioned. This concept suggests that the thermal lesion must be made in between the nociceptive stimulus and the central nervous system, but RF lesioning can be successfully utilized in other situations. In the treatment of acute radiculitis due to disc herniation, the electrode is placed distally to the nociceptive focus, and lesioning adjacent to the DRG induces only transient sensory loss that is heat related, but the pain relief may be of much longer duration.

Pulsed-dose RF lesioning, developed in 1996, was intended to be a minimally invasive pain relief modality that did not cause neurodestruction. The mechanism of neuromodulation remains to be fully elucidated, but it is thought that high current in the electromagnetic field may reversibly disrupt the sodium or calcium pump in the dorsal root ganglion, rendering small nociceptive fibers less capable of pain transmission while sparing larger fibers that are protected by their myelin sheath. In addition, maintaining the electrode temperature at 42°C ensures that neural structures are not damaged. Pulsed-dose RF lesioning is not used for neurotomy of the medial branches of the dorsal rami, as the technique has not been shown to provide a consistent lesion. Two of the potential side effects of conventional RFA are painful cutaneous dysesthesias and increased pain due to neuritis, which may be mitigated by pulsed RF lesioning.

Cooled RF lesioning was developed around the same time as pulsed RF lesioning. When traditional RF electrodes are not placed properly in parallel to the medial branch nerve, there is a risk of not capturing the nerve within the radius of the thermal lesion. Cooled RF technology creates a spherical, forward-projecting lesion, ^, which provides a theoretical technical advantage in capturing a target medial branch nerve, as the RF probe can be positioned at a range of possible angles and still capture the target neural structure. Cooled RF has shown effectiveness for sacroiliac joint pain, knee pain due to osteoarthritis (OA), ^, and facet-mediated pain.

The start of the 21st century brought about additional uses for RFA. Lateral branch blocks and sensory stimulation-guided neurotomy were developed for the treatment of sacroiliac joint pain. ^, Radiofrequency ablation of the geniculate nerves for knee osteoarthritis was introduced in 2010 and remains a commonly performed procedure today.

Radiofrequency lesioning for the treatment of persistent spinal and peripheral joint pain has increased substantially over the past few decades, due to its minimal invasiveness and effectiveness in properly selected patients when used along with a multidisciplinary approach for the treatment of chronic pain.