BACKGROUND AND EVOLUTION OF RADIOFREQUENCY TREATMENT
Radiofrequency ablation (RFA) has an established and expanding role in the treatment of a myriad of pain conditions. As early as the 1930s, the application of electric current for neural ablation was reported in the medical literature. Clinicians initially used large (12–14 gauge) electrodes emitting direct current, which risked mechanical injury and produced unpredictable lesions.1 However, investigators soon discovered that alternating current in the radiofrequency (RF) range between 300 and 500 KHz created more predictable lesions.2,3 In the early 1950s, the first commercial RF lesion generator became available through the collaboration between electrical engineer Bernard Cosman and neurosurgeon Thomas Sweet at the Massachusetts General Hospital. In 1975, RFA was first described in the literature for the treatment of back pain.1,4 Over the subsequent decades, RFA has become a widespread and effective treatment to create significant and sustained pain relief. Current and expanding clinical applications of RFA include facial; cervical, thoracic, and lumbar facet; spinal radicular; sacroiliac joint (SIJ); lumbar discogenic; peripheral nerve; intraarticular joint; and sympathetically mediated pain. The bulk of clinical data involves conventional RFA; however, over the past decade, modified forms of RF treatments have emerged. Today four forms of RFA predominate in clinical use: conventional (i.e. continuous) RFA (CRF), pulsed RFA (PRF), water-cooled RFA (WCRF), and bipolar RFA (BRF) (Fig. 91-1):
A 22-gauge, 10-cm SMK radiofrequency cannula with a 5-mm active tip is immersed in egg white, and conventional radiofrequency ablation is applied at 80°C for 90 seconds. The radial size of the lesion is maximal near the midportion of the active tip. Thus, for optimal application of conventional radiofrequency ablation treatment, the shaft of the needle's active tip is optimally placed adjacent to the target. The size of the lesion is near maximal by 60 seconds of treatment.118 Notably, however, egg white immersion setups, although useful for illustrative purposes, can also underestimate heating at the distal end of the electrode because fluid convection causes heated egg white to flow upward. (Used with permission from and image courtesy of Dr. James Rathmell from Atlas of Image-Guided Intervention in Regional Anesthesia and Pain Medicine.5)
Conventional RFA (CRF): RF current is administered continuously for 60 to 150 seconds at a specific temperature, usually 80°C.
Pulsed RFA (PRF): Intermittent brief pulse (20 ms/pulse) of RF current is administered every half second. Lesion temperatures are often maintained at 42°C, which is below the thermocoagulation threshold.
Water-cooled RFA (WCRF): Continuous RF current that involves a specialized cannula needle that has cool water circulating within the electrode to prevent surrounding tissue from reaching excessive temperatures. It permits larger lesions to be created, which can also extend distal to the electrode tip.
Bipolar RFA (BRF): Involves two electrode tips placed side by side so that current density and electric fields ...