Pulsed Radiofrequency, Water-Cooled Radiofrequency, and Cryoneurolysis

Sluijter et al.8 assumed that, because the tissue temperature was kept below the thermal destructive range, thermal tissue injury was avoided. By using mathematical calculations, they further showed that the high-density electrical currents generated at the electrode tip stressed the cellular membranes and biomolecules and caused altered cell function, leading to cell injury. Later investigators, however, suggested a combined role of electrical and thermal tissue injury from PRF application.9,10 These authors also ascertained that the slow response time of the temperature-measuring devices used during PRF could not reliably exclude the possibility of brief high-temperature spikes and the likelihood of thermal tissue injury. Although some laboratory studies showed evidence of neuronal activation,11,12 cellular stress,13 and cellular substructure damage9 after PRF application, others showed that the observed PRF effects were predominantly a function of set temperature,14,15 and thus undermined the role of the electrical currents in causing tissue injury. Thus, despite the several claims of its clinical efficacy, the exact mechanism of the clinical effects of PRF hitherto remains unclear, and currently no evidence of the interruption of the nociceptive pathway in response to PRF application exists. Similarly to CRF, PRF is applied via an electrode placed in the vicinity of the target nociceptive structure. However, unlike CRF, juxtapositioning of the electrode parallel to the target nerve is deemed unnecessary, as the electrical currents, and not the thermal lesion, are considered the source of neuronal dysfunction. During typical PRF application, the RF currents are applied for 20 milliseconds, at 2 Hz, for a total duration of 120 seconds. Therefore, for most of the lesion duration—480–500 milliseconds—no RF currents are applied. The current voltage is controlled in a manner that the maximum electrode temperature achieved remains below 42° C.8 Variations from this standard PRF protocol have been infrequent, with the exception of longer lesion duration: PRF has been applied for 4, 8, and 20 minutes in some clinical studies.16