Pulsed Radiofrequency

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Chapter 16 Pulsed Radiofrequency

Khalid Malik, Honorio T. Benzon

Chapter Overview

Chapter Synopsis: Radiofrequency (RF) techniques are used to ablate neural tissue in the treatment of painful conditions by delivering thermal lesions. This chapter focuses on a procedure known as pulsed RF (PRF), which sends pulses of electrical currents to an electrode tip to targeted nerve tissue. The pulsatile nature of the stimulation allows the tip to cool between pulses, keeping the electrode below 42° C, the temperature at which damage to surrounding tissue would occur. The targeted nociceptive tissue is thought to sustain damage from high-density electrical fields generated during the PRF, although the mechanism of destruction is not entirely understood. PRF has been used in a wide variety of both painful and nonpainful conditions. Notably, the technique has been applied at every spinal level of the dorsal root ganglia (DRG) and at many peripheral nerve sites. PRF is most commonly used to treat lumbar or cervical radicular pain. Although data from observational studies indicate that the procedure is quite effective for the treatment of radicular pain, two randomized controlled studies suggest only short-term analgesic benefits.

Important Points:

During PRF application, an attempt is made to maximize the delivery of RF currents while the thermal tissue injury is minimized by maintaining the tissue temperature below the neurodestructive range.

The RF currents are applied in a pulsatile manner so the heat can dissipate in between the RF pulses.

PRF is applied by placing an electrode in the vicinity of the target nociceptive structure; however, because the electrical currents extend radially from the electrode tip, juxtapositioning of the electrode tip parallel to the target nerve is considered unnecessary.

It is assumed that sustained high-density electrical fields generated during PRF application stress the biomolecules and cause cellular dysfunction and death of the target neural structure.

Standard PRF protocol constitutes RF currents applied for 20 msec at 2 Hz for a total duration of 120 seconds while the maximum electrode temperature is maintained below 42° C.

No noticeable side effects or complications have been attributed directly to PRF use.

Clinical Pearl: Due to the relative safety of PRF, its clinical use is widespread, and it has been applied to an array of structures including central nervous system ganglia, peripheral nerves, intervertebral discs, joints, and myofascial trigger points for the treatment of a range of pain syndromes.

Clinical Pitfall: Observational studies on this topic are abundant, and they almost universally support the PRF use. However, only a few controlled trials of PRF use are available, and they report its variable efficacy, which at best is short term.

Introduction and History

Radiofrequency (RF) currents have been used clinically to create predictable and quantifiable thermal lesions since the 1950s and have been used in the treatment of pain since the early 1970s.¹ During conventional RF (CRF) application for the treatment of pain, the RF currents are passed through an electrode that is placed in the vicinity of a nociceptive pathway. Consequently, the electrical energy imparted to the tissues immediately surrounding the active electrode tip creates a thermal lesion, likely interrupting the nociceptive impulses.² Because tissue temperatures above 45° C are known to be neurodestructive,³ tissue temperatures are characteristically raised to well above the neurodestructive range but below the point of gas formation—80° C to 90° C. Although selective destruction of unmyelinated C and A-δ fibers by CRF thermal lesioning has been suggested,⁴ further studies showed indiscriminate destruction of all nerve fiber types during thermal CRF lesioning.⁵ Because of the possible risk of injury to the motor nerve fibers, local neuritis, loss of sensation, and deafferentation pain, the clinical use of CRF has generally been limited to facet denervation.⁶ Observation that low temperature non–tissue-destructive CRF application had results similar to high temperature tissue-destructive CRF generated immense interest. It was theorized that electrical currents rather than temperature determined the outcomes of CRF application.⁷ During pulsed RF (PRF), an attempt is made to maximize the delivery of electrical currents to the tissues by using higher voltage RF currents, and the risk of thermal tissue injury is minimized by maintaining the tissue temperatures below the neurodestructive range. These contradictory goals are achieved by applying the RF currents in a pulsatile manner to allow the heat to dissipate in between the RF pulses.⁸

Mechanism of Effect

Sluijter et al ⁸ in their first description of PRF use described its possible mechanism of action. These authors assumed that by maintaining the electrode temperatures below the thermal destructive range that thermal tissue injury was obviated and the sustained high-density electrical fields that were generated stressed the biomolecules and caused cellular dysfunction and death. However, later investigators observed the slow response time of the temperature-measuring devices used during PRF application and concluded that the generation of brief high-temperature spikes could not be excluded, suggesting a combined role of electrical and thermal tissue injury.^9,¹⁰ In laboratory studies, evidence of neuronal activation,^11,¹² cellular stress,¹³

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