Anand Thakur C. MD1, Serdar Erdine MD, FIPP2, and Peter S. Staats MD, MBA3 1 Clinton Charter Township, MI, USA Radiofrequency (RF) lesioning is one of the most effective techniques used to selectively destroy the nerves in the treatment of chronic pain. However, the risk of this approach cannot be underestimated and should be considered after more conservative options have failed. Moreover, the clinician performing the lesioning must be proficient in the technique and aware of the many possible complications. In the absence of caution, these techniques can be extremely dangerous. There are a variety of complications that can occur with ablating nerves using RF or thermal energy. A knowledge of physics, anatomy, and pathophysiology is necessary to minimize these risks. While heat, thermal energy and chemical techniques have most certainly been used in the management of pain for thousands of years, the use of electrical techniques has been around for close to 100 years. In 1931, Kirschner successfully used thermocoagulation of the gasserian ganglion to treat a patient with trigeminal neuralgia. While other techniques have been used for destroying nerves including alcohol, this was the first known use of RF lesioning for the treatment of chronic pain [1]. Later, Sweet and Mark demonstrated that use of a very high frequency current (in the RF range) has decisive advantages over direct current lesion procedures [2]. The earlier direct current approach utilized a lower current with a 10-mm uninsulated needle, without temperature monitoring, creating a lesion with great variability in size. By increasing the frequency to 300–500 khz and controlling for temperature, the lesion size became more predictable. Since these frequencies were also used in radios it became known as “radio frequency lesioning”. Later, Bernard J. Cosman made parallel pioneering contributions to the design and engineering of RF lesion generators and electrodes to include thermal coupling and feedback [3]. In 1965, Rosomoff extended the use of RF techniques for percutaneous lateral cordotomy in the treatment of unilateral pain in cancer patients [4]. In 1975, Shealy performed the first RF lesioning for chronic spinal pain when he performed posterior primary rami RF lesioning in the lumbar spine [5]. In the 1980s, Sluijter and Mehta further expanded the use of RF lesioning in the cervical, thoracic, lumbar, and sacral spine for painful spine syndromes [6]. In 1980, a very important development was the use of small-diameter electrodes, known as the Sluijter Mehta Kit (SMK) system, which were introduced for the treatment of spinal pain by Slujter and Mehta. The system consists of a 22-G disposable cannula with a fine thermocouple probe inside for temperature measurement. The smaller electrode size diminished discomfort during the procedures [6]. In the 1990s, Sluiter challenged conventional thinking that destruction of neural tissue was necessary for pain control. He suggested that pulsing the electric field could provide similar relief without thermocoagulation of the tissue. Pulsing electrical energy allowed the heat to dissipate and essentially created a nondestructive technique. Pulsing radiofrequency (PRF) was developed, in part, as a less destructive alternative to traditional heat RF [7]. Radiofrequency ablation (RFA) is the application of a higher frequency current applied to neural tissues. The circuit is made up of four components. The RF generator, an active electrode, a dispersive electrode pad and a patient to complete the circuit. The electrical fields generated cause ions in the tissues to move, generating heat, which is measured and controlled at the tip of the electrode. Lesions are generated radially from the electrode tip, at the active portion of the needle. Therefore, ideally, the tip must be placed in close proximity and parallel to the target nerve for the lesion to be effective. To ensure accurate placement of the active tip of the electrode and proper lesioning, one must utilize fluoroscopy ultrasound or other advanced imaging techniques as well as sensory and motor stimulation. Multiplanar or biplanar fluoroscopy imaging is used to target nerve roots, facets, discs, and sympathetic nerves. Additionally, water-soluble nonionic contrast dye can be used to increase specificity. Sensory testing with electrostimulation is performed at 50 Hz. Optimal placement of the active tip of the electrode can be achieved with the patient reporting concordant pain at 0.4–0.9 V. Motor stimulation should also be tested with electrostimulation at 2 Hz and 2 V. Fasciculation and/or tetanic stimulation with motor stimulation indicates placement of the electrode near a ventral nerve root and the electrode should be repositioned and motor stimulation performed again. RFA causes thermal cell death at temperatures greater than 45°C [8]. In RF, there is no consistent relationship between temperature and voltage. Therefore, temperature control RF lesioning is superior to voltage control RF lesioning for the creation of reliable and well-defined lesion sizes [9]. At greater than 60°C, soft tissues will tend to coagulate. As the surface temperature of the electrode is elevated to 80–85°C, the tissues within a short distance from the surface will be heated to a temperature of 60–65°C or greater. Therefore, once the electrode surface temperature achieves 80°C, lesion sizes propagate with time if this temperature is maintained. Most of the lesion creation occurs within the first 60 s of RF, however, there is still marked growth in lesioning between 60 and 90 s. Lesioning greater than 90 s is unnecessary, because coagulated tissue increases impedance which presents a barrier to the flow of current and therefore any further increase in lesion size [10]. As with any and all interventional pain management procedures, patient selection is paramount. The patient should be an active participant in a multidisciplinary pain program that includes a complete biopsychosocial evaluation including medical management, psychological evaluation, and physical therapy. A successful diagnostic block should be performed initially. This should be followed by a repeat diagnostic block for validation if needed, depending on the location of the injection and potential target of RF ablation. Care should be taken in performing the block and monitoring for any placebo effect. Early experiences with RFA exposed a major limitation with the technique: the conventional monopolar electrodes could create only a small volume of thermal necrosis. Major progress was achieved with the introduction of modified electrodes. These technologic advances have enabled substantial and reproducible enlargement of the volume of thermal necrosis produced with a single needle insertion, or more selective lesions in specific anatomic structures, such as the annulus or the sinuvertebral nerve. Cooled-tip electrode needles, coblation technology, expandable electrode needles with multiple retractable prolongations and directional electrode needles are in use.
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Complications of Radiofrequency Ablation Procedures
2 Medical Faculty of Istanbul University, Istanbul Pain Center, Istanbul, Turkey
3 World Institute of Pain, Atlantic Beach, FL, USA
Introduction
Historical Background
The Principles of Radiofrequency Lesioning
Inclusion Criteria
Indications
Contraindications
Types of RF
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