Nerve destruction using chemicals to promote analgesia had been extensively used in the early part of the 20th century for management of pain. With the advent of newer analgesics and the development of safer techniques for pain management, its use has markedly diminished. However, recent neurodestructive techniques for pain management such as radiofrequency lesioning resulted in a surge of interest in this method of pain relief. Presently, these procedures are available as part of the management option for chronic pain and its use is usually based on the expertise of the pain specialist and the felt need of a selected group of patients.
Radiofrequency lesioning is the application of electrical current to promote thermocoagulation and nerve destruction. It is used to ablate pain pathways in the trigeminal ganglion, spinal cord, dorsal root entry zone, dorsal root ganglion, sympathetic chain, facet joints, and peripheral nerves. Since it causes nerve destruction, this technique is utilized only as end of the line therapeutic modality when other measures have failed. Fluoroscopic guidance is a requirement for proper needle placement.
Mechanism of Radiofrequency Lesioning
Frictional heat is generated by molecular movement in a field of alternating electrical current at radiofrequency. An electromagnetic field is created around an active electrode when the frequency is set above 250 kHz. The active electrode is placed at the site for lesioning. Heat is generated as current flows through a probe with a built in thermocouple needle. The heat is not emitted from the probe itself but from the current movement which generates the heat as it passes through the tissues.
The lesion is formed once the neural temperature exceeds 45 degrees centigrade. Temperature above ninety degrees centigrade can cause boiling and tissue tearing with electrode removal. the temperature is monitored and wattage is adjusted to the desired level, which in turn determines the size of the lesion. Lesion plateaus with time. After sixty seconds at a certain temperature, lesion growth is minimal. The lesion is spheroidal and may extend several millimeters beyond the active electrode tip, but the majority of the lesion volume surrounds the axis of the active electrode. The cross sectional diameter of the lesion is generally 5-6 cm. Prior to lesioning, pain is first replicated using higher frequencies and lower voltages. Once the target tissue is localized, thermocoagulation is instituted.
Complications of Radiofrequency Lesioning
Post-lesioning neuritis/neuralgia- pain may be worse than the original pain. It is observed in as much as 10 percent of patients; numbness, motor paralysis, pneumothorax, Horner’s syndrome, and incomplete pain relief .