Radio Frequency Ablation (RFA) is a technique where a needle/probe is placed next to a nerve and presumably by increasing the temperature to 80 degrees Celsius, the nerve is ablated or destroyed. This technique is still the recommended choice for the medial branch nerves of the spine facet joints, as these nerves have also only very minor sensory input to the skin and minor motor or muscle function. Thus by doing RFA at this location, one does not typically see significant numbness or weakness. However, if one does RFA on a nerve such as the nerve roots or a mixed peripheral nerve, then one may experience numbness and weakness.
Pulsed Radio Frequency (PRF) technology, helps to overcome this by pulsing the radio frequency energy to the nerves, and thus with temperatures not exceeding 42 degrees Celsius, the nerves are not destroyed, and there is no numbness or weakness. The PRF gives pain control by reversibly disrupting the transmission of the pain fibers.
The mechanism, although not certain, may work similar to TENS or spinal cord stimulation, causing neural plasticity changes within the central nervous system, but with a more direct effect on the selected nerve. Theories proposed include an electric and/or magnetic field being created by the voltage fluctuations. With PRF, the voltage (45 V) is actually higher than with RFA (15-25 V), because with pulsing technology, there are intervals in which no current is applied and thus the heat is allowed to dissipate. Interestingly, gene expression within the spinal cord by activation of a protein, C-Fos, may also contribute. These resultant changes are not permanent, so repeat PRF may be required.
In summary, PRF may cause changes within the pain nerve cell membranes and inhibition of synaptic transmission and without numbness or weakness. This allows PRF to be utilized on the mixed peripheral nerves, sensory nerves, and nerve roots, whereas with traditional RFA, this would cause numbness or weakness.
COMMON EXAMPLES WHERE PRF IS UTILIZED:
1. Mixed peripheral nerves and sensory-only peripheral nerves.
Suprascapular nerve for shoulder pain.
Femoral nerve for thigh pain status post femoral arterial access for percutaneous cardiac procedures.
Intercostal nerve for thoracic/chest pain status post thoracotomy.
Ilioinguinal or genitofemoral nerves status post hernia repair.
Lateral femoral cutaneous nerve for Meralgia Parasthetica, or anterolateral thigh pain.
Greater occipital nerve for occipital headaches.
2. Trigger points
Myofascial or muscle pain.
3. Nerve root/dorsal root ganglion.
Failed back surgery syndrome.
Status post hernia repair.
Metastatic breast cancer.
Status post breast cancer surgery.
Status post thoracotomy.
4. Gray ramus communicans.
Vertebral compression fractures.
Metastatic spinal lesion.
To determine if one is a candidate, a diagnostic block of the specific nerve is done first with a numbing agent or local anesthetic. If the patient achieves greater than 75% relief, the PRF can be considered. The PRF of the peripheral nerves and for the trigger points of myofascial pain are typically done with ultrasound guidance. The nerve root-dorsal root ganglion and gray ramus communicans PRF procedures are done with x-ray guidance.