Radiofrequency ablation of Nerves
The application of Radiofrequency (RF) techniques has increased many folds in Pain Management over the last few decades. Radiofrequency lesioning refers to the delivery of high frequency electrical current in the RF range i.e 500 KHz to patient tissue via an RF electrode to induce a biological effect, such as thermal destruction of nerves that carry painful impulses.
RF methods used in Pain Management can be divided based on waveform/ set temperature
a) Thermal RF – Thermal nerve ablation with continous RF waveform & temperature in 70-90 degree C.
b) Pulsed RF – RF delivered in short high intensity bursts with temperature at or below 42 deg C. It causes neural modification by electric and thermal fields.
Radiofrequency lesioning is carried out by inserting RF cannula under C Arm fluoroscope guidance under local anaesthesia. The preparation and post procedure precautions are almost the same as any other interventional pain block. The standard equipment required for RF lesioning includes RF generator, electrode and RF cannula.
The applications of Radiofrequency lesioning in Pain Medicine are numerous:
- Facet Joint Dennervation – Radiofrequency dennervation of the facet joint is the only validated treatment for lumbar and cervical facet syndrome after dual diagnostic blocks with local anaesthetic have been successful in abolishing pain.RF ablation of Medial branch nerves is done by inserting RF cannula under fluoroscopic guidance and the needle tip is positioned in the bony groove from where the nerve passes before entering the joint. After checking sensory stimulation and multifidus muscle contraction on motor stimulation, lesioning is done after setting the parameters.
- Trigeminal Ganglion RF ablation – Trigeminal ganglion RF ablation is used in cases of Trigeminal Neuralgia with intermittent neuralgic pains involving the face and mandibular region.The trigeminal ganglion is located in the meckels cave in the skull base. The RF cannula is entered through the cheek after locating the foramen ovale under C Arm fluoroscope. Once the needle enters the foramen ovale sensory and motor stimulation is done to determine the proximity and the division of nerve stimulated. Thereafter RF lesioning is done with three lesions given at around 70 degree Centigrade temperature.
- Radiofrequency Genicular Nerves – RF genicular nerves is used in advanced cases of osteoarthritis knee joint. Three of the six genicular branches can be approached under C Arm fluoroscope and can be lesioned after determining proximity by checking sensory stimulation. Two lesions are given for each genicular nerves. Usually this is preceded by local anaesthetic block of the genicular nerves as RF lesioning for other nerves.
- Intradiscal RF Treatment – Discogenic pain (Degenerative disc disease) is diagnosed by performing discography. Positive discography is indicated by increase in the concordant pain on increasing pressure within the disc and detecting tears in the disc. The treatment of discogenic pain involves interventions in the form of Biaculoplasty, IDET which are again done after inserting the electrodes through the cannula placed percutaneously into the annulus fibrosus portion of disc and lesioning the nerve endings carrying pain from the disc.Another interventional procedure that has gained scientific evidence is L2 Ramus Communicans block. Ramus communicans are the sympathetic fibres innervating the disc and are thought to carry such pain signals from the disc to the central nervous system.Initially a diagnostic Ramus Communicans block at L2 level is given on both sides with local anaesthetic agent. If this is effective in abolishing pain and lasting more than the duration of effect of LA, patient is kept for a Radiofrequency lesioning of the L2 Ramus Communicans, which provides long term pain relief to the patient.
- Lumbar Sympathetic RF Lesioning – Radiofrequency lesioning of lumbar sympathetic chain is done in cases of sympathetic mediated pains in CRPS (Complex Regional Pain Syndrome) involving lower limbs. Splanchnic, Ganglion impar RF and Stellate ganglion RF are other sympathetic RF lesions used clinically.A local anaesthetic block is first given to block lumbar sympathetic plexus and if effective in alleviating pain outlasting the effect of local anaesthetic, then RF lesioning of sympathetic chain is planned. It is done again by inserting RF cannulas percutaneously from the back paramedian region under fluoroscopic guidance and targeted towards the vertebral body at the lumbar levels. Once proper position is achieved under C Arm fluoroscope, RF lesioning is done at set parameters.
- Sacroiliac Joint Dennervation – Sacroiliac joint RF dennervation is done in cases where the intraarticular steroid injection provides short lasting relief requiring repeated such injections. This is usually seen with degenerative Sacroiliac joints rather than the inflammed joints.Many techniques of SI joint dennervation are described but we follow the bipolar technique utilizing simultaneously two electrodes through parallel cannulas placed 1 cm apart on the sacrum at the back. Along with this Medial branch RF is also carried out at L4 and L5 level.
- Pulse Radiofrequency (PRF) of Dorsal Root Ganglion (DRG) – The Dorsal root ganglion is located on the proximal most part of sensory nerves near the spinal foramen. The Pulse RF is used in both cervical and lumbar DRG for Radicular pain.Cervical DRG PRF is used in cases of brachial plexopathy secondary to nerve injury, soft tissue carcinoma giving rise to radicular symptoms in the upper limb. It involves placing the RF cannula near the DRG under fluoroscopic guidance and confirmed by stimulation. The use of PRF quite reduces the likelihood of any motor weakness post procedure.Lumbar DRG PRF is indicated in recurrent cases of lumbar radicular syndrome. PRF works on the principal of neural modification by the electrical and thermal fields and is effective in providing longer relief in radicular symptoms compared to the Epidural steroid injection.
- Suprascapular Nerve PRF – Pulse RF has been used on some of peripheral nerves like the Suprascapular Nerve, which provides innervation to the shoulder joint. This is indicated in Shoulder joint osteoarthritis or other pains originating in the shoulder joint. As Suprascapular Nerve gives motor supply to muscles around the shoulder girdle, thermal RF is therefore not very suitable as it can lead to motor weakness.