Dr.Moallemy Radiofrequency Lesioning

Dr.Moallemy  Radiofrequency (RF) current is used in pain medicine to make discrete therapeutic lesions in various targets throughout the nervous system.  The technique is most frequently used to block nociceptive signals from reaching the central nervous system and thereby anesthetize the source of the pain.  RF is implemented percutaneously by means of an insulated needle with a metal active tip that is placed in the appropriate nerve pathway.  Before the introduction of modern RF equipment, various techniques (e.g.,cryosurgery and chemical neurolysis) were used in an attempt to produce localized nervous system lesions; however, none have been as widely used or are as effective as RF.

Dr.Moallemy  The use of electricity to treat pain was first described in 1931, when direct current was applied to the gasserian ganglion for the treatment of trigeminal neuralgia.  Because the frequencies used (350 to 500 kHz) were also used in radio transmitters, the procedure was termed radiofrequency.  An RF lesion generator is a device used to produce lesions in nervous system or other tissue by the direct application of high-frequency current to selected sites.  A typical RF lesion generator has the following systems: continuous impedance monitoring; nerve stimulation; monitoring of voltage, current, and temperature; and pulsed current delivery mode.

Dr.Moallemy Image of a radiofrequency generator.

Dr.Moallemy  The energy is focused around the active tip of the electrode and activates charged molecules(mainly proteins) to oscillate with the rapid changes in alternating current. This produces friction in the tissue that causes heat formation directly around the active tip.  The grounding electrode serves to complete the circuit and to disperse heat buildup, thereby preventing a burn of the skin.  RF energy can be applied as either continuous or pulsed current.  Continuous RF current heats the tissue surrounding the electrode and lyses the targeted nerve. On a pathologic level, continuous RF current heats nerve fibers and results in wallerian degeneration. On a physiologic level, continuous RF current destroys all fiber types within a nerve and is not selective for any one fiber type.  Pulsed RF (PRF) delivers RF current in small bursts and thus prevents the accumulation of heat around the electrode... 

Dr.Moallemy Radiofrequency Lesion Generator :  Continuous Impedance Monitoring:impedance monitoring is primarily used to confirm continuity of the electrical circuit. However, in the pulsed mode, impedance monitoring is more crucial because the strength of the electrical field is decreased when impedance is high.  Nerve Stimulation: the two types of stimulation are sensory and motor. Sensory stimulation occurs at 50 Hz and is used to determine the distance between the electrode and the targeted nerve fiber. Motor stimulation occurs at 2 Hz and is used to determine whether a needle is placed too close to motor fibers,   Monitoring of Temperature:  Monitoring of Voltage:  Monitoring of Current: 

Dr.Moallemy Continuous Lesioning  The heat generated in the continuous mode causes tissue coagulation in a small, discrete oval surrounding the active tip of the electrode.  to coagulate the largest area of nerve fibers reliably, the electrode must be positioned parallel to the nerve.  The size of the lesion depends on several factors: Tissue temperature Duration of coagulation, Gauge of electrode and length and gauge of active electrode tip:  efficacy is maximized when needle placements anatomically precise, when larger (e.g., 18- to 20-gauge) needles are used, and when multiple parallel lesions are generated (within one needle width from each other) to account for the variable nerve topography..

Dr.Moallemy

Pulsed Lesioning  The therapeutic effect of PRF lesioning is thought to be the result of the electrical field, rather than of the thermal effects. The aim of PRF is done by delivering short bursts of energy (20 milliseconds) twice per second, followed by a quiet phase (lasting 480 milliseconds) during which no current is applied. This approach allows for heat dissipation, thus keeping the tissue temperature lower than the neurodestructive threshold of 45°C. Voltage in the continuous mode is 15 to 25 V, compared with 45 V in the pulsed mode. Because the electric field is strongest at the tip of the electrode, it is recommended that electrodes be placed perpendicular, rather than parallel, to the targeted nerve during creation of a PRF lesion PRF current appears to have both thermal and nonthermal effects.

Pulsed Lesioning (continued)  The nonthermal effects may be attributed to an effect on the function of voltage-gated ion channels.  It would appear that the best use for this modality is in the treatment of radiculopathies and painful peripheral neuropathies.  it is recommended that electrodes be placed perpendicular, rather than parallel, to the targeted nerve during creation of a PRF lesion. PRF lesioning is traditionally considered safer than continuous RF because it has no reported neurologic side effects. Dr.Moallemy