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Controversies in RF Neurotomy: Sensory Stimulation

Controversy I: Voltage vs Current. The voltage induced into the body serves as a ?potential" for current to flow, but does not determine the direction of the current flow: this is determined by tissue impedance. Voltage measurement does not correlate with the current flow through tissues nor the

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Controversies in RF Neurotomy: Sensory Stimulation

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    1. Controversies in RF Neurotomy: Sensory Stimulation algosresearch.org

    2. Controversy I: Voltage vs Current The voltage induced into the body serves as a �potential� for current to flow, but does not determine the direction of the current flow: this is determined by tissue impedance. Voltage measurement does not correlate with the current flow through tissues nor the electrophysiological effects of such current.

    3. Example of Effects of Impedance on Current Flow Lightening strike victims with dry skin have high impedance and usually suffer serious skin burns but may escape internal organ damage Victims with wet skin have low skin impedance permitting current to flow to internal organs and blood vessels�this current flow to these organs leads to amputation or serious internal organ damage

    4. Absolute Voltage Value is Not Important with Respect to Tissue Damage Patients may have electrical injuries from 220V that are just as severe as 2000V. It is the differential current flow throughout the tissues of differing impedance that determine the degree of injury.

    5. Coulombs Law Stimulating electrical force is proportional to the inverse radius squared Therefore the distance the stimulating electrode to the nerve is proportional to 1/(Square root of the current flow between the nerve and the needle tip)

    6. All stimulation devices designed for accurate stimulation measure current, not voltage. Voltage is fixed during stim.

    9. Convention in RF for Pain Medicine is VOLTAGE Stim, not Current All 7 manufacturers have voltage adjustable stimulation available on their RF Generators. Only 3 have current stimulation options Teaching at all national conferences in pain medicine and RF Manufacturer conferences use VOLTAGE STIMULATION, Fixed current Literature in pain medicine uses VOLTAGE STIMULATION, fixed current

    11. Controversy II: Use of a Long Unshielded Needle Tip for Stimulation All stimulating needles used for accurate nerve stimulation are shielded to the tip and have a very small exposed surface area. Typical exposed length of a stimulating needle is 0.37mm Ion flux at the tip is focal when using a shielded electrode

    13. Uninsulated Electrodes Do Not Provide Significant Current vs Distance Gradient

    14. RF Needle Active Tips are Typically 500% to 5000% Longer than Stimulating Needles Tips Effectively, these are uninsulated needles for the purpose of stimulation since the current flow occurs all along the active tips reducing the sensory discrimination due to non-focal current flow

    15. Controversy III: Differential Impedances Along A Long Active Tip The long active tips (10-15mm) used in lumbar medial branch neurotomy must pass through several tissues and may not lie completely within the same tissue. For instance, the tip may be partially in the multifidus muscle, the mammillary-accessory ligament, periosteum, adipose, and nerve tissue

    16. Differential Current Flux Bench studies and electro physics studies demonstrate differential current flux through each of the tissues through a single needle with a long active tip The measured impedance will be a geometric average of the individual tissue impedances, that may inaccurately reflect a low impedance and erroneous needle placement

    18. Controversy IV: Stimulation Using Unshielded Tips Will Simultaneously Stimulate Several Tissues Innervated within the Neural Field Can patients discern the difference between multifidus muscle or fascia, periosteum, z-joint capsule, medial branch, or the dorsal ramus during sensory stimulation?? It is unlikely since these are all within the same neural field and are very close together anatomically.

    19. Controversy V: How to Best Accurately Place Needles for RF Neurotomy ISIS Guidelines eliminate stimulation for some of the above reasons Placement of an initial Stimuplex or other shielded needle initially then placing a RF needle fluoroscopically to the point of maximum sensory stim as defined by the stimulating electrode Use of a small gauge long stimulating electrode through the RF needle (18ga). Once accurate stimulation is achieved, slide the RF needle to the tip of the stimulating needle Redesign of the RF system may be needed Use of CURRENT STIMULATION instead of Voltage

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