radiofrequency procedures in chronic pain

Radiofrequency procedures Radiofrequency procedures in chronic painin chronic pain

R2 Guo, Shu-lin

92.5.2

IntroductionIntroduction

Radiofrequency

– A tool used for creating discrete thermal lesions in neural pathways in order to interrupt transmission

– A procedure that generates heat around the tips of an electrode to denature nerves, interrupt nociceptive pathways, and thereby treat pain

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Radiofrequency (RF) current is low energy, high frequency (105-5*105 Hz), alternating current

When applied to biological tissue, this current causes charged molecules to oscillate with the rapid changes in alternating current

The resulting friction in the tissue produces heat

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Generation of an RF lesion required a circuit:

– A ground plate with a large surface area applied to the patient

– The other arm is connected to an electrode whose top lies in contact with the target tissue

– Current flows between electrode tip and ground plate

Needle electrode

Ground plate electrode

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Due to the large difference in their surface areas, at the ground plate current is of insufficient density to damage tissues

At the uninsulated electrode tip, current is concentrated and achieves sufficient density to denature tissues

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An equilibrium between heat generated and heat lost to surrounding tissues, and on electrode size

Thermal energy ≈

Current2 Χ log( Constant Χ Time)Distance4

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Heat production

– Heat is greatest in the tissue immediately surrounding the tip and decreases rapidly with increasing distance from it

– Most significant lesion expansion occurring between 0 and 60 seconds at the target temperature

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Heat loss

– Heat loss occurs via diffusion through surrounding tissues (conduction) and via the circulation (convection)

– Current may be dissipated or drained by fluids such as CSF or hematoma in the region of the electrode, in which event the target tissue may escape critical heating

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Monitors

– Earlier devices relied on monitoring the magnitude of the current delivered

– The development of thermistors and thermocouples allowed actual tissue temperatures to be monitored directly

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Lesion

– The volume of tissue denatured by the heat assumes the shape of an egg around the uninsulated tip of the electrode

– Large tips produce larger lesions

– The electrode coagulates tissues to a distance from its surface equivalent to 1 to 1.5 times the diameter of the electrode

– The length of the lesion is basically the length of the uninsulated tip of the electrode

Before RF After RF

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RF electrodes

– Hollow or solid-state

– Hollow needle electrodes allow agents to be injected but required that the stylet be replaced by a fine thermocouple during temperature monitoring

– Solid electrodes permanently embody a thermocouple

Pathophysiology of lesionsPathophysiology of lesions

In the past, Letcher and Goldrong reported Aβ,Aδand C fibers exhibited differing susceptibilities to blockade by RF and heat

In vivo showed that RF lesions of 45-85C produce non-selective destruction of nerve fibers

Post-operative EMG studies have shown destruction of αmotor neurons by RF lesions that successfully relieve pain

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Trigeminal neuralgia

– RF neurotomy is one of the surgical options for patients intolerant or resistant to pharmacotherapy

– RF neurotomy is more effective than peripheral surgery and most suitable for patients of advanced physiological age, poor medical condition, and younger patients who do not accept the risks of posterior fossa surgery

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Trigeminal neuralgia

– An RF electrode is inserted under fluoroscopic guidance through the foramen ovale and electrode position is checked by electrical stimulation

– When the patient reports paresthesia in the distribution of their usual symptoms, general anesthesia is reinstated and an RF lesion is generated

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Trigeminal neuralgia

– Facial sensory deprivation and dysaesthesia

– Lesions of the ophthalmic division cause corneal anesthesia

– The motor root (masseter contraction) lies medial to the ganglion

– Intracranial hemorrhage appears to be the most common cause of perioperative death

Motor division of CN V

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Trigeminal neuralgia

– The goal should be to achieve dense hypoalgesia to pinprick in the symptomatic divisions; this is associated with the best risk : benefit profile

DREZ RFDorsal rhizotomy

Dorsal root ganglia RF

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Dorsal rhizotomy and dorsal root ganglion procedures (partial rhizotomy)

– The spinal dorsal roots and dorsal root ganglia (DRG) are the anatomical equivalent of the trigeminal sensory roots and ganglion

– The risk : benefit ratio of this application appears unfavorable, so patients should be thus informed

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The dorsal root entry zone (DREZ)

– Nashold’s RF DREZ procedure aimed not only to disrupt Lissauer’s tract but also to destroy second-order neurons in the substantia gelatinosa thought to be responsible for denervation hypersensitivity

– An electrode with 0.25mm diameter and 2 mm exposed tip is inserted to a depth of 2mm in the DREZ and lesions generated at 1mm intervals (about 10-15 lesions per segment)

Lissauer’s tract

Facet Joint

Facet Nerve

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Lumbar medial branch neurotomy

– The facet joints are paired synovial joints and have dual innervation from the medial branches of the dorsal rami that pass immediately above and below each joint

– Electrodes introduced parallel to the nerve are more likely to incorporate the nerve than are electrodes introduced perpendicularly

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Cervical medial branch neurotomy

– Anatomical studies confirmed target points for the cervical medial branches but revealed a degree of anatomical variability that necessitates the creation of multiple RF lesions per target nerve

– Pain recurs relief can be reinstated by repeat procedures

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Other applications

– RF lesions have been applied to the peripheral autonomic nervous system with the theoretical aim of interrupting visceral nociceptive afferents for the treatment of intractable cancer pain or the sympathetic efferents for the treatment of sympathetically maintained pain

– Targets have included the upper thoracic sympathetic chain, the major autonomic ganglia – sphenopalatine, stellate, and lumbar – and the grey rami communicans

Sympathetic chain

SummarySummary

Successful factors

– Knowledge of the nerve’s anatomical course, variations and relations; an appreciation of 3D radiographic landmarks, and extremely precise electrode placement

Good results

– Trigeminal neuralgia, and cervical and lumbar facet joint pain

Thank you for your Thank you for your attention.attention.

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