Radiofrequncy Ablation in Chronic Pain Management

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Radiofrequncy Ablation in Chronic Pain Management

• Joel Chang MD

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CASE

• 67 y/o M
• Lumbago, facet arthropathy, lumbar
  spondylolithesis, post-laminectomy
• Attempted Tx TENS, PT/ aqua, lidoderm,
  oxycontin, epidural
• 2 Lumbar MBBs of L3-S1 with about 1 hour relief
  each time
• Presented for pulsed radiofrequency ablation of
  L3-S1 of right MBs

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Overview

• RFA is indicated for pain with constant and
  limited distribution
• Interrupts nociceptive pathways in the treatment
  of chronic pain
• Useful for nociceptive pain and some neuropathic
  pain
• Diagnosis confirmed with diagnostic blocks first
• Tendency for recurrence 1-2 years but can be
  repeated

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Non-indications

• Centralized pain
• Pathology in the spinal cord
• Serious Psychopathology

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Diagnosis

• Diagnostic blocks are usually done before RFA
• Done only if blocks are expected to provide
  information (ex herniated disc)
• Diagnostic block utility include trigeminal
  neuralgia, and lumbar and cervical facet joint
  pain

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Diagnostic Injections

• Studies showed that single diagnostic lumbar z
  joint blocks are false positive 38 of the time.
  Blocks are usually repeated as a result
• The International Association for the Study of
  Pain specifies that diagnosis requires
  radiographically guided blocks provide complete
  relief and are validated by a appropriate control
  test that exclude false-positive responses

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RFA Sites

• Medial Branch of Posterior Ramus innervates the
  facet joints
• Dorsal Root Ganglion (herniated discs or regional
  pain syndromes)
• Intradiscal RF
• Sympathetic chain
• Splanchnic nerve
• Gasserian ganglion for trigeminal neuralgia

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RF Machine

• Includes temperature display, impedance monitor,
  stimulator, and lesion generator.
• Impedance Monitor Useful for detecting entry
  into various mediums ( a large increase for
  example might suggest movement from fluid to
  tissue)
• Electrical Stimulation Sensory stimulation
  confirms proximity to the target. Motor
  stimulation confirms a safe distance to motor
  fibers in case a heat lesion is made
• Lesioning Module continuous vs pulsed RF

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RF Machine (cont)

• When the electrode is placed on the patients
  body, a circuit is complete
• An electric field is established around the
  electrode tip. This field oscillates with
  alternating RF current causing movement of ions
  in the tissue
• This causes friction in tissue surrounding the
  catheter tip which produces heat (not the
  catheter itself)
• Monitoring the catheter tip temp therefore
  adequately measures tissue temp.

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RF Machine (cont)

• RF current is low energy, high frequency
  (100,000-500,000 hz)
• RF lesions do not selectively destroy only
  nociceptive afferents
• Temperature determines the size of the lesion
• Cells become damaged at temps 42 to 45 degrees
  celsius. With temps of 60-100 degrees celsius
  there is near instantaneous induction of protein
  coagulation, leading to cell death
• Electrical stimulation at 50 hz should produce
  sensory stimulation at less than 1 V if electrode
  is placed correctly.
• Stimulation at 2 hz should evoke contraction of
  ipsilateral paraspinal muscles below 2.5 V but
  without limb contracture.

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RF tidbits

• RFA near bone or scar tissue may have a very
  irregular ablation pattern from differences in
  impedance and conductivity leading to
  complications. Pulsed RFA is more ideal in these
  situations and less likely to lead to
  complications
• Patients with pacemakers cardiology consultation
  is needed to convert the pacemaker to a fixed
  rate for the procedure
• Patients with spinal cord stimulators
• adjustments are also needed with the settings
  (monopolar needs to be changed to bipolar and
  off)

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Technique

• RF electrodes produce little lesion distal to
  their tip and coagulate transversely
• Therefore if electrodes are placed
  perpendicularly to the nerve the may fail to
  coagulate the nerve or will coagulate the nerve
  minimally
• The most reliable coagulation is done if the
  electrodes are placed parallel to the nerve.
• Of note that some of the early studies were
  believed to be done under poor technique,
  producing poor outcomes
• Needless to say, outcome results depend on user
  experience with RFA

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Technique (cont)

• The use of preliminary electrical stimulation of
  the medial branch nerve to verify electrode
  placement is debatable.
• Some argue its an unnecessary use of time and
  that adjusting the electrode position to minimize
  the threshold for evoked activity does not
  improve outcome
• Radiological confirmation of electrode placement
  is essential

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Pulsed-RFA

• RFA 80 degrees C for 90 seconds
• Pulsed-RFA 42 degrees for 120 seconds
• Current is applied in bursts of 20 ms with a
  silent time of 480ms
• Lower temp in pulsed-RFA results in less tissue
  destruction
• Unclear Mechanism of pulsed RFA
• - modulates pain processing mechanisms
• -selectively disrupts small nerve fibers
• - Pulsed RFA associated with increased cFos

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Pulsed- RFA

• Studies show that PRF for lumbar facet joints
  tend do have a shorter benefit of pain relief (4
  months compared to 12 months for RF)
• Standard RF also denervates the multifidus
  muscle which eliminates the muscular component of
  lumbar facet syndrome

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Results

• Success for Lumbar RFA ranges from 60-90
• 21 had complete pain relief and 65 reported
  mild to mod pain relief
• Other studies showed that 60 percent of patients
  enjoy at least 80 relief at 12 months and 80
  percent enjoy at least 60 percent relief.
• 92 achieved good relief for Trigeminal Neuralgia
• Reports show that there is some loss of effect
  over 1-2 years
• Can be repeated

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Cervical RFA

• Symptoms that indicate a patient might benefit
  from cervical RFA include neck pain, headache,
  shoulder pain, scapula and upper arm pain
• Cervical MBB have a false positive rate of 1 in 3
  (lower than Lumbar but still requires diagnostic
  blocks)
• A high failure rate noted for C2-C3 Z joints 2/2
  nerves larger size and more variable course. This
  facet is innervated by the medial branch of the
  C3 dorsal ramus with a inconsistent contribution
  from the greater occipital nerve.
• Cervical anatomical variability necessitates
  multiple RF lesions per target nerve
• When pain reoccurs procedures can be repeated
• Side effects are well tolerated and serious
  complications have not been reported

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Other Applications

• RFA MB of thoracic Z joint pain, but evidence not
  as reassuring
• Also evidence for sacroiliac joint also not strong

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Repeat RFAs

• Study of effectiveness of repeat radiofrequency
  neurotomy for lumber facet pain (Schofferman,
  Kine, Spine Vol 29) showed that the frequency of
  success and durations of relief remained
  consistent after each subsequent radiofrequency
  ablation.
• Mean duration of 10.5 months and successful more
  than 85 of the time
• This 10.5 months however, is shorter than
  reported 1st time RFA relief

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To Keep In Mind

• RFA significantly improves the pain and quality
  of life in patients
• However, it does not cure the (facet) pain.

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References

• Lord, S, Bogduk, N. Radiofrequency procedures in
  chronic pain. Best Practice and Research Clinical
  Anesthesiology Vol. 16, No. 4, 597- 617.
• Mikeladze, Espinal, et al. Pulsed Radiofrequency
  application in treatment of chronic zygapopyseal
  joint pain. The Spine Journal 3 (2003) 360-362.
• Niemisto, Kalso, et al. RF Denervation for Neck
  and Back Pain A Systemic Review Within the
  Framework of the Cochrane Collaboration Back
  Review Group. Spine Vol 28, Number 16, pp
  1877-1888.
• Sluijter, M., Racz, G. Technical Aspects of
  Radiofrequency. Pain Practice, Vol 2, Number 3,
  195- 200.