Radioablation (Radiofrequency Ablation) of Chronic Pain

Definition

Mechanism of Action

• High-frequency alternating current is delivered via a monopolar or bipolar electrode placed adjacent to the target nerve.
• The current causes ionic agitation in surrounding tissue, generating frictional heat (above 60-80°C for conventional RFA).
• This produces coagulative necrosis and Wallerian degeneration of nociceptive A-delta and C-fibers, disrupting the pain arc.
• Pulsed RFA uses short bursts of current at lower temperatures (<42°C), causing neuromodulation rather than destruction - the exact mechanism is unclear but involves membrane electroporation and inhibition of synaptic transmission.

Types of RFA

Indications

1. Spinal/axial pain - Cervical, thoracic, and lumbar facet joint (zygapophyseal) pain - most common use; targets medial branches of dorsal rami
2. Chronic neck pain - Post-whiplash syndrome
3. Sacroiliac joint dysfunction
4. Genicular nerve ablation - Knee osteoarthritis pain (FDA-approved cooled RFA device: Coolief)
5. Trigeminal neuralgia and occipital neuralgia / chronic headache syndromes
6. Sphenopalatine ganglion ablation - Migraines and cluster headaches
7. Cancer-related pain - Upper abdominal cancers (gastric, pancreatic) via celiac plexus
8. Complex Regional Pain Syndrome (CRPS)
9. Intercostal neuralgia, peripheral neuropathy

Contraindications

• Local or systemic infection / sepsis
• Coagulopathy or active anticoagulation (relative)
• Implanted cardiac devices (pacemakers, defibrillators) - especially monopolar RFA
• Pregnancy
• Patient unable to consent or cooperate
• No response to prior diagnostic nerve block

Procedure (Stepwise)

1. Patient preparation - Imaging review, informed consent, IV access, standard monitoring
2. Positioning - Prone for lumbar; supine for cervical or knee procedures
3. Imaging guidance - Fluoroscopy (most common), CT, or ultrasound
4. Needle/probe placement - Insulated needle with active tip placed parallel to the target nerve (parallel placement maximises lesion overlap)
5. Stimulation testing - Sensory stimulation at 50 Hz should reproduce concordant pain at ≤0.5V; motor stimulation at 2 Hz at >1.5-2x sensory threshold confirms no motor root proximity
6. Ablation - Local anesthetic injected, then current applied (60-90°C for 60-90 seconds for conventional RFA)
7. Post-procedure - Short observation period; NSAIDs or corticosteroid may be injected to reduce post-procedural neuritis

Outcomes and Duration of Relief

• Conventional RFA: pain relief lasting 6-12 months or longer; effect ends when the ablated nerve regenerates (axonal regrowth)
• Cooled RFA for knee pain: benefits persisting up to 18-24 months
• Repeat ablation is feasible once the nerve regenerates and pain recurs
• RFA has been shown superior to steroid injections for certain spine-related pain conditions

Complications

• Post-ablation pain flare (most common) - treated conservatively with NSAIDs
• Transient neuritis
• Bleeding, hematoma at puncture site
• Allergic reaction to local anesthetic or contrast
• Inadvertent thermal damage to non-target structures (skin burns, muscle necrosis)

• Infection / abscess
• Persistent neuropathic pain or dysesthesia
• Motor deficit (if motor nerve inadvertently ablated)
• Depigmentation or skin changes over ablation site
• Flaccid paresis (if anterior ramus damaged)

Summary Points for 5-Mark Answer

• RFA = high-frequency current (300-500 kHz) → heat → coagulative necrosis of nociceptive fibers
• Three main types: conventional (thermal), pulsed (neuromodulation), cooled (larger lesion)
• Mainly targets medial branches of dorsal rami for facet pain; also used for genicular, trigeminal, sacroiliac, and cancer pain
• Requires prior diagnostic nerve block to confirm target
• Relief lasts 6-12+ months; repeatable when nerve regenerates
• Key complications: post-ablation flare, neuritis, infection, thermal injury to adjacent structures