Facet medial branch blocks and radiofrequency ablation

Select patients for medial branch radiofrequency ablation with a prognostic medial branch block (one block, at least 50% relief, by default), lesion parallel to the nerve with conventional probes, and repeat only after durable relief.

1. Each facet has two medial branch nerves. A lumbar facet is supplied by the medial branches at its own level and the level above. For L5–S1, the L5 dorsal ramus is targeted in the groove between the sacral ala and the S1 superior articular process ¹.
2. Select with medial branch blocks. Lumbar MBBs predict ablation outcome better than intra-articular injections. The lumbar guideline recommends a single prognostic block, accepting that dual blocks raise success rates at the cost of more false negatives ¹.
3. Use at least 50% relief as positive. Both the lumbar (2020) and cervical (2022) guidelines use at least 50% relief to designate a block positive, to maximize access to care ¹².
4. Lesion geometry drives technique. Conventional RF lesions form radially around the active tip, so electrodes should lie parallel to the nerve; internally cooled electrodes extend about 40% of the lesion beyond the tip and are often placed perpendicular ¹.
5. Repeat ablation has rules. Repeat lumbar RFA on recurrence if prior relief lasted at least about 3 months (preferably 6), and no more than twice a year ¹.
6. Imaging does not select patients. The cervical guideline finds insufficient evidence for imaging to diagnose facet pain or predict block or ablation success ².

Dual blocks or a higher threshold are reserved for selected cases, such as a younger patient with low pre-test probability or a borderline first block, not as the default ².

• L4–L5 facet: block the L3 and L4 medial branches; L5–S1: L4 medial branch plus the L5 dorsal ramus ¹.
• Perpendicular placement of a conventional RF electrode risks missing the nerve and short-lived relief ¹.
• Fluoroscopy is preferred for lumbar RFA partly because it allows parallel electrode placement ¹.
• Cervical guideline: one block before RFA absent extenuating circumstances (grade B) ².
• Sacral lateral branch RFA for SI complex pain also uses a 50% prognostic-block cut-off and targets S1–S3 ³.
• Genicular ablation for knee osteoarthritis classically targets three nerves: superomedial, superolateral and inferomedial ⁴.

• Selecting patients for ablation on MRI facet arthropathy alone ².
• Requiring two blocks with 80% relief for every patient ².
• Placing a conventional electrode perpendicular to the medial branch, which risks missing the nerve ¹.
• Repeating ablation monthly while some relief continues, or treating RFA as a single lifetime procedure ¹.