Overview
Medial branch blocks (MBBs) are fluoroscopically guided injections of local anesthetic onto the medial branch nerves — small nerves that carry pain signals from the spinal facet joints. They serve as the gold-standard diagnostic test to confirm facet joint-mediated pain before proceeding to radiofrequency ablation (RFA). The medial branch nerves are purely sensory nerves supplying the facet joints; blocking them with local anesthetic temporarily 'turns off' facet joint pain, confirming its presence and predicting the likely response to RFA.
Why Medial Branch Blocks Are Performed
Facet joint degeneration is extremely common on MRI and does not reliably predict who has clinically significant facet pain. Medial branch blocks provide a biological test of the facet joint's contribution to a patient's pain — essentially asking: if we temporarily anesthetize the nerve supplying this joint, does your pain improve? A positive response (typically defined as ≥50% pain relief during the block's duration) confirms facet joint involvement and predicts a favorable response to radiofrequency ablation.
The Procedure
Medial branch blocks are performed under fluoroscopic guidance with the patient lying comfortably on the procedure table. Local anesthetic is used to numb the skin. Fine needles are placed at precise anatomical landmarks at each facet level to be tested, and a small volume of local anesthetic is deposited. Patients are asked to document their pain levels over the next several hours while the block is active.
From Diagnosis to Treatment
Most pain medicine guidelines recommend two confirmatory medial branch blocks (dual blocks) before proceeding to radiofrequency ablation, to reduce false-positive results. Once facet-mediated pain is confirmed with positive MBBs, RFA of the corresponding medial branches provides durable, longer-lasting relief without repeated injections.