What is the role of a medial branch nerve block in the workup of lumbosacral facet syndrome?

Updated: Nov 19, 2018
  • Author: Gerard A Malanga, MD; Chief Editor: Craig C Young, MD  more...
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Given that no historical or physical examination maneuver is unique or specific to Z-joint–mediated LBP, fluoroscopically guided medial branch nerve injections are often used for diagnostic purposes to determine whether the Z-joint in question is responsible for LBP. Once the Z-joint is established as the pain generator, more definitive treatment options, such as radiofrequency ablation, are offered. A Z-joint injection may also be used for therapeutic purposes, but many consider this procedure more challenging to perform.

Given the dual innervation of each Z-joint, one must anesthetize or block the cephalad and subadjacent medial branches (eg, anesthetize the L3 and L4 medial branches for the L4-L5 Z-joint). Injections are diagnostic if patients report significant relief of symptoms, usually at least a 50% reduction in pain. Although the optimal number of blocks prior to radiofrequency denervation is uncertain, most guidelines, including the Spine Intervention Society (SIS) and the North American Spine Society (NASS), recommend a positive response to 2 screening medial branch blocks with at least 80% relief on 2 occasions for radiofrequency ablative denervation  to be done. [20]

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