Diagnostic Medial Branch Nerve Blocks

These are diagnostic injections where the main purpose is to help diagnose the cause of neck or back pain by either confirming or ruling out the spinal facet joints as the pain generator. Typically these are done in preparation for pain treatment procedure/injection called radiofrequency nerve ablation. If the diagnostic blocks are positive (meaning there was immediate and significant pain relief after the block) then the radiofrequency ablation would be the next step. If the blocks were negative (meaning no relief at all or minor relief) then the ablation would not be recommended. 

What is being injected?

In this type of injection the medication that is injected is an anesthetic that will “numb” the nerve. The most common anesthetics used are usually lidocaine or bupivacaine, among others. 

What it does

The anesthetic injected blocks the nerve interrupting the transmission of the nerve impulse. What this does is “numb” the area that is innervated by the targeted nerve. The nerve will be blocked or “numb” for as long as the anesthetic is active, ranging from 2-3 hours to 6-8 hours depending on which anesthetic is used. During this time period it’s important to know if the pain has been reduced or not because after the anesthetic wears off the effect does not count and the result is not valid.  Again, the block is deemed  positive if there is immediate and significant pain relief and is deemed negative if there was no relief at all or minor relief.

What it doesn’t do

Being a diagnostic block this injection does not have any intended therapeutic effects. The only purpose is diagnostic and there is no expected pain relief beyond the duration of the block. On a rare occasion some patients may get a therapeutic effect that lasts beyond the block but this is very rare and not well understood. 

Then why do them?

Most commonly these injections are recommended in preparation for treatment with radiofrequency nerve ablation (RFA).  The RFA is used to treat neck and back pain due to facet joint arthritis. To use RFA one must have neck or back pain coming from the facets joints. While this pain diagnosis can be supported by physical exam as well as MRI findings, the diagnostic blocks are medically necessary to confirm the diagnosis prior to attempting the RFA treatment.  Usually two blocks are needed, and both need to be positive before proceeding with the RFA.   If RFA is not the intended purpose the other reason to have these blocks would be to confirm diagnosis of pain when there are multiple abnormalities on MRI/Xray, uncertain or confounding physical exam findings or unclear history.

What are the risks?

Overall considered safe when performed with fluoroscopic (xray) guidance by a physician specialized in interventional pain management. Preferably one who is  board certified and fellowship trained.  Risks are similar to other spine interventions and include infection, bleeding, allergic reaction, pain aggravation, nerve injury, and paralysis (rare).