The nerve, not the joint

Each facet joint in the spine gets its sensation from two small nerves called medial branches, and it is those nerves — not the joint capsule itself — that get anesthetized here. A thin needle is walked under fluoroscopy to the point where the medial branch crosses a specific bony landmark, local anesthetic is deposited, and if that joint was the source, the pain it was generating should drop sharply within minutes.

That is a different target than an intra-articular facet injection, which puts medication inside the joint itself. The distinction matters because the medial branch block is built to be a diagnostic instrument first. It is not trying to treat anything on the day it is done — it is trying to find out, with more certainty than an MRI ever will, whether this joint is worth treating at all.

The false-positive problem, stated honestly

A single medial branch block, done once, is wrong often enough that no responsible practice should act on it alone. Placebo response, sedation effects, and local anesthetic spreading to a neighboring structure all produce relief that has nothing to do with the joint being tested — and published false-positive rates for a single lumbar block run high enough that acting on one is closer to a coin flip than a diagnosis.

The fix is a comparative or dual block: the same joint tested twice, on separate visits, using local anesthetics with different durations of action — a short-acting agent one time, a long-acting agent the other. If the joint is truly the generator, the length of relief should track the length of the anesthetic’s known action both times. Relief that does not track duration, or that shows up after the saline control some protocols use, is telling you the joint was never the answer.

Lumbar and cervical, the same logic pointed at different geography

Both are done the same way — fluoroscopic guidance, contrast where the technique calls for it, small volumes placed precisely — and both are read the same way: concordant relief on two separate, differently-timed blocks, not a single good day.

What a percentage of relief actually means

Guidelines differ on the bar — some accept 50% relief as a positive block, others hold the line at 80% — and the choice is not academic. A stricter threshold produces fewer false positives and a cleaner group of patients moving to radiofrequency ablation, but it also disqualifies some patients who were genuinely helped, just not helped enough to clear the bar. This practice runs the stricter standard on purpose: burning a nerve that was never the problem costs the patient a procedure and costs the next diagnostic step its credibility.

Worth naming directly: a patient carrying significant metabolic inflammation can have a lower baseline pain threshold and a noisier response to any local anesthetic, which is one more reason a single block is not enough evidence on its own, and one more reason the bloodwork conversation and the joint conversation happen in the same visit rather than two separate ones.

Why this comes before, never after

Radiofrequency ablation destroys the medial branch nerve to stop it from carrying pain signal. That is not a step to take on a guess. A confirmed, concordant, comparative block is the gate that has to be cleared first, and this practice will not skip it even when a patient is confident about which joint is at fault — confidence is not concordance, and the two are not the same thing.

What happens on the day

Common questions

Related reading

• Facet joint pain
• Radiofrequency ablation
• Facet joint injection
• Occipital neuralgia
• How long does a nerve block last?