DIAGNOSTIC MEDIAL BRANCH BLOCK
The only test that finds facet pain. There is no scan for it.
This is a test, not a treatment, and understanding that distinction is most of what makes it work. A small volume of local anesthetic is placed on two named nerves. If your pain goes while it is working, the joint those nerves serve is the generator. If it does not, we have excluded something real and we look elsewhere.
The anatomy the test depends on
Each lumbar facet joint receives its nerve supply from the medial branches of the dorsal rami at two levels — the level of the joint and the one above. Those nerves run in a predictable bony groove, which is why they can be reached reliably under fluoroscopic guidance and why the target is a landmark rather than a guess.
Because they are purely sensory to the joint and its immediate tissue, anesthetizing them produces a clean experiment: the joint stops reporting and nothing else changes. That is the closest thing this field has to a controlled test of where pain is coming from.
What happens on the day
- You rate your usual pain before we start, and describe the movements that reliably reproduce it. This baseline is what the whole test is measured against, so it is worth being precise rather than stoic.
- You lie face down. The skin is cleaned and numbed with a small injection of local anesthetic, which is the part most people find least comfortable.
- Under live fluoroscopy, a fine needle is placed on each target — usually two or three per side. Position is confirmed on two views before anything is injected.
- A small volume of local anesthetic goes onto each nerve. Small is deliberate: a large volume spreads to structures that are not the target and turns a specific test into a vague one.
- You get up and move. Deliberately, into the positions that normally hurt. A test where you lie still afterward tells us almost nothing.
- You keep an hourly record for the rest of the day, on paper we give you. This is the result. Not an impression the following week — hours, with numbers.
The whole appointment is short. No general anesthetic is used, and none is needed — you have to be able to report what you feel, which is the point.
How to read your own result
A CLEAR POSITIVE
Substantial relief — conventionally around 80 percent or more — lasting roughly as long as the anesthetic should, and returning as it wears off. That pattern identifies the facets at those levels as the pain generator and makes radiofrequency neurotomy the logical next step.
A PARTIAL RESPONSE
Meaningful but incomplete relief usually means the facets are contributing alongside something else — commonly the sacroiliac joint or a disc. That is useful information rather than a failed test, and it usually redirects to testing the second structure rather than to treating the first.
A CLEAR NEGATIVE
No change. The facets at those levels are not generating your pain, and any plan built on the assumption that they were has just been prevented. This is the outcome patients find most disappointing and the one that most often saves them from a procedure that would not have worked.
Why we usually do it twice
A single block has a meaningful false-positive rate. Placebo response is real, anesthetic spreads, and people want to feel better. A confirmatory block on a separate day, ideally with a different-duration agent, substantially raises the odds that a positive result is real.
That second appointment is inconvenient and we ask for it anyway, because the treatment it authorizes is worth being right about. This is the point in the pathway where cutting a corner produces a neurotomy that was never going to help, and then a patient described as having failed radiofrequency ablation.
Why there is no steroid in a diagnostic block. Steroid would make the relief last longer, which sounds better and destroys the test — the whole logic depends on the relief ending when the anesthetic ends. If you have been given a “facet injection” with steroid and told it was diagnostic, those were two different procedures wearing the same name.
Risks, stated plainly
This is a low-risk outpatient procedure and it is not a no-risk one. Expect the puncture sites to ache for a day or two. Anesthetic occasionally tracks further than intended and leaves a numb or heavy leg for a few hours, which clears as the drug does. Bleeding, infection and nerve injury are uncommon. Steroid is not used, so the metabolic effects that come with it do not apply here — which matters more in this population than it is usually given credit for.
If you take an anticoagulant, tell us before the appointment rather than on the day. Most are manageable with planning and some require a pause that has to be arranged with whoever prescribed it.
What we need from you
Honest numbers. The most common way this test fails is not technical — it is a patient who wants the answer to be yes, reports relief generously, and ends up with a treatment aimed at the wrong structure. A negative block reported accurately is worth more to you than a positive one reported hopefully.
The second thing is movement. Get up and do the thing that hurts. A block assessed at rest measures very little, because a facet joint under no load was not going to hurt anyway.
Common questions
Does it hurt?
The skin anesthetic stings briefly. After that most people describe pressure rather than pain. It is a short procedure and you walk out of it.
There is no scan that finds it. That is why you still do not have an answer. goes through it in detail.
Can I drive afterward?
We ask you to arrange a driver. Sedation is not routinely used, but leg numbness from anesthetic spread is possible and it is not something to discover on the highway.
The detail is in Durable relief for facet pain, if the right nerves were identified first..
What if it only helps for a few hours?
That is exactly what is supposed to happen. The relief ending as the anesthetic ends is what makes the result interpretable.
It does not shrink the disc. It buys you the window in which the disc shrinks itself. explains what that looks like.
Is this the same as a facet joint injection?
No. A facet joint injection places steroid inside the joint capsule and is aimed at treatment. A medial branch block places anesthetic on the nerves outside the joint and is aimed at diagnosis. They are used for different purposes and confusing them is common.
The mechanism is covered in A joint this deep cannot be injected by feel. If it was not imaged, it was not necessarily treated..
What if both blocks are positive?
Then you have a confirmed diagnosis, which is more than most people with years of back pain have ever been given, and a clear next step in radiofrequency neurotomy.
Related reading
- Lumbar facet syndrome
- Radiofrequency neurotomy
- What your MRI actually showed
- What happens at the first visit
- Pain after back surgery
A test that can come back negative is the only kind worth doing
If nobody has blocked your facets, nobody has tested them, and every plan built on that assumption is unverified. We will tell you which levels we suspect and why before we go near them.
12174 Natural Bridge Rd, Suite 301
St. Louis, MO 63044
At DePaul Hospital on Natural Bridge Road, inside the I-270 and I-70 interchange, on the west side of the airport.
Sources
- Wahezi SE et al. Lumbar Medial Branch Block Volume-Dependent Dispersion Patterns as a Predictor for Ablation Success: A Cadaveric Study. PM & R : the journal of injury, function, and rehabilitation, 2018. PubMed 29174073
- Roy C et al. Correlation of lumbar medial branch neurotomy results with diagnostic medial branch block cut off values: a letter to the editor. Pain medicine (Malden, Mass.), 2013. PubMed 23565823
- Manchikanti L et al. Comprehensive Evidence-Based Guidelines for Facet Joint Interventions in the Management of Chronic Spinal Pain: American Society of Interventional Pain Physicians (ASIPP) Guidelines Facet Joint Interventions 2020 Guidelines. Pain physician, 2020. PubMed 32503359
- Sherwood D et al. Lumbar medial branch block progression to radiofrequency neurotomy: A retrospective audit of clinical practice. Interventional pain medicine, 2022. PubMed 39238824