A short, targeted diagnostic injection that answers one question very precisely: are your facet joints the source of your pain?
A medial branch block — usually shortened to MBB — is a diagnostic injection. We place a small amount of local anesthetic onto the tiny medial branch nerves that carry pain signals from your facet joints — the small paired joints in the back of your spine that guide and limit motion. If numbing those nerves dramatically reduces your usual pain, we've identified the facet joints as the source, and you become a candidate for a longer-lasting treatment called radiofrequency ablation (RFA).
It's important to understand up front that an MBB is not meant to treat your pain — it's meant to answer a question. The anesthetic wears off in a matter of hours. What matters is what happens during those hours: how much your usual pain improves, and whether activities that normally hurt feel different. That information drives the next step in your care.
An MBB is most useful for patients with chronic axial back or neck pain — meaning pain that stays close to the spine rather than radiating down an arm or leg — when the pattern fits a facet-joint problem and conservative care hasn't fixed it.
An MBB is generally not the right test if your dominant pain is radicular (radiating down an arm or leg in a nerve pattern — that points toward a disc or nerve root problem instead), if there's active infection, uncontrolled bleeding risk, or if you can't reliably report your pain response during the post-procedure window.
We confirm your current pain level on a 0–10 scale and what activities normally make it worse. You'll lie face-down on the fluoroscopy table.
The skin over the target levels is cleaned and numbed with a small amount of local anesthetic — this is the part you actually feel.
Using fluoroscopy, we place very thin needles onto the medial branch nerves at the levels we're testing (usually two or three on each side) and deliver a small volume of anesthetic to each.
Over the next 4–6 hours, you'll rate your pain at regular intervals and ideally do an activity that normally provokes it. This is the actual data we use.
The block itself takes about 30 minutes. There's no sedation, so you can drive yourself home. Mild soreness at the injection sites is normal for a day or two and responds to ice and over-the-counter medication. Because the anesthetic is short-acting, any pain relief you experience will fade within a few hours — that's expected, not a failure.
To reduce the risk of a false-positive result, most patients undergo two separate blocks on different days, sometimes with anesthetics of different durations. If both blocks reliably reproduce substantial relief — typically more than 50 to 80 percent — that strongly supports facet-mediated pain and makes you a candidate for radiofrequency ablation, which can give six to twelve months or more of relief. If the blocks don't help, we've still learned something valuable: the facets aren't the problem, and we redirect your evaluation toward another source.
MBBs are among the lower-risk spinal procedures we perform. Most patients have, at most, mild soreness for a day or two. Less common effects include a temporary increase in pain, small bruising, and rarely, infection or bleeding. If the anesthetic spreads onto a nearby motor nerve, you may notice a few hours of leg or arm weakness — uncommon and self-resolving, but a reason to arrange help with stairs if you live alone.
KeyTone Medical is out of network with all commercial health insurance plans, so this procedure is self-pay, with the cost discussed before anything is scheduled. Many plans reimburse part of the cost of medically necessary care performed out of network — on request we provide a superbill, an itemized and coded receipt, for you to submit to your insurer under your plan's guidelines.
The medication we use is a local anesthetic — the same family as the numbing medicine your dentist uses — and it wears off in hours. We're not trying to fix anything with the block. We're using a short, well-targeted numbing test to find out which structures are sending the pain signal. That answer determines what the actual treatment should be.
A single positive block can occasionally be misleading — placebo effect, anesthetic spread to nearby tissue, or a coincidentally good pain day can all create a false positive. Doing a confirmatory second block on a separate day, and watching whether the relief reproduces, makes the diagnosis much more reliable before committing to a longer procedure like RFA.
If your pain reliably drops substantially during the anesthetic window — typically more than 50 to 80 percent — and the result reproduces on a confirmatory block, we'll discuss radiofrequency ablation. RFA uses heat to interrupt those same medial branch nerves for a much longer time, usually six to twelve months or more.
That's still useful information. A negative block means the facet joints probably aren't the main pain generator, and we'd avoid putting you through RFA that wouldn't help. We re-evaluate and look at other potential sources — disc, SI joint, nerve root, muscular — based on your exam and imaging.
A facet joint injection places anti-inflammatory steroid directly into the joint itself and is intended to be therapeutic. A medial branch block places only anesthetic onto the nerves supplying the joint and is intended to be diagnostic. They sit near each other anatomically but answer different questions and serve different purposes.
Authoritative references on this topic, for patients who want to read further. These are educational resources, not medical advice.
Educational information only. This page describes medial branch blocks in general terms. Whether an MBB is appropriate for you depends on your history, exam, imaging, and treatment goals. The risks, benefits, alternatives, and expected results will be discussed in detail at your visit.
