I see this question in my practice every week: “Dr. Schmidt, I had this injection in my back last week — was that the burn?” No. Almost certainly it was the test that comes before the burn, and the difference between the two is the difference between a diagnostic step and a therapeutic procedure. The honest version is this — the medial branch block (MBB) is a temporary test that tells us whether your facet joints are the pain generator, and the radiofrequency ablation (RFA) is the durable treatment that follows when the test is positive. As a triple board-certified pain medicine specialist (ABA Anesthesiology, ABA Pain Medicine, ABIPP), I do both procedures regularly in my Hoffman Estates practice, and this is the page I wish every patient had read before their first injection.
The 90-second answer
A medial branch block is a small, image-guided injection of local anesthetic only — sometimes a tiny amount of steroid for the contrast injection, but mostly just numbing medicine — placed at the small medial branch nerves that carry pain from your facet joints. It is a test. Relief lasts hours to a day or two. If you get good relief during the numb-window, your facet joints are confirmed as the pain source. A radiofrequency ablation, by contrast, is a therapy. Using a similar needle path, I deliver controlled radiofrequency heat at each medial branch nerve to create a small, precise thermal lesion that interrupts that nerve’s ability to carry pain signals. The result, in the right patient, is 6 to 18 months of meaningful relief. The MBB is the gateway. The RFA is the destination. You usually need two positive MBBs before we proceed to RFA.
What a medial branch block actually does
Your spinal facet joints are the small paired joints at the back of each vertebra that let you bend, twist, and extend. Each facet joint is innervated by tiny sensory nerves called medial branches of the dorsal rami — purely sensory at the facet level, meaning they carry pain information but do not control any major muscle. That anatomical fact is what makes the entire protocol possible.
During an MBB, under live fluoroscopic guidance, I place a thin spinal needle precisely against the bony landmark where each medial branch crosses, and inject a small volume of local anesthetic (typically bupivacaine or lidocaine) directly onto that nerve. For a few hours — sometimes up to 24–48 hours — that nerve cannot transmit signals. If the facet joints were indeed the source of your pain, your pain melts. If they weren’t, the injection won’t help much, and that’s its own answer.
A typical lumbar MBB targets two adjacent levels to cover one facet joint, because every facet joint is innervated by two medial branches — one from the level above, one from its own level. For example, to test the right L4-L5 facet, I block the L3 medial branch and the L4 medial branch. The same logic applies in the cervical and thoracic spine, with slightly different anatomic targets.
The MBB takes 15–25 minutes, is done under local with light sedation if needed, and you leave the office with a pain diary in hand. Your job for the next 4–8 hours is to track how much your pain changes, and to do the movements that normally hurt — bending, rotating, standing, walking — so we can see if the diagnostic block actually changed your day. The pain diary is not optional. It is the data the entire decision rests on.
What a radiofrequency ablation actually does
A radiofrequency ablation of the medial branch nerves uses a specialized RF probe — placed under the same fluoroscopic guidance, often along an almost-identical needle path as the MBB — to deliver controlled radiofrequency current to each target nerve. The probe heats its tip to a precise temperature (typically 80°C for 90 seconds per lesion) to create a small, well-controlled thermal lesion that interrupts that medial branch’s ability to carry pain signals. Cooled and pulsed RF variants exist; conventional thermal RFA is the standard for facet RFA. The complete procedural detail lives on the radiofrequency ablation page.
The medial branches do eventually regenerate over months — that is biology, not failure — which is why the relief is durable but not permanent. Most patients get 6 to 18 months of meaningful relief from a well-performed RFA, and re-RFA at intervals is part of the standard protocol. I tell patients to think of RFA the way they think of cataract surgery or a dental crown: a real intervention, with a real shelf life, that can be repeated when the relief fades.
The RFA itself takes 30–60 minutes, is done under local with light-to-moderate sedation, and patients walk out the same day. Recovery is typically 3–10 days of mild post-procedure soreness over the treated area — sometimes called “RF burn” by patients, though it’s really a small, predictable inflammatory response from the lesioning — followed by the gradual onset of pain relief over 2–4 weeks as the nerves stop firing.
Side-by-side: Medial Branch Block vs Radiofrequency Ablation
| Feature | Medial Branch Block (MBB) | Radiofrequency Ablation (RFA) |
|---|---|---|
| Purpose | Diagnostic test — confirms facet joints as pain source | Therapeutic procedure — durable relief of facet pain |
| What is injected/applied | Local anesthetic (± tiny steroid for contrast) at each medial branch | Radiofrequency thermal energy at each medial branch |
| Mechanism | Temporary anesthetic block of the medial branch nerve | Controlled thermal lesion that interrupts the medial branch nerve |
| Duration of effect | Hours to a day or two | 6 to 18 months typical; can be repeated |
| Procedure time | 15–25 minutes | 30–60 minutes |
| Anesthesia | Local + light sedation if needed | Local + light-to-moderate sedation |
| Imaging guidance | Live fluoroscopy | Live fluoroscopy |
| Same anatomic target? | Yes — both target the medial branches of the dorsal rami at the same spinal levels | Yes |
| Pre-procedure prep | Hold sedating medications per office instructions; arrange a driver if sedated | Hold blood thinners per office instructions; arrange a driver |
| Post-procedure expectations | Track pain relief during the anesthetic window (4–48 hours). Bring the pain diary back. | Mild soreness over treated area for several days. Gradual onset of relief over 2–4 weeks. |
| How many needed before next step? | Typically two positive MBBs (separated in time, with concordant relief) before proceeding to RFA — payer-driven and evidence-based | One RFA per painful level set. Repeat RFA when relief fades. |
| Insurance coverage | Universally covered when indicated and documented | Universally covered after positive MBB criteria are met and documented |
| Risks | Very low: bruising, transient soreness, rare infection, very rare dural puncture | Very low: post-procedure soreness, transient numbness, rare dysesthesia, very rare motor effect if nerve target is incorrect |
| What it does NOT do | Does not give durable relief. Does not treat the pain. | Does not heal the facet joint. Does not address other pain generators. |
| What a positive result tells us | Your facet joints at the tested levels are the pain source — proceed to RFA | Your facet pain at those levels should be substantially reduced for many months |
| What a negative result tells us | Facet joints are NOT the dominant source — look elsewhere | Either anatomic targeting issue or pain source has shifted — re-evaluate |
How I decide what to offer — and why the order matters
The MBB-then-RFA protocol is not a billing trick. It is the protocol that protects you from a procedure that won’t help you.
Facet pain is common. By some estimates, facet joints contribute to 15–45% of chronic low back pain and an even higher proportion of chronic neck pain. But MRI and CT alone are unreliable for diagnosing facet pain — most adults over 40 have some facet arthropathy on imaging, and most of them are not in pain from those facets. The clinical exam helps (pain worse with extension and rotation, worse standing than sitting, tenderness over the facets), but the exam alone is not specific enough to commit a patient to a thermal procedure. The MBB is the diagnostic test that closes that gap.
Why two MBBs and not one? Because a single MBB has a meaningful false-positive rate. Patients can get short-term relief from a single injection for reasons that aren’t really about the facet joint — placebo effect, systemic uptake of local anesthetic, regression to the mean on a bad day. The literature has been clear for years: dual concordant blocks (two separate MBBs, each showing the expected pattern of relief) substantially reduce false positives and improve the probability that RFA will work [Bogduk, Pain Med 2008, PMID 18564999]. Most commercial payers and Medicare local coverage determinations now require two positive MBBs before approving RFA, and that’s a good policy — I’d require it even if they didn’t.
What does “positive” mean? I look for ≥80% relief during the anesthetic window and concordant response — meaning the relief tracks your usual pain pattern, not just a vague “I feel better.” Some payers accept 50% as the threshold, but the higher threshold gives me a more confident RFA recommendation. The pain diary tells me what I need.
A real example. A 58-year-old patient came in with two years of axial low back pain, worse with extension, worse standing, no leg radiation, normal neurologic exam. MRI showed moderate multilevel facet arthropathy at L4-L5 and L5-S1, no significant stenosis, no instability. He’d had a course of PT and an epidural that didn’t help much — which itself was a clue, because epidurals don’t reliably treat facet pain. Plan: bilateral L4-L5 and L5-S1 MBBs. First block: 85% relief for about six hours, tracked in his diary, with extension and rotation no longer triggering pain. Second block, three weeks later: 90% relief for about eight hours. Two positive concordant blocks. We then proceeded to bilateral lumbar medial branch RFA at L3, L4, and L5 medial branches (to cover L4-L5 and L5-S1 facets). At his three-month follow-up, he was at about 70% relief, sleeping through the night, and walking his neighborhood again. We re-RFA about every 12 months now.
When neither of these is the right next step
Even with a textbook facet exam, the RFA pathway isn’t always right.
If your pain has a strong radicular component — burning down one leg, weakness, numbness in a dermatomal pattern — the facets aren’t the dominant problem, and we should be thinking about radicular pain, stenosis, or a neuropathic process (and possibly neuromodulation downstream). If imaging shows significant lumbar spinal stenosis with neurogenic claudication, the facets may be background noise — the dominant problem is central canal compression (see MILD vs laminectomy vs epidural). If the MRI shows Modic Type 1 endplate changes and the pain is deep central low back pain worse with sitting and forward flexion, the pain may be vertebrogenic (basivertebral nerve mediated) and a basivertebral nerve ablation may be the better procedure than a facet RFA. And if your knee pain is the issue, the genicular nerve protocol — diagnostic genicular nerve block followed by genicular RFA — is the same logic applied to the knee.
The point is the same throughout pain medicine: match the diagnostic block to the suspected pain generator, then match the ablation to the positive block. The medial branch block and the facet RFA are one example of that two-step principle. They are not the only one.
FAQ
I just had a medial branch block. When will I know if it “worked”? You’ll know within the first few hours. The local anesthetic kicks in within 15–30 minutes and lasts roughly 4–24 hours depending on the agent used. During that window, do the movements that usually hurt and track your pain in the diary the office gave you. If your usual back pain is dramatically better during that window, the block worked diagnostically — your facets are the pain source. If the pain comes back the next day, that is expected. The block is a test, not a cure.
Why do I need two medial branch blocks instead of just one? A single positive MBB has a real false-positive rate. Two concordant positive blocks substantially reduce the chance that we proceed to RFA on a patient who won’t benefit. Most payers require it, but more importantly, two blocks make my recommendation more honest. I’d rather do a careful diagnostic workup than rush to a procedure that doesn’t help.
How long does an RFA last? Typically 6 to 18 months of meaningful relief, with some patients getting two years or more. The medial branches regenerate over time — that’s normal biology — and the relief gradually fades. When it fades to the point where pain is meaningfully back, we repeat the RFA. Re-RFA is not a failure; it is the standard protocol.
Is the RFA painful? The procedure itself is done under local anesthesia with light sedation if you want it; most patients feel pressure and warmth, not sharp pain. Afterward, you’ll have several days of mild-to-moderate soreness over the treated area — sometimes called “RF burn” — that resolves with ice, gentle movement, and time. The actual pain relief begins to build over the following 2–4 weeks as the treated nerves stop firing.
Can I have an RFA without first having a medial branch block? Almost never, and not in my practice. Skipping the diagnostic step risks doing a thermal procedure on someone whose pain wasn’t coming from the facets — meaning they get the post-procedure soreness of the RFA without the benefit. Insurers also typically deny RFA without a documented positive MBB. The two-step protocol is the protocol.
Will the RFA damage anything important? The medial branches at the facet level are purely sensory — they don’t control any major muscle, and they don’t carry sensation from the skin or limbs. That is exactly why this procedure is so well-tolerated. Rare side effects include a few weeks of localized numbness or dysesthesia, occasional flare of soreness, and very rarely, a transient unusual sensation. Properly performed lumbar facet RFA does not weaken your back.
If you’ve just had your first medial branch block — here’s the next step
If you’ve just had a medial branch block and you’re sitting at home wondering what comes next, the answer is simple. Track your pain carefully for the next 24–48 hours, bring the diary back to the office, and we make the decision together about whether a second confirmatory block — and then a radiofrequency ablation — is the right next move. If you haven’t had any of this done yet and you’re trying to understand whether facet pain is even the right diagnosis, that’s exactly the conversation to have in clinic. Call my Hoffman Estates office at (847) 981-3630 to schedule a consultation, or read more on the radiofrequency ablation page.