Why can’t a scan show whether a facet joint is causing my pain?

Each spinal level carries two small joints at the back, one on either side. By sixty, almost everyone’s show wear on a CT scan. In the Framingham community sample, facet joint osteoarthritis was common in every age group and close to universal in the oldest. Its presence did not predict who had back pain. So a radiologist writing “facet arthropathy” has told you what your spine looks like, not what is hurting. The only way to know whether a given joint is the source is to switch off its nerve supply. Then see whether the pain goes with it.

Each facet joint is fed by two medial branches, one from its own level and one from above. They are small. They run over bony landmarks we can predict. And they can be bathed in a drop of local anesthetic under X-ray. If the joint was the source, the pain drops sharply while the anesthetic works. It comes back on schedule when it wears off. If the joint was innocent, nothing changes. That is a useful answer too.

What should I do after a medial branch block?

A block you spend lying on the couch tells you almost nothing. Facet pain is mechanical. The joint hurts when it is loaded in extension and rotation (arching and twisting). That is the reach up to the top shelf, the twist to look behind a forklift, the arch of the back under a welding hood, the climb down from a cab. Before the block, we ask you exactly which movements light it up. After the block, we ask you to go do a controlled version of them. Then you record, hour by hour, what percent of the usual pain is there. That written record, checked against the known duration of the anesthetic, is the result. We are not asking whether you feel better. We are asking whether the specific pain that stops you working was switched off by numbing two specific nerves.

Three things make a joint hurt more than its X-ray deserves. The capsule is packed with mechanoreceptors (touch and stretch sensors) that grow touchy once the cartilage thins. Metabolic inflammation, the low-grade body-wide kind that travels with insulin resistance, lowers their firing threshold. It also primes the spinal cord to amplify the signal. And the load: a job that arches the lumbar spine a few hundred times a shift. Or a night schedule that steals the deep sleep in which pain thresholds reset. A positive block identifies the joint. It does nothing about the other two. That is why the block is the start of a plan, not the plan.

Can I drive home to the Metro East after a medial branch block?

For a Metro East patient, the test is running while you cross the river. Short-acting anesthetic works for one to two hours, longer-acting for several. The first hour is the one that matters most. With roads clear and no traffic figured in, Granite City is about 25 minutes from the office, Collinsville about 40, Belleville about 40. There is no sedation, so you can drive, but a passenger who writes the diary while you sit, bend and climb in and out of the car turns the commute into data. Coming alone, you rehearse the movements in the parking lot before you leave and fill in the sheet at each stop.

How do you know if a medial branch block worked?

The two-block rule has a trade-off, and we will state it. A 2010 randomized trial in Anesthesiology compared sending patients to radiofrequency ablation after zero, one or two positive blocks. It found that skipping the blocks produced more successful ablations per patient treated, because fewer people were screened out. It also burned nerves that were never the problem, in patients whose pain was never facet. The 2020 multispecialty consensus guidelines and the ASIPP guidelines of the same year keep the diagnostic block as the gate. So does this practice. A burned nerve in the wrong patient is a wasted year and a wrong diagnosis.

When it is an Illinois work injury

Facet pain after a lifting or twisting injury at work is common. An Illinois claim runs through the Illinois Workers’ Compensation Commission. A documented, image-guided, timed block with a written diary is objective evidence of where the pain comes from. It reads differently in a file than “chronic low back pain.” Under 820 ILCS 305/8(a) an injured Illinois worker generally chooses their own physician, within the two-choice chain-of-referral limit and subject to any approved preferred provider program the employer runs. How that applies to your claim is a question for an attorney or the IWCC; what we can do is make the record accurate. Our page for patients injured at work covers the rest.

What happens during a medial branch block?

Frequently asked questions

Is this the same as a facet joint injection?

A block numbs the nerves outside the joint to test it. A facet joint injection puts steroid inside the joint to treat a flare. One is a question and the other is a treatment, and they are read completely differently.

What counts as a positive result?

Most of the provoked pain gone for about as long as the anesthetic lasts, and then back. How we turn that diary into a decision is the subject of what a diagnostic block tells you.

Why do I need it twice before an ablation?

Because a single block is fooled by expectation and by the natural rise and fall of a flare, and the thing it gates, radiofrequency ablation, disables a nerve for most of a year. Two agreeing blocks on separate days are what make that a safe bet.

Can I drive myself back to Illinois?

There is no sedation and the anesthetic stays on the nerves at the back of the spine, so most patients drive, though a passenger keeping the diary makes the trip more useful; see driving home after a spine injection.

Does the same test work for neck pain and headaches?

The cervical (neck) facets have their own medial branches. The upper ones send pain into the back of the head. So the same logic applies, with the provocation being turning and looking up. The facet joint pain page covers both regions.

How long does a medial branch block last?

The numbing lasts only as long as the anesthetic: one to two hours for a short-acting drug and several hours for a longer-acting one. That short window is on purpose, because the test is whether your usual pain disappears and then returns on schedule. Relief that lasts for weeks is not the anesthetic at work. That is why a single block is never trusted on its own.

What happens next if a medial branch block doesn’t work?

If nothing changes during the anesthetic window, the joint that was numbed is not the source of your pain. That is still a useful answer. One suspect is ruled out, and nobody burns a nerve that was never the problem. The search then moves to the other likely sources, such as the disc, the sacroiliac joint or the hip.

Is it worth getting a medial branch block?

For pain that may come from a facet joint, yes. By sixty, almost everyone’s facet joints show wear on a CT scan. In the Framingham community sample, that wear did not predict who had back pain. The block is the only way to learn whether a given joint is the one hurting. It is the gate this practice uses before radiofrequency ablation, so a nerve is never burned on a hunch.

Related reading

• Facet joint pain
• Radiofrequency ablation
• Facet joint injection
• What a diagnostic block tells you
• Injured at work in Illinois