What is a diagnostic nerve block?

Most of what a spine can hurt with does not show on a scan. A facet joint that has been grinding for years looks the same on MRI as one that has never hurt. A sacroiliac joint looks like nothing at all. So the diagnosis is made by switching a structure off and seeing what happens. A small volume of local anesthetic is placed under fluoroscopy (live X-ray) on the nerves that carry feeling from that one joint. For the next few hours, that joint cannot report pain. Say the pain you came in with drops by most of its strength for the length of time that anesthetic should last. Then the joint was the source. If nothing changes, it was not, and that is an answer too.

The block is the test, not the treatment. It is meant to wear off. Relief that lasts an afternoon and then returns is the result working exactly as designed. That is why nobody should judge a block by whether they felt better the next week.

Why is one diagnostic block not enough?

The original prevalence studies of lumbar facet pain compared a single block with a second, controlled one. About 38 percent of the single blocks that looked positive turned out to be false positives. The reasons are ordinary. The anesthetic spreads to a neighbor. The pain happened to be quieter that day. The expectation of relief produced some. Every multispecialty guideline since has required two concordant blocks (two that match), on separate days, before the diagnosis is made or a radiofrequency ablation is offered. Two blocks cost a second drive from the Metro East. A radiofrequency procedure on the wrong nerve costs more than that.

What should you record after a diagnostic nerve block?

• Pain intensity before the block, on the 0 to 10 scale, doing the movement that usually brings it on.
• The same score at 30 minutes, one hour, two hours, four hours and six hours, doing the same movement each time.
• What you could do that you normally cannot: turn to check a mirror, climb the stairs, sit through the drive.
• When the pain came back, and whether it came back to the same place.

No blood pressure cuff or heart rate monitor can replace this. A prospective study looked for changes in vital signs that might predict which patients would respond to facet blocks and radiofrequency denervation. It found none worth using. The tool is your own report, at set times, doing a set movement. That is why the diary is handed to you before the needle, and why the drive home is counted as data rather than dead time.

How do you know if a diagnostic block worked?

What should you not do after a nerve block?

Blocks here are done awake under local anesthetic with no sedation, so most people drive themselves home; the exception is temporary numbness or weakness in a leg after some lumbar blocks, which is checked before you leave and which is one of the reasons the drive back over the river is discussed on the driving home page. Do not take extra pain medicine on the day, because it blurs the result. Do the movement that hurts, on purpose, at each time point. And do not decide on the drive that the block failed because the pain is back at hour five; that is the anesthetic ending, which is what it is for.

Frequently asked questions

What does it mean if the block only lasted a few hours?

That the test worked. The anesthetic was meant to wear off, and relief for as long as it should last is a positive result. The medial branch block page describes this in detail.

Why do I need two blocks before an ablation?

Because about a third of single facet blocks that look positive are false positives. Two matching results on separate days are what make radiofrequency ablation a treatment aimed at a confirmed target.

Can I drive home after a diagnostic block?

Usually, since there is no sedation; temporary leg numbness after some lumbar blocks is the exception, and the plan for it is on the driving home page.

What if the block did nothing?

The structure is ruled out, and the exam moves on, often to the sacroiliac joint or the hip. That is a shorter route to the right diagnosis than a treatment that would have missed.

Is a diagnostic block useful in an injury claim?

It gives a percentage and a length of relief, recorded twice on different days. That is the closest thing to an objective finding in this field. It is explained for counsel on the attorneys page.

How long does a diagnostic nerve block last?

A few hours, by design. The local anesthetic switches the targeted nerves off for about as long as that drug lasts. That is why the diary runs at 30 minutes and at one, two, four and six hours. Pain coming back at hour five is the anesthetic ending, not the block failing. Relief that lasts an afternoon and then returns is the test working exactly as intended.

Are you awake for a diagnostic nerve block?

Yes. Blocks here are done awake under local anesthetic with no sedation, and the needle is placed under fluoroscopy. You do the movement that usually hurts before the block and again at each time point afterward. That is because your own report is the result. With no sedation, most people drive themselves home; temporary leg numbness after some lumbar blocks is checked before you leave.

Does a diagnostic nerve block treat the pain?

Not for long. A diagnostic block with local anesthetic is a test, not a treatment, and it is meant to wear off. Its job is to confirm which structure is causing the pain. When two blocks on separate days both give clear relief, the next step is a procedure aimed at that confirmed target, such as radiofrequency ablation. Its relief was measured in many months in the original studies.

Why can’t an MRI show which joint is causing the pain?

Because most of what a spine can hurt with does not show on a scan. A facet joint that has been grinding for years looks the same on MRI as one that has never hurt. A sacroiliac joint looks like nothing at all. Switching one structure off with anesthetic and recording what happens to your pain is how the source is actually confirmed.

Where can I get a nerve block near Belleville, IL?

Blocks for Belleville patients are placed at the Woodson Road clinic beside Lambert Airport, about 40 minutes away with clear roads. The consultation that decides which block you need can be booked at the Illinois office in Troy, and the follow-up about your diary can be a phone or video call, so the bridge is crossed for the needle and not for the talk. Ask for the block by its target, not by the words “nerve block”: a medial branch block tests a facet joint, a sympathetic block tests a limb that may have CRPS, and the two answer different questions. Learn more: getting back over the river after a block.

Related reading

• Medial branch block
• Radiofrequency ablation
• Facet joint pain
• Sacroiliac joint injection
• Driving home after a spine injection