Nerve blocks: what they are, how they're done and what to expect

If you are considering interventional treatment for pain, the term "nerve block" is very likely to come up in the conversation. I want to explain clearly what nerve blocks are, how they are performed, what results to expect and, above all, in which situations they are genuinely useful.

When I talk about nerve blocks with patients, the first thing I clarify is that they are not one single thing. "Block" is a generic word that covers very different techniques with very different goals: some help diagnose where the pain is coming from, others treat it for an extended period, and others support a rehabilitation program that couldn't move forward without that relief. Many patients arrive thinking it's a single injection that "numbs a nerve" and makes the problem go away. The reality is more interesting and, above all, more strategic.

What a nerve block is

A nerve block is a procedure in which medication (typically a local anesthetic, alone or combined with a corticosteroid) is placed near a specific nerve or structure, with the goal of:

• Relieving pain directly.
• Reducing local inflammation when that is the cause of the pain.
• Diagnosing the exact source of the pain when there is uncertainty.
• Modulating the mechanisms of chronic pain.

The idea is simple: instead of medicating the whole body with oral pain relievers — with all the side effects that implies — the medication is delivered to the exact spot where the problem originates. It's like going straight to the source instead of flooding everything around it.

One nuance I repeat often: what defines the quality of a nerve block is not the drug being injected but the anatomical precision. Today we work with ultrasound or fluoroscopic guidance to reach exactly the target we want: a nerve root, a medial branch, a peripheral nerve, a joint. That level of precision is what separates a modern nerve block from a blind injection. And it's also what explains why results can vary so much from one center to another, even when the procedure has the same name on paper.

The most common types in pain medicine

Joint blocks

A specific joint is injected with anti-inflammatory medication. The most common are:

• Lumbar or cervical facet joint block: for pain coming from the facet joints of the spine.
• Sacroiliac joint block: for pain from the sacroiliac joint.
• Peripheral joint injections: shoulder, knee, hip, elbow.

Epidural blocks

Medication is placed in the epidural space of the spine (lumbar, cervical or caudal). Indicated for herniated discs, sciatica, spinal stenosis and other conditions affecting the nerve roots. It is one of the most widely used techniques in pain medicine, and one with the strongest evidence base.

Peripheral nerve blocks

These target specific nerves in the body: the greater occipital nerve (for headaches), the suprascapular nerve (for the shoulder), the genicular nerves (for the knee), the pudendal nerve (for pelvic pain), among many others.

Sympathetic blocks

These act on the autonomic nervous system. Indicated for complex neuropathic pain, complex regional pain syndrome and some chronic visceral pain conditions. Examples: stellate ganglion block, celiac plexus block, lumbar sympathetic blocks.

Trigger point injections

Local injection of hyperirritable myofascial points that generate pain. Used for myofascial pain syndromes.

How a nerve block is performed

The typical procedure follows these steps:

1. Preparation: the patient is positioned appropriately (face down, sitting, or on their side depending on the block). The skin is prepared with antiseptic.
2. Local anesthesia: anesthetic is injected into the skin to minimize discomfort from the needle.
3. Image guidance: ultrasound or fluoroscopy (real-time X-ray) is used to reach the exact site with precision. This is what distinguishes a well-performed, modern nerve block.
4. Confirmation: in some cases a small volume of contrast dye or anesthetic is injected to confirm correct positioning before delivering the main medication.
5. Injection of the medication: typically a local anesthetic with or without a corticosteroid, depending on the indication.
6. Recovery: the patient remains under observation for 15 to 30 minutes before walking out.

The total duration of the procedure ranges from 15 to 45 minutes depending on the type. It is an outpatient procedure: patients go home the same day.

Does it hurt?

It's the most common question. The honest answer: the discomfort is usually mild and well tolerated. The local anesthetic given beforehand minimizes needle pain, and image guidance itself allows us to work with the least invasiveness possible. Most patients describe the experience as "milder than I expected."

What results to expect

This varies with the type of block and the indication:

• Immediate effect: the local anesthetic produces relief within minutes, lasting hours. This is useful both therapeutically and to confirm the diagnosis.
• Sustained effect: the corticosteroid (when used) takes effect over the following days and can last weeks to months.
• Individual variability: some patients respond very well and others less so. The response to a block provides useful clinical information even when it doesn't last as long.

In many cases, the block is paired with targeted physical therapy to enhance and prolong its effect. The idea is not just to "mask the pain" but to use the window of relief to work on the mechanical, postural and muscular causes of the condition.

Risks and considerations

Image-guided nerve blocks, performed by trained specialists, are safe procedures. Complications are uncommon, but it's worth knowing them:

• Minor bleeding at the injection site, temporary local soreness.
• Very low risk of infection.
• Temporary corticosteroid effects (mild blood sugar elevation in people with diabetes, facial flushing).
• Complications specific to each type of block, which are explained to you in detail before the procedure.

Patients on blood thinners, with active infections or with certain medical conditions may have temporary or relative contraindications, which are assessed case by case.

My criteria for recommending a nerve block come down to three things: the clinical diagnosis must point clearly to an anatomical target, the patient must have completed a reasonable course of conservative treatment, and the block must fit within a broader plan. I don't order isolated, decontextualized blocks as if they were a treatment in themselves. I use them when they provide information that changes management, or when they open a window of relief that allows physical therapy and postural retraining to move forward. If a block isn't part of a plan, it tends to offer short-lived relief that ends up disappointing.

When a nerve block makes sense

Broadly speaking, nerve blocks are indicated when:

• Medical treatment isn't controlling the pain.
• The pain has a clear anatomical location that can be targeted.
• There is significant functional limitation.
• The goal is to confirm the source of the pain before considering surgery or more invasive treatments.

The decision about which block, when, and with what expectations is made during the consultation, based on an evaluation of your particular case. Well indicated and well performed, a nerve block can make a real difference in quality of life.

What defines the long-term success of a nerve block is not how many days of relief the patient felt, but what the patient was able to do with that relief. When someone uses that window to build strength, to start moving again, to correct habits, the result holds up long beyond the pharmacological effect. That's why I always tell them the same thing: the block opens a door, but you have to walk through it. My job is to choose well — when, where and what for; the patient's job is to seize that opportunity to build real change in their daily life.

Dr. Mauricio Casarsa

Anesthesiologist, specialist in Pain Medicine and Interventional Pain Management. Postgraduate training at UBA (Fundación Dolor) and UNLP (CAIDBA). Staff physician at Hospital Alemán, Buenos Aires.

MN 137756 · San Isidro · Villa Urquiza