SI joint injections

The sacroiliac (SI) joints connect the sacrum, a triangle-shaped bone at the base of the spine, to the two large hip bones. There is one on each side, at the back of the pelvis. These joints move only a little. Strong bands of tissue called ligaments hold them firmly in place.

Pain from an SI joint is usually felt low in the back or in the buttock. It can spread into the thigh, and sometimes below the knee or into the groin. The joint itself or the ligaments around it can be the source of pain.

An SI joint injection places numbing medicine, often mixed with a steroid, into the joint. Some clinicians place medicine just around the joint, in the ligaments behind it, instead of or as well as inside it.

The injection is guided by imaging, usually a live x-ray (fluoroscopy), and sometimes CT or ultrasound. Imaging matters. In one study, only about 1 in 5 injections done by feel alone reached the inside of the joint.

Specialists in pain medicine, physical medicine and rehabilitation, anesthesiology, or radiology usually perform these injections.

The injection can work as a test. If your usual pain eases a lot while the numbing medicine is working, usually for a few hours, the SI joint is more likely to be a main source of your pain.

The test is not perfect. A single injection can point to the SI joint when it is not the main problem.

The steroid is meant to calm inflammation in and around the joint. In some people, this eases pain for weeks or longer.

An injection does not repair the joint. The hope is to ease pain enough to move more comfortably and keep up with exercise or physical therapy.

Before

Your care team will ask about blood thinners, diabetes, allergies (especially to contrast dye or numbing medicine), recent infections, and whether you could be pregnant. If you are pregnant or allergic to contrast dye, the team may use ultrasound instead of x-ray, or skip the dye.

Some blood thinners are paused before some injections, and some are not. The team will tell you what to do. Never stop a blood thinner on your own.

Many clinics ask you to bring a driver, because the numbing medicine can make a leg feel numb or weak for a few hours.

During

You usually lie face down on a padded table. The skin over the low back or upper buttock is cleaned and numbed first. Most people feel a quick sting, then pressure. Some feel a brief flash of their familiar pain as the medicine goes in.

A small amount of contrast dye is often used to confirm that the medicine is going into the joint. The injection usually takes less than half an hour, plus time for check-in and a short rest afterward.

After

You may be asked to move in ways that usually bring on your pain, and to track your pain in a diary for several hours. Relief from the numbing medicine fades within hours. If a steroid was used, any benefit may not be immediate.

Most people return to light, everyday activity the next day.

The evidence is limited, and reviews disagree about how much these injections help.

Some people get relief that lasts weeks to months. A 2025 guideline from pain specialty societies found that steroid injections in or around the joint can ease pain for at least 4 weeks in carefully selected people, though much of the evidence is low quality. [1]

Reviews by specialist groups have rated the evidence for these injections as fair to moderate. It rests on a small number of trials with mixed results. [2] [7]

A 2025 review of many trials found that injections aimed at spinal joints, including the SI joint, give little or no extra relief compared with a sham (pretend) procedure. A 2025 international guideline strongly recommends against them for long-lasting back pain. [8] [9]

The UK’s NICE guideline advises against spinal injections for low back pain. It does not name SI joint injections specifically. [11]

It is hard to predict who will get lasting relief. A good response to the numbing medicine does not always mean the steroid will help. [1] [2]

For SI joint pain that keeps coming back, some clinicians consider radiofrequency ablation, which uses heat to quiet the small nerves behind the joint. Test blocks of those nerves are often done first. Guidelines disagree about it; see radiofrequency ablation. [1] [9] [12]

Some people have an inflammatory type of arthritis that affects the SI joints. Steroid injections are sometimes part of their care, and the research and guidance for that situation are different.

Many clinicians use an injection as one part of a plan that also includes exercise and physical therapy. [1]

Common and short lived

• Soreness at the injection site for a day or two.
• A short-term increase in pain.
• If a steroid is used, higher blood sugar for a day or two in people with diabetes.

Less common

• Numbness or weakness in the leg for a few hours, if the numbing medicine spreads to nearby nerves.
• Feeling lightheaded or faint during or right after the injection.
• Flushing of the face, sweating, or feeling warm for a day or two after a steroid.

Rare but serious

• Infection in or around the joint, bleeding, or injury to a nerve.

Other downsides

• Relief is often temporary, and the pain can come back.
• Steroid doses add up. Many clinicians limit how many steroid injections someone has, partly because of effects on blood sugar and bone health.

Get emergency care right away for leg weakness or numbness that is getting worse or has not worn off when your team said it would, or new trouble controlling your bladder or bowels. Call your care team the same day for a fever, redness or drainage at the injection site, or pain that is severe and getting worse.