Sacroiliac Joint Injection FAQ

What is the sacroiliac joint?

The sacroiliac (SI) joints are where the triangular bone at the base of the spine (the sacrum, in the "small of the back" below the belt) meets the ilium, one of the pelvic bones. In other words, they're where the lowest part of your spine connects to your pelvis.

What kind of pain can an SI problem cause?

Inflammation of the joint — sacroiliitis — causes pain in the low back and buttocks, and more rarely in the abdomen, groin, or leg. It can also irritate the nearby piriformis muscle in the buttock (roughly where your back pants pocket sits), adding to the picture.

What causes sacroiliitis?

At least 2–3% of people may have it. It occurs most often in younger people who carry a specific gene (HLA-B27) and/or have an inflammatory arthritis such as ankylosing spondylitis, psoriatic arthritis, or reactive arthritis (Reiter's). Recent infections can precede it — genitourinary infections in men, or gynecological/urinary infections in women. Because it can be the first sign of an inflammatory arthritis, a new diagnosis sometimes warrants a rheumatology workup.

How is the diagnosis made?

It's genuinely difficult — no single test proves it. The diagnosis is assembled from the pattern and timing of pain, what activities bring it on, family history, blood tests for inflammation, and physical exam findings (tenderness over the joint, pain with pelvic compression maneuvers, and a positive Patrick's test — pain on the opposite side when the leg is crossed). Bone scans and MRI can show joint disease. Other causes must be ruled out along the way.

How is it treated?

Anti-inflammatory medications and exercise come first. When those aren't enough, injecting a powerful anti-inflammatory (corticosteroid) directly into the joint can help a great deal — and because local anesthetic is injected at the same time, it also helps confirm the diagnosis: if numbing the joint relieves your pain, that's a good indicator the joint is the source.

What happens during the procedure?

You'll lie on your stomach. The skin is scrubbed sterile and a small area numbed (it stings briefly). A very small needle is guided into the joint — sometimes with X-ray guidance to confirm placement — and a mixture of anesthetic and steroid is injected. One or both joints may be treated, depending on where your usual pain is.

What happens afterward?

You'll get up, walk, and try to reproduce your usual pain so you can report the percentage of relief, then track it over the next few weeks in a "pain diary." The leg may occasionally feel weak or numb for a few hours. As the anesthetic wears off you'll typically be sore at the injection site for a few days, and the steroid's anti-inflammatory relief usually begins 2–3 days later.

How should I prepare?

A light meal within a few hours beforehand is fine. Insulin-dependent diabetics should not change their normal eating pattern. Take your routine medications (blood pressure, diabetes), but call ahead if you're on Coumadin (a blood thinner) or are diabetic so we can advise on timing. Arrive about 20 minutes early and expect to be at the facility roughly an hour. A driver must accompany you and get you home — no driving the day of the procedure. Most patients return to normal activities, including work, the next day.