What Is the Sacroiliac (SI) Joint?

The sacroiliac (SI) joints are the two joints that connect the base of the spine (the sacrum) to the pelvis (the iliac bones). You have one on each side.

Although they allow only small movements, these joints play a major role in:

• Transferring weight from the upper body to the legs

• Stabilizing the pelvis during walking

• Absorbing shock

When the SI joint becomes inflamed or dysfunctional, it can cause significant lower back and buttock pain, sometimes mimicking a lumbar disc problem.

What Is an SI Joint Injection?

A sacroiliac joint injection is a minimally invasive procedure that delivers anti-inflammatory medication directly into the SI joint under imaging guidance.

It serves two important purposes:

Diagnostic:
To confirm that the SI joint is truly the source of pain.

Therapeutic:
To reduce inflammation and provide symptom relief.

Because the SI joint sits deep within the pelvis, accurate placement requires fluoroscopic (x-ray) guidance.

Symptoms of SI Joint Dysfunction:

SI joint pain often presents as:

• Pain in the lower back, usually below the belt line

• Buttock pain

• Pain that may radiate into the groin or upper thigh

• Pain worsened by prolonged standing

• Pain during transitions (sitting to standing)

• Discomfort when climbing stairs

Unlike classic nerve root compression, SI pain typically does not cause true numbness or weakness in the leg.

Who Is a Good Candidate?

You may be a candidate for an SI joint injection if:

• Physical exam maneuvers reproduce SI joint pain

• Imaging supports possible SI inflammation

• Pain has not improved with conservative care

• You have persistent pain following lumbar fusion surgery

• Your symptoms are mechanical and localized to the pelvis

A careful clinical evaluation is essential because SI pain can overlap with lumbar spine conditions.

How the Procedure Is Performed?

1. You lie comfortably on your stomach.

2. The skin is cleaned and numbed with local anesthetic.

3. Using fluoroscopic guidance, a needle is precisely placed into the SI joint.

4. Contrast dye confirms correct placement.

5. A mixture of anesthetic and corticosteroid is injected.

The procedure typically takes 10–20 minutes and is performed on an outpatient basis.

What Should I Expect After the Injection?

Immediately after the injection, you may feel:

• Temporary numbness

• Immediate pain relief (from local anesthetic)

• Mild soreness at the injection site

If the SI joint is the true pain generator, the anesthetic portion may produce significant short-term relief. The steroid portion may begin working within several days.

How Long Does Relief Last?

Relief duration varies:

• Diagnostic relief may last several hours

• Therapeutic steroid relief may last weeks to months

• Some patients require repeat injections based on response

If injections provide temporary but meaningful relief, additional treatment options such as SI joint radiofrequency ablation may be considered.

Benefits of SI Joint Injection:

• Minimally invasive

• Outpatient procedure

• Helps confirm diagnosis

• Reduces inflammation

• Improves participation in physical therapy

• May delay or avoid surgical intervention

Risks and Side Effects:

SI joint injections are generally safe, but potential risks include:

• Temporary increase in pain

• Bleeding

• Infection (rare)

• Allergic reaction

• Transient leg weakness from anesthetic

Your physician will review medications and risk factors before the procedure.

Frequently Asked Questions:

Is SI joint pain the same as sciatica?
No. Sciatica typically involves nerve root compression. SI joint pain originates from the joint connecting the spine to the pelvis.

Will I be asleep?
The procedure is typically performed with local anesthetic. Sedation may be used depending on individual circumstances.

What if the injection doesn’t help?
If there is no meaningful relief, the SI joint may not be the primary pain source, and further evaluation may be needed.

Reference:

Cedar Sinai Website: “Sacroiliac Joint Dysfunction.”