Sacroiliac Joint Injections: Everything Patients Want to Know

The sacroiliac joint — the joint where the base of the spine meets the pelvis — is one of the most overlooked sources of chronic lower back pain. Many patients spend months or years treating back pain that actually originates in the SI joint, often without realizing the SI joint exists. Once correctly identified, SI joint pain often responds well to targeted treatment. This guide walks through what the SI joint is, how SI joint pain is recognized, and what a sacroiliac joint injection involves.

What the Sacroiliac Joint Is

You have two sacroiliac (SI) joints, one on each side. Each SI joint sits where the sacrum — the triangular bone at the base of your spine — meets the iliac bones of your pelvis. The joint is held together by strong ligaments, and it has limited movement compared to other joints. Its main function is to transfer forces between the spine and the legs, which is why it is involved in walking, standing, sitting, and essentially every activity that puts load on the lower body.

Because the SI joint moves less than, say, the hip or knee, it is often assumed to be a “non-issue.” But the joint can develop several problems — inflammation, instability, arthritis, ligament strain — any of which can produce persistent pain.

When the SI Joint Is the Source of Pain

SI joint pain is often misdiagnosed as lumbar pain or hip pain because it can feel like either one. Characteristic features that point toward the SI joint:

• Pain felt predominantly on one side, at the lower back, just above the buttock
• Pain that can radiate into the buttock, groin, or upper thigh — rarely past the knee
• Worsens with specific positions: rising from a seated position, standing for long periods, stairs, walking uphill
• Often worsens with prolonged sitting with one leg crossed over the other
• May worsen with unequal weight-bearing (standing on one leg, stepping on a curb)
• Pain with direct pressure over the back of the SI joint

Physical examination maneuvers specifically designed to stress the SI joint help identify it as the source. Imaging is less helpful for SI joint pain than for many other back pain problems — the joint may look normal on MRI even when it is clearly the pain source clinically. This is why a careful physical examination matters so much.

What Causes SI Joint Pain

Several situations commonly produce SI joint pain:

Post-pregnancy or postpartum. Ligament changes during pregnancy can lead to SI joint laxity and pain that sometimes persists afterward.

Trauma. A fall onto one side of the lower body, a motor vehicle accident, or any event that loads the SI joint asymmetrically can strain it.

Arthritis. Age-related arthritic changes in the joint.

Post-lumbar-fusion. Patients who have had lumbar spine fusion surgery sometimes develop SI joint pain because the altered biomechanics put more load on the joint.

Ankylosing spondylitis and related conditions. Inflammatory conditions that can affect the SI joints.

Leg length discrepancy. Significant differences in leg length can chronically overload one SI joint.

Unclear onset. Many patients develop SI joint pain without a clearly identifiable triggering event.

The Role of Diagnostic Injections

Because SI joint pain is often not clearly identifiable on imaging and because several other sources of lower back pain can mimic it, a diagnostic SI joint injection is often used to confirm (or rule out) the SI joint as the pain source.

In a diagnostic injection, a local anesthetic is placed precisely into the SI joint under image guidance. If the patient’s typical pain is significantly relieved for the duration that the anesthetic would be expected to last (typically hours), that is strong evidence the SI joint is the source. If the pain is not affected, the SI joint is probably not the source, and attention shifts to other structures.

A therapeutic SI joint injection typically combines an anesthetic with a corticosteroid, aiming not just to diagnose but to reduce inflammation and provide longer-lasting relief.

How the Procedure Is Performed

A typical SI joint injection involves:

Preparation. You change into a gown and are positioned face-down on an imaging table. The lower back and gluteal area are cleaned and draped.

Local anesthetic. A small amount of local anesthetic numbs the skin and deeper tissues.

Image guidance. The procedure is performed under fluoroscopy. SI joint anatomy is difficult to target precisely without imaging — the joint is an oblique space that is nearly impossible to reliably enter blindly. Image guidance is standard.

Needle placement. Your physician advances the needle into the SI joint. Contrast dye is typically used to confirm placement inside the joint.

Medication injection. The anesthetic alone (for a diagnostic block) or anesthetic plus corticosteroid (for a therapeutic injection) is slowly injected.

Monitoring and discharge. Brief observation, post-procedure instructions, and release. You are often asked to keep a pain diary for the first few hours to help determine whether the anesthetic portion of the injection produced meaningful relief — this is key diagnostic information.

The procedure itself typically takes 15 to 25 minutes.

What to Expect From the Procedure

During. The injection involves some pressure sensation. Most patients tolerate it well.

Immediately after. The anesthetic effect provides a window of relief that is diagnostically important. If your pain during this window is significantly better than baseline, that suggests the SI joint is the source. As the anesthetic wears off (within a few hours), pain may return briefly before the steroid effect begins.

Over the following days. The steroid effect typically begins within a few days. Meaningful relief, when it occurs, usually develops over the following week.

Over the following weeks to months. When the injection works, benefit typically continues. Duration varies considerably — some patients get weeks of relief, others get months. Some do not respond and move on to a different approach.

What Comes After

For patients whose SI joint injection confirms the joint as the pain source and provides meaningful relief:

Repeat injections. Sometimes appropriate, with guidelines on spacing and total number per year.

Radiofrequency procedures. For patients whose pain responds well to diagnostic blocks but whose relief from therapeutic injection is shorter than desired, a radiofrequency procedure targeting the nerves that carry pain signals from the SI joint can provide longer-lasting relief in selected cases.

SI joint fusion. For a small subset of patients with well-documented SI joint pain who have failed comprehensive non-surgical management, a minimally invasive SI joint fusion procedure is sometimes considered. This is a surgical procedure performed by specialists who do it and is not appropriate for most SI joint patients.

Continued non-surgical management. Most SI joint patients do well with periodic injections combined with physical therapy, appropriate exercise, and sometimes a pelvic brace for specific situations.

Physical Therapy and Exercise

Most SI joint patients benefit from a specific kind of physical therapy focused on core and pelvic stabilization. Strengthening the muscles that support the SI joint — glutes, core, hip stabilizers — reduces the load on the joint and often helps both acute symptoms and long-term resilience.

An injection that reduces pain often makes physical therapy substantially more productive. This combination typically produces better long-term results than either alone.

SI Joint Injections at Southwest Pain Management

Our clinics perform diagnostic and therapeutic SI joint injections for appropriate patients, always with image guidance. The SI joint is a common enough pain generator that evaluating for it is part of any thorough lower back pain workup. Our team is led by Philip Morgan, MD.

Frequently Asked Questions

How do I know if my pain is from the SI joint versus my lower back? Pattern of pain and physical examination offer strong clues. Definitively, a diagnostic injection is often used to confirm the SI joint as the source.

Is an SI joint injection safe? Considered generally safe when performed by a trained specialist with image guidance. As with any procedure, it carries some risks, which your physician will review.

How long does relief last? Varies from weeks to months. Multiple injections are sometimes appropriate.

Can the SI joint pain come back? Often yes, because the injection does not fix the underlying mechanical issue. This is why most SI joint plans also include physical therapy and, when relevant, activity modification.

Will I need SI joint fusion surgery? Most SI joint patients are managed successfully without surgery. Fusion is considered in a small subset of patients with well-documented SI joint pain who have failed comprehensive non-surgical management.

Do I need an MRI before an SI joint injection? Not always. MRI often looks normal even in clear SI joint pain. Your physician will discuss whether imaging is needed in your case.

What activities should I avoid with SI joint pain? Your physician will give specific guidance. In general, activities that asymmetrically load the pelvis — prolonged sitting with crossed legs, stepping onto something with one leg, carrying heavy loads on one side — are often worth modifying while you work through treatment.

Request a Consultation

Contact Southwest Pain Management to discuss whether an SI joint evaluation is the right next step.