Sacroiliac Joint Injections
What Is the Sacroiliac Joint?
The sacroiliac joint — commonly called the SI joint — is located where your pelvis connects to the base of your spine. You actually have two of them, one on each side. These joints sit just below your lower back and above your tailbone, and if you press your thumbs into the two dimples at the very bottom of your back, you are right on top of them.
The SI joints carry a significant amount of load. Every time you walk, climb stairs, or shift your weight from one leg to the other, these joints are working. They do not move very much compared to a joint like your hip or knee — but they do need to absorb force and stay stable while allowing just enough motion to keep your pelvis balanced.
When the SI joint becomes inflamed, injured, or starts moving abnormally, it can be a significant source of pain that is often mistaken for a disc problem, hip problem, or muscle strain.
What Does SI Joint Pain Feel Like?
SI joint pain can be tricky to identify because it tends to mimic other common conditions. It is estimated that the SI joint is the primary source of pain in somewhere between 15 and 30 percent of patients with chronic low back pain — which means it is frequently missed or attributed to something else.
Common symptoms include:
Pain in the lower back, buttock, or the back of the hip — usually on one side
Pain that may travel into the groin, outer thigh, or back of the leg (though usually not below the knee)
Aching or stiffness that is worse after sitting for long periods, climbing stairs, or rolling over in bed
Pain with putting full weight on one leg, such as when getting out of a car
A feeling of instability or that your pelvis is uneven
SI joint pain is often worse with prolonged sitting or standing and may ease temporarily with movement, only to return with fatigue.
What Causes SI Joint Problems?
The SI joint can become painful for a number of reasons:
Trauma — a fall onto the buttocks, a motor vehicle accident, or a misstep off a curb can strain the joint and surrounding ligaments
Pregnancy and postpartum changes — hormones released during pregnancy loosen the ligaments around the SI joint, which can cause instability and pain that sometimes persists after delivery
Leg length discrepancy — even a small difference in leg length can alter how load is distributed through the pelvis over time
Prior lumbar fusion surgery — fusion of the lumbar spine changes how forces are transmitted through the lower back, and the SI joint often absorbs increased stress as a result
Arthritis — degenerative changes or inflammatory arthritis such as ankylosing spondylitis can affect the SI joint directly
Repetitive stress — runners, rowers, and other athletes who perform repetitive one-sided movements are at higher risk
How Is SI Joint Pain Diagnosed?
There is no single imaging finding or test that definitively diagnoses SI joint pain. X-rays and MRI can show degenerative changes or inflammation in the joint, but a normal-appearing joint on imaging does not rule out the SI joint as a pain source. Physical examination maneuvers that stress the joint — such as the FABER test, the thigh thrust, or the distraction test — can raise suspicion, but none of these alone is conclusive.
This is why a diagnostic SI joint injection plays such an important role. Just as with medial branch blocks for facet joint pain, injecting a small amount of local anesthetic directly into the SI joint is the most reliable way to confirm it as your pain source. If your pain improves significantly after the injection, the SI joint is confirmed as the target.
The SI Joint Injection: What to Expect
What is it?
An SI joint injection serves two purposes: it can be used purely as a diagnostic tool to confirm the SI joint as a pain source, or it can be therapeutic — delivering steroid medication into the joint to reduce inflammation and provide relief.
In most cases, both goals are accomplished in the same procedure. A combination of local anesthetic and corticosteroid is injected, giving your doctor diagnostic information while also treating the inflammation at the same time.
What happens during the procedure?
You will lie face down on a procedure table. The skin over the SI joint will be cleaned and numbed with local anesthetic. Your doctor will use fluoroscopy (live X-ray) or ultrasound guidance to place the needle precisely into the joint space. The SI joint has an irregular shape and a narrow opening, which is why image guidance is essential — it is very difficult to confirm accurate placement without it.
Contrast dye is injected first to confirm the needle is inside the joint before any medication is given. Once placement is confirmed, a combination of local anesthetic and steroid is injected. The procedure typically takes 15 to 30 minutes. Most patients feel pressure at the injection site and occasionally a brief, familiar reproduction of their usual pain as the needle enters the joint — this is normal and actually a useful confirmation that the needle is in the right place.
After the procedure
You will rest briefly before being discharged home. It is helpful to pay attention to your pain level over the next several hours. If the local anesthetic provides significant relief within the first few hours, that is a meaningful sign that the SI joint is the correct target.
Some soreness at the injection site is normal for one to two days. Ice applied for 15 to 20 minutes at a time can help. Avoid heat to the area for the first 48 hours. You can return to light daily activity the same day or the following day, and should avoid strenuous activity for 24 to 48 hours.
When Will I Feel Relief?
The local anesthetic may provide brief relief within the first few hours. The steroid typically takes 3 to 7 days to take full effect. Most patients who respond to the injection notice meaningful improvement within 1 to 2 weeks.
Hours 1–6: Possible early relief from local anesthetic — take note of how much your pain improves
Days 3–7: Steroid begins to take effect
Weeks 1–2: Most patients experience meaningful relief if the injection is going to work
Weeks to months: Duration of relief varies by individual
Relief from an SI joint injection can last anywhere from a few weeks to several months depending on the underlying cause and severity of the problem. The injection is most effective when paired with physical therapy that addresses movement patterns, hip strength, and pelvic stability.
What If the Injection Provides Lasting Relief?
If an SI joint injection confirms the joint as your pain source and provides good but temporary relief, there are longer-term treatment options available:
Continued injections with rehabilitation: For many patients, one to two injections combined with a focused physical therapy program addressing hip and core stability is enough to achieve lasting improvement.
SI Joint Radiofrequency Ablation: Similar to the RFA procedure used for facet joint pain, the nerves supplying the SI joint can be targeted with radiofrequency ablation to provide longer-lasting relief. This is typically considered when injections provide good but short-lived benefit and the SI joint has been clearly confirmed as the pain source.
SI Joint Fusion: For patients with severe, refractory SI joint pain that does not respond to conservative measures or injections, minimally invasive SI joint fusion is a surgical option. This is typically reserved for cases where the joint is confirmed as the sole pain generator and other treatments have failed.
Your doctor will discuss which path makes the most sense based on how you respond and what is causing your SI joint problem in the first place.
Blood Thinners and SI Joint Injections
SI joint injections are generally considered a low-to-intermediate risk procedure for bleeding. In most cases, common over-the-counter pain relievers such as ibuprofen or naproxen do not need to be stopped before the procedure.
If you are taking a prescription blood thinner — such as warfarin (Coumadin), rivaroxaban (Xarelto), apixaban (Eliquis), or clopidogrel (Plavix) — your doctor will review your specific medication before the procedure and give you individualized guidance. Do not stop any prescription blood thinner on your own without speaking to your doctor first.
Risks and Complications
SI joint injections are safe procedures, and serious complications are uncommon. Possible risks include:
Temporary soreness at the injection site — very common, resolves within a few days
Temporary pain flare — some patients notice increased SI joint pain for one to two days after the injection before improvement begins
Infection — rare, as sterile technique is used throughout
Bleeding — uncommon; discuss your medications with your doctor beforehand
Incomplete or no relief — the injection may provide less benefit than expected in some patients, which can also provide useful diagnostic information
Questions to Ask Your Doctor
How confident are you that the SI joint is the source of my pain?
Will this injection be diagnostic, therapeutic, or both?
Do I need to stop any medications before this procedure?
What physical therapy exercises should I be doing alongside this treatment?
If this injection works, what are my options for longer-term relief?
Am I a candidate for SI joint RFA if the injection provides only short-term benefit?
Are there any activity modifications I should make to protect the SI joint while it heals?
This article is for educational purposes only and does not replace a conversation with your physician. Treatment decisions should always be made together with your care team based on your individual history, exam findings, and imaging. If you have questions about whether this procedure is right for you, please schedule a consultation.