Sacroiliac Joint Dysfunction: Why SI Joint Pain Is Often Missed
Sacroiliac joint dysfunction means pain is coming from one or both SI joints—the sacroiliac joints that connect the spine to the pelvis. It is often missed because a lumbar MRI, the scan of the lower back, is built to show discs, nerves, bones, and the spinal canal—not to prove whether the SI joint is the pain generator.
In my practice, I think about the SI joint when a patient has real buttock or low back pain but the lumbar MRI shows no clear nerve compression. What matters isn’t whether the MRI looks normal—it’s whether the symptoms, exam, and imaging all point to the same pain source.
What SI joint dysfunction means
The sacroiliac joints connect the sacrum—the triangle-shaped bone at the base of your spine—to the pelvis, the ring of bones that supports your hips and legs. You have one on each side. Each is small compared with the hip or knee but sits where the spine transfers weight into the pelvis and legs. These joints normally move only a little, yet they can still become painful.
“Dysfunction” is a broad term. It may mean:
- Joint irritation or pain from the joint surface.
- Inflammation (swelling or irritation in tissue).
- Abnormal motion.
- Degeneration (wear-and-tear change over time).
- Pain from nearby ligaments, the strong bands of tissue connecting bones.
SI joint dysfunction is a pain diagnosis, not just an MRI finding. It is diagnosed from the pain location, exam, imaging context, and sometimes response to an injection—not from a scan alone.
Where SI joint pain is usually felt
SI joint pain often shows up in one or more of these areas:
- One side of the low back.
- The “dimple” area just off the midline.
- The buttock.
- The outer hip.
- The groin.
- The upper thigh.
Some people feel pain that seems like sciatica—pain traveling down the leg from an irritated or compressed spinal nerve. SI joint pain can mimic it but often does not follow a classic nerve pattern. For true nerve-related leg pain, see Sciatica: Causes, Diagnosis, and the Treatment Path.
Buttock, hip, and upper leg pain can come from many places. Besides lumbar disc herniation and spinal stenosis—both covered below—SI joint pain overlaps with hip arthritis or labral problems (the labrum is the ring of cartilage around the hip socket), piriformis or deep gluteal pain (a small muscle deep in the buttock), facet joint pain from the small joints at the back of the spine, and simple muscle strain. Symptoms alone are not enough to prove the SI joint is the cause.
Why the SI joint is so often missed
Patients and doctors tend to focus on the lumbar MRI report—but that report may describe several age-related spine findings while saying little about the SI joints. A standard lumbar MRI is built to look at the discs, nerves, vertebrae (the bones of the spine), spinal canal, and the areas where nerves exit. It is not always designed to evaluate the SI joints.
SI joint pain also tends not to create a dramatic MRI finding—you can have significant pain without a scan showing a clear “smoking gun.” Meanwhile, lumbar reports often show mild disc bulges or degenerative changes that are common with age and appear even in people without back pain. They can be real, but they may not be the main pain source.
That does not mean MRI findings should be ignored; it means they must be matched to the story. In my practice, what I look for is not just whether there are disc bulges, but whether the imaging actually matches the patient’s pain pattern. For more on age-related findings, see Degenerative Disc Disease: What “Normal Aging” Looks Like on Your MRI.
What causes it
SI joint pain can have more than one cause—it is not always a simple “misalignment.” Possible contributors include:
- Prior trauma or a fall.
- Pregnancy or postpartum (after-childbirth) changes, including ligament looseness and shifting pelvic load.
- Prior lumbar fusion, surgery that joins two or more spine bones together.
- Degenerative joint changes.
- Inflammatory arthritis such as ankylosing spondylitis, which can inflame the spine and SI joints, and other spondyloarthropathies affecting the spine and pelvis.
- Leg length difference or altered gait (the way you walk).
- Repetitive mechanical stress.
- Sometimes no single clear cause.
After lumbar fusion, some patients develop or continue pain that may come from the SI joint, because more stress can be transferred to the pelvis. But not all pain after spine surgery is SI-related—other causes still need to be considered.
How doctors diagnose SI joint pain
The diagnosis comes from putting several pieces together; no single symptom, test, or scan proves it alone.
History and pain location
Doctors ask where the pain is, whether it stays on one side, what movements worsen it, whether it travels below the knee, and whether numbness, tingling, or weakness is present—features that help separate nerve compression, hip disease, and SI joint pain. Common SI-region triggers include stairs, standing on one leg, getting in and out of a car, rolling in bed, prolonged standing, and moving from sitting to standing. These raise suspicion but do not diagnose the condition by themselves.
Physical exam maneuvers
Doctors use hands-on provocative tests that stress the SI joint to reproduce your familiar pain:
- FABER/Patrick test: the hip is placed in a figure-four position to stress the hip and SI area.
- Thigh thrust: pressure is applied through the thigh to load the SI joint.
- Compression test: the pelvis is gently compressed from the side.
- Distraction test: the front of the pelvis is gently stressed apart.
- Gaenslen test: the hips are positioned to stress one side of the pelvis.
- Sacral thrust: pressure is applied over the sacrum.
No single test is perfect. A cluster of positive tests means more than any one, especially when pain location, exam, and injection response agree.
Imaging
A lumbar MRI can help show or rule out competing causes—disc herniation, spinal stenosis, nerve compression, fracture, and, in certain settings, tumor or infection. Doctors may also order pelvic or dedicated SI joint X-rays, a CT scan (a detailed bone scan), a dedicated SI joint MRI, or a pelvic MRI. SI joint imaging may show arthritis, inflammation, sclerosis (hardening or thickening of bone near a joint), erosions (small areas of bone loss from inflammation), or partial-to-complete fusion of the joint. Still, imaging alone does not always prove the SI joint is the pain source.
Diagnostic injection
A diagnostic injection helps identify where pain is coming from. For a suspected SI joint, doctors use an image-guided injection (X-ray or CT positions the needle) that often includes a local anesthetic, or numbing medicine. If numbing the joint temporarily relieves your typical pain, that supports the SI joint as the pain generator—though it is not a perfect test. Doctors weigh how much relief occurred, how fast it started and how long it lasted, whether it fit the anesthetic’s expected action, and whether the treated pain was the pain you usually feel, all read in full clinical context.
Telling it apart: disc herniation, sciatica, stenosis, and hip pain
In my practice I am cautious about blaming the SI joint too quickly, because hip disease, lumbar stenosis, and disc herniations all create overlapping symptoms.
vs lumbar disc herniation
A disc herniation—where the soft inner part of a spinal disc pushes through the tougher outer layer—often causes nerve-root symptoms (a nerve root is a nerve branch exiting the spine): pain, numbness, tingling, or weakness down the leg in a fairly specific pattern. SI joint pain more often stays in the low back, buttock, hip, groin, or upper thigh, though overlap happens. See Lumbar Disc Herniation: A Surgeon’s Patient Guide.
vs sciatica
True sciatica means an irritated or compressed lumbar nerve root. SI joint pain can radiate into the buttock or upper leg and mimic it, but often without any nerve compression. More detail: Sciatica: Causes, Diagnosis, and the Treatment Path.
vs lumbar spinal stenosis
Stenosis—narrowing around the spinal nerves in the lower back—often causes leg symptoms with standing or walking, and many people feel better sitting or bending forward. SI joint pain is usually more localized and tends to worsen with transitions, stairs, or loading one side of the pelvis. See Lumbar Spinal Stenosis: A Plain-Language Guide for Patients.
vs hip disease
Hip joint pain often shows up in the groin and worsens when the hip is rotated. SI joint pain is usually more posterior (toward the back), felt near the buttock or low back dimple. The overlap can be substantial, and some people need both the hip and the spine/SI region evaluated.
Treatment options
Treatment depends on how strong the diagnosis is, how severe the symptoms are, and what else is going on. Before procedures like ablation or fusion, I want a consistent story pointing to the SI joint as the main pain generator.
Conservative care
Most people start with non-surgical care: activity changes, physical therapy, anti-inflammatory medicines when safe and appropriate, heat or ice, and short-term symptom control. Physical therapy may focus on pelvic stability, hip strength, core control (the muscles around the abdomen, back, and pelvis), gait mechanics, and safe movement during stairs, transfers, and lifting. It should be individualized—a movement that helps one person may flare another.
SI joint injections
An SI joint injection may be used for diagnosis, treatment, or both. A steroid injection uses anti-inflammatory medicine to calm irritated tissue and may reduce pain, though relief varies widely—short-term for some, longer for others, little for a few. A future SpineClarity guide will compare SI joint injection vs radiofrequency ablation.
Radiofrequency ablation
Radiofrequency ablation (RFA) uses heat energy to target the small sensory nerves—the nerves that carry pain signals—around the SI joint. It does not repair, rebuild, or realign the joint; it is meant to reduce pain signaling, and may be considered in selected patients when diagnostic blocks suggest SI-mediated pain.
SI joint fusion
SI joint fusion is surgery that joins the joint so it moves less. It is generally reserved for carefully selected patients with persistent, function-limiting SI joint pain that has not improved with non-surgical care, exam findings that fit, imaging that shows no better explanation, and diagnostic evidence pointing to the SI joint. It is not the first step for most people. A future guide will explain when SI joint fusion is considered.
When your MRI doesn’t explain your pain
A person can have SI joint pain and lumbar spine changes at once, and MRI findings—disc bulges, facet arthritis, stenosis, degenerative disc disease—may or may not be the main generator. Other spine conditions can overlap with SI-region pain too:
- Spondylolisthesis, where one spine bone has slipped forward on the one below it.
- Adult degenerative scoliosis, a wear-and-tear spinal curve in adults.
- Vertebrogenic pain, from irritated bone and nerve endings near the spinal endplates (the top and bottom surfaces of a spinal bone next to the disc).
So if you have been told your MRI is “mild” or “normal”—“mild degenerative changes,” “no significant stenosis,” “small disc bulge,” “no clear nerve compression”—that does not mean your pain isn’t real. It means the scan may not show the whole story, and the source could be in the spine, hip, SI joint, muscles, tendons, or a combination. The next step is to put the report, symptoms, and prior treatments into one clear clinical picture.
SpineClarity offers a written MRI/case review from a board-certified spine surgeon. You can upload your symptoms, MRI report, and relevant records and receive a plain-language written interpretation with a suggested next-step category. This is not emergency care and does not replace an in-person physician relationship, but it can help you understand whether your imaging findings seem to match your symptoms—or whether another source, such as the SI joint, needs to be considered.
Red flags: when to seek urgent care
SI joint dysfunction is usually not an emergency by itself, but certain symptoms are not typical SI joint pain and need urgent evaluation. Seek urgent or emergency care if you have:
- New or worsening leg weakness.
- Loss of bowel or bladder control.
- Numbness in the groin, inner thighs, or saddle area.
- Fever, chills, or concern for infection.
- History of cancer with new severe spine or pelvic pain.
- Major trauma or a fall.
- Unexplained weight loss with worsening pain.
- Severe, rapidly worsening pain.
- Inability to walk or stand safely.
Loss of bowel or bladder control, saddle numbness, or severe new neurologic symptoms can signal cauda equina syndrome—a spine emergency in which the bundle of nerves at the bottom of the spinal canal is compressed. Learn more: Cauda Equina Syndrome: The Spine Emergency Patients Need to Recognize.
Common questions
Can SI joint dysfunction show up on MRI?
Sometimes. Dedicated SI joint imaging may show inflammation, arthritis, sclerosis, erosions, or joint fusion. But many cases of SI-mediated pain are not obvious on a standard lumbar MRI, which is built to look at the lower spine, discs, nerves, and spinal canal—so it may not confirm or exclude SI joint pain.
Is sacroiliac joint dysfunction serious?
It is usually not dangerous, but it can be very painful and can limit walking, sitting, sleep, work, and daily life. It is not an emergency unless red flags are present—new weakness, loss of bowel or bladder control, saddle numbness, fever, cancer history with new severe pain, major trauma, or inability to walk.
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