SIJ pain is pain originating from the sacroiliac joint, a large joint where your lower spine meets your pelvis on each side. It accounts for roughly 10% to 25% of all chronic lower back pain cases, making it one of the most common and most overlooked sources of persistent pain below the waistline. Because it mimics other back problems, many people go months or years before getting the right diagnosis.
Where the Sacroiliac Joint Sits and What It Does
You have two sacroiliac joints, one on each side of your lower spine. Each joint connects the triangular bone at the base of your spine (the sacrum) to the large wing-shaped bones of your pelvis (the ilia). If you put your hands on your hips and slide your thumbs toward your spine, the two dimples you feel are roughly where the joints sit.
The sacroiliac joints don’t move much. They shift only a few millimeters during normal activity. Their primary job is transferring the weight of your entire upper body down through your pelvis and into your legs. Every force generated by back muscles acting on the spine or pelvis passes through these joints, which means they absorb enormous loads during everyday movements like walking, bending, and lifting. Strong ligaments and surrounding muscles keep them locked in place, but when something disrupts that stability, pain follows.
What SIJ Pain Feels Like
The hallmark of sacroiliac joint pain is a deep, one-sided ache in the lower buttock, right next to the base of the spine. Most people can point to the exact spot with one finger, just below and toward the middle of the bony bump you feel at the back of your pelvis. Clinicians actually use this as a screening tool: if you can consistently pinpoint the same small area with a single finger, sacroiliac dysfunction moves higher on the list of suspects.
From that focal point, the pain often radiates. Common patterns include spreading into the upper thigh, the groin, or across the buttock. Some people feel it wrapping around the hip. It rarely travels below the knee, which helps distinguish it from sciatica caused by a pinched nerve in the spine. Sitting for long periods, standing on one leg, climbing stairs, and rolling over in bed tend to make it worse. Many people notice it flares when transitioning between positions, like standing up from a chair.
Common Causes and Risk Factors
SIJ pain generally falls into two categories: too much movement in the joint or too little. Hypermobility, where the joint moves more than it should, often results from ligament loosening. Pregnancy is a classic trigger. Rising levels of estrogen and the hormone relaxin loosen pelvic ligaments to prepare for delivery, and the growing weight of the baby adds mechanical stress. This combination can destabilize the sacroiliac joints, which is why so many pregnant and postpartum women develop pain in exactly this area.
On the other end, hypomobility (a stiff, restricted joint) can develop from arthritis, prior pelvic surgery, or age-related degeneration. Other common contributing factors include leg length discrepancy, which shifts weight unevenly through the pelvis with every step, and repetitive asymmetric loading from activities like running on a cambered road or always carrying a child on the same hip. Inflammatory conditions like ankylosing spondylitis target the sacroiliac joints early in the disease process, so persistent SIJ pain in a younger adult, especially with morning stiffness lasting more than 30 minutes, warrants closer investigation.
Falls that land directly on the buttock, car accidents, and any trauma that jolts the pelvis can also damage the joint or its ligaments. Previous lumbar spine fusion surgery is another recognized risk factor, because fusing the lower vertebrae forces the sacroiliac joints to absorb more stress than they were designed for.
How SIJ Pain Is Diagnosed
Diagnosing sacroiliac joint pain is tricky because imaging often looks normal. X-rays and MRIs frequently show no abnormality even when the joint is clearly the pain source. Unlike a herniated disc or a fracture, sacroiliac dysfunction is a functional problem, meaning the joint isn’t working properly, but the structural damage may be too subtle to see on a scan.
Instead of relying on imaging, clinicians use a battery of five hands-on provocation tests. Each one stresses the sacroiliac joint in a different direction. Individually, these tests are unreliable. But when three or more of the five reproduce your familiar pain, the diagnosis becomes much more confident, with sensitivity around 94% and specificity around 78%. This clinical decision rule is the standard approach recommended by the American Academy of Family Physicians.
For cases that remain uncertain, a diagnostic injection serves as the closest thing to a gold standard. A doctor injects a local anesthetic directly into the joint under image guidance. If you get at least 70% pain relief while the numbing agent is active, it confirms the sacroiliac joint as the source. This is often done twice with different anesthetics to rule out placebo response.
Physical Therapy and Exercise
Conservative treatment is the first line for SIJ pain, and for many people it resolves the problem entirely. The core strategy is stabilizing the pelvis by strengthening the muscles that support the joint. Physical therapy programs focus heavily on deep abdominal muscles and the glutes. Exercises like bridging (lying on your back with knees bent and lifting your hips while squeezing your glutes) and bird dogs (extending opposite arm and leg from a hands-and-knees position) train the muscles that control pelvic alignment.
The key cue across most sacroiliac exercises is drawing your belly button toward your spine before initiating the movement. This activates the deep stabilizers that act like a natural brace around the joint. Stretching tight hip flexors and hamstrings also helps by reducing the asymmetric pull on the pelvis. A physical therapist can identify which specific imbalances are driving your pain and tailor a program accordingly.
Pelvic Belts: Limited Evidence
Sacroiliac belts wrap around the hips to compress the pelvis and theoretically stabilize the joint. They’re inexpensive and widely recommended, but the research is underwhelming. In a controlled study, a pelvic belt applied at moderate tension produced an average pain reduction of only 0.5 points on a 10-point scale, which falls below the threshold for a clinically meaningful effect. About half of patients with SIJ pain experienced some short-term benefit, but only to a limited degree. Wearing the belt at maximum tightness actually increased pain slightly in some patients. If a belt feels helpful during specific activities, there’s no harm in using one, but it shouldn’t be the cornerstone of your treatment plan.
Injections and Radiofrequency Ablation
When physical therapy and lifestyle modifications aren’t enough, the next step is typically a steroid injection into the joint. This delivers anti-inflammatory medication directly to the pain source and can provide meaningful relief, but the effect is usually short to intermediate term, often fading within weeks to a few months.
For longer-lasting results, radiofrequency ablation uses heat to disrupt the nerves that carry pain signals from the joint. In a multicenter comparative study, about 52% of patients who received cooled radiofrequency ablation achieved at least 30% pain reduction, and roughly 42% experienced a 50% or greater drop in pain, compared to just 4% to 7% improvement in those receiving standard medical management alone. The pain relief from ablation typically lasts several months to over a year, though nerves can regenerate over time, and the procedure may need to be repeated.
When Surgery Becomes an Option
Sacroiliac joint fusion is reserved for people whose pain has not responded to conservative treatments or injections. The procedure uses small implants placed across the joint to eliminate the movement causing pain. It’s now done through minimally invasive techniques with relatively small incisions.
Outcomes are generally favorable. More than 4 out of 5 people who undergo the procedure report noticeable, lasting pain relief. Most patients say the surgery reduces their pain by at least half, and that improvement holds even years later. Recovery involves several weeks of limited weight-bearing, followed by a gradual return to normal activity. It’s not a first resort, but for people who have clearly confirmed SIJ pain and have exhausted other options, fusion has a strong track record.