Sacroiliac joint dysfunction is a condition where one or both of the joints connecting your spine to your pelvis move abnormally, causing pain in the lower back, buttocks, or legs. It accounts for an estimated 15% to 30% of all chronic lower back pain cases, making it one of the more common and frequently overlooked sources of back pain.
What the Sacroiliac Joint Does
The sacroiliac joints (often called SI joints) are the largest joints in your spine. You have one on each side, sitting where the triangular bone at the base of your spine (the sacrum) meets the large pelvic bones. Their primary job is transferring the weight of your upper body down through your pelvis and into your legs every time you stand, walk, or lift something.
Unlike your knee or shoulder, these joints barely move. Total motion in any direction tops out at about 3 degrees of bending and 2 millimeters of sliding. That tiny range of motion acts as a shock absorber, cushioning the forces between your spine and legs. When that small, precise movement is disrupted in either direction, pain follows.
How the Joint Becomes Dysfunctional
SI joint dysfunction falls into two broad categories based on what’s gone wrong mechanically.
Too much movement (hypermobility): The ligaments holding the joint together become loose or stretched, allowing the joint to shift more than it should. This instability tends to cause pain in the lower back and hip that can spread into the groin.
Too little movement (hypomobility): The joint becomes stiff or locked in place, losing even its small normal range of motion. This typically produces pain on one side of the lower back or buttock that can radiate down the leg, sometimes mimicking sciatica.
Several things can push the joint toward either extreme. Traumatic injuries like car accidents or hard falls can damage the ligaments or jam the joint. Repetitive stress from activities with uneven loading (like always carrying a child on one hip) gradually wears the joint down. Arthritis, especially osteoarthritis, degenerates the joint surfaces over time. People with disc problems in the lower spine also have a higher rate of SI joint dysfunction: roughly one in three patients with lumbar disc herniation also has SI joint involvement.
Pregnancy and Hormonal Changes
Pregnancy is one of the most common triggers for SI joint dysfunction, particularly the hypermobility type. During pregnancy, the body produces a hormone called relaxin that remodels collagen in ligaments, making them stretchier. This loosening helps the pelvis widen for delivery, but it also reduces the stability of the SI joints. The combination of looser ligaments, shifting posture from a growing belly, and increased body weight puts significant strain on these joints. For some women, the laxity resolves after delivery. For others, the instability persists and becomes a chronic source of pain.
What SI Joint Pain Feels Like
The hallmark of SI joint dysfunction is pain centered on one side of the lower back, just beside the base of the spine. In a study of 50 patients with confirmed SI joint problems, 94% reported buttock pain and 72% reported lower lumbar pain. But the pain doesn’t always stay in one place. Half of the patients experienced pain radiating into the leg, 28% had pain below the knee, and about 14% felt it all the way into the foot. Groin pain showed up in 14% of cases.
This wide spread of possible pain locations is part of what makes SI joint dysfunction tricky. Pain radiating down the leg can look identical to a pinched nerve in the spine. Pain in the groin might be mistaken for a hip problem. One useful clue: many people with SI joint dysfunction can point to the exact spot where their pain originates, pressing one finger just below and to the side of the base of the spine. This pattern, sometimes called the Fortin Finger Sign, is a common initial indicator.
Pain often worsens with prolonged sitting or standing, climbing stairs, getting out of a car, or rolling over in bed. Activities that load one side of the pelvis more than the other tend to be the biggest triggers.
Why It’s Hard to Diagnose
Standard imaging often misses SI joint dysfunction entirely. X-rays are the usual first step, but the irregular shape and angled position of the SI joints make them difficult to assess on film. MRI can detect inflammation, but it has real limitations here. About one-third of patients with clinically confirmed SI joint problems have a completely normal MRI. Making matters worse, MRI can also overcall the diagnosis: SI joint swelling that looks like a problem on imaging shows up in nearly a third of young athletes and people with other types of back pain who don’t actually have SI joint dysfunction.
Because of these imaging gaps, diagnosis relies heavily on a physical exam. Doctors use a set of five hands-on provocative tests that stress the SI joint in different ways to see if they reproduce the patient’s pain. These include the FABER test (where the hip is flexed and rotated outward), Gaenslen’s test (which stresses both SI joints simultaneously by extending one hip while flexing the other), and compression, distraction, and thigh thrust tests. When three or more of these five tests are positive, the likelihood of SI joint involvement is high.
For cases that remain uncertain, a diagnostic injection can confirm the source. A doctor injects a local anesthetic directly into the SI joint under imaging guidance. If the injection reduces pain by at least 75%, most pain management guidelines consider that confirmation. Some recent evidence suggests that patients with even 50% relief from a diagnostic block still benefit from treatment, which has expanded the criteria in some clinical settings.
Conservative Treatment Options
Most people with SI joint dysfunction start with non-surgical treatment, and many improve significantly with it. Over-the-counter anti-inflammatory medications like ibuprofen or naproxen help reduce the swelling that contributes to pain. Acetaminophen can manage discomfort as well, though it doesn’t address inflammation directly.
Physical therapy is the cornerstone of long-term management. For hypermobility, the focus is on stabilization: strengthening the muscles that support and compress the SI joint. Key targets include the gluteus maximus, the deep core muscles, and the pelvic floor muscles, all of which attach to or influence the SI joint through their connections to surrounding tissue. For hypomobility, therapy focuses more on manual techniques to restore the joint’s small range of motion, combined with stretching of the surrounding muscles.
An SI joint belt, a snug band worn around the pelvis, can provide external compression that compensates for loose ligaments. This is especially helpful during pregnancy or postpartum recovery when hormonal laxity is the primary driver. Ice and heat, applied to the affected side, offer simple short-term relief between therapy sessions.
Injections and Procedures
When conservative measures aren’t enough, corticosteroid injections into the SI joint can reduce inflammation and provide relief lasting weeks to months. These are performed under fluoroscopy or ultrasound guidance to ensure accurate placement. Some patients get lasting benefit from a single injection; others need periodic repeat injections.
Radiofrequency ablation is another option. This procedure uses heat to disrupt the nerves that carry pain signals from the SI joint, providing longer-lasting relief than steroid injections alone. The nerves eventually regenerate, so the effect is temporary, but it can last six months to a year or more.
When Surgery Is Considered
Minimally invasive SI joint fusion is reserved for patients who haven’t responded to at least six months of conservative care and injections. The procedure involves placing small implants across the joint to lock it in place, eliminating the abnormal motion that causes pain. It’s a short procedure, averaging about 73 minutes, with minimal blood loss and an average hospital stay under one day.
Outcomes are favorable for well-selected patients. In a multicenter study tracking patients for a year after surgery, nearly 92% achieved substantial pain reduction, and about 96% said they would have the surgery again. Recovery involves a period of partial weight-bearing with a walker, followed by a gradual return to full activity over several weeks.