Sacroiliac Joint Dysfunction (SI Joint Pain)

What the SI joints do

The two sacroiliac joints sit on either side of the sacrum, the triangular bone at the base of the spine, where it meets the iliac bones of the pelvis. You can find them under the two dimples above the buttocks. They are strong, ridged joints held by some of the toughest ligaments in the body, and they move only a few degrees. Their job is to transfer weight between the spine and the legs and to absorb shock when walking.

Pain can arise when the joint moves too much (hypermobility), too little (hypomobility), or becomes inflamed (sacroiliitis). Dysfunction is a broad term that covers these mechanical problems.

Symptoms of SI joint pain

• aching or sharp low back pain and buttock pain, usually on one side, below the level of L5 (the belt line)
• pain that may spread into the groin, hip or back of the thigh, and sometimes to the lower leg, but rarely below the knee in the pattern of a pinched nerve
• pain when standing up from sitting, climbing stairs, getting out of a car, rolling in bed or standing on one leg
• pain when sitting on the affected side
• a feeling of the pelvis or leg "giving way"
• stiffness, especially after sitting

Fortin finger sign: people with SI joint pain often point with one finger to a spot just below and inside the bony bump at the back of the pelvis (the posterior superior iliac spine).

Causes and risk factors

• Pregnancy: the hormone relaxin loosens pelvic ligaments, and weight gain and posture changes add load. SI pain is part of pelvic girdle pain, which affects many pregnant people.
• Trauma: falling onto the buttocks, car crashes or sudden twisting while lifting.
• Arthritis: wear-and-tear osteoarthritis, and inflammatory spondyloarthritis such as ankylosing spondylitis, which characteristically starts in the SI joints.
• Previous lumbar fusion: fusing lower back levels shifts stress to the SI joints.
• Uneven loading: leg length difference, scoliosis, a limp, or long-distance running.
• Infection: rare, but possible after pregnancy, in people who inject drugs or with weakened immunity.

SI joint pain vs other causes of low back pain

These overlap, and some people have more than one source of pain, for example a herniated disk together with SI joint strain.

How it is diagnosed

No single test is reliable. Doctors combine:

• History and examination of the back, hips and pelvis
• Provocation tests: the distraction, compression, thigh thrust, Gaenslen and FABER tests stress the SI joint in different ways. Three or more positive tests out of five make SI pain much more likely.
• Imaging: X-rays and MRI do not show mechanical dysfunction well but are used to look for sacroiliitis, fractures, infection or other causes. MRI can show early inflammatory changes of spondyloarthritis.
• Blood tests such as CRP and HLA-B27 if inflammatory arthritis is suspected
• Diagnostic SI joint injection: a local anesthetic is injected into the joint under X-ray or CT guidance. Major short-term pain relief supports the SI joint as the pain source.

Treatment

Self-care and physical therapy

• Stay active within comfortable limits. Prolonged bed rest slows recovery.
• Ice or heat for 15 to 20 minutes at a time.
• Physical therapy: exercises to strengthen the deep abdominal, gluteal and pelvic floor muscles, improve hip mobility and correct movement patterns. Manual therapy may give short-term relief.
• SI joint (pelvic) belt: worn snugly around the hips below the waist to stabilize the joints, particularly useful in pregnancy and for hypermobility.
• Activity changes: avoid standing on one leg to dress, take stairs one at a time, and keep the knees together when getting in and out of a car.
• Correct leg length differences with a shoe insert if recommended.

Medicines

• NSAIDs such as ibuprofen or naproxen at the label dose, if safe for you, to reduce inflammation. Avoid them in late pregnancy.
• Acetaminophen (paracetamol) as an alternative.
• Short-term muscle relaxants occasionally.
• Biologic or other targeted medicines for inflammatory spondyloarthritis, prescribed by a rheumatologist.

Procedures

• Steroid injection into the SI joint, guided by imaging, can relieve pain for weeks to months and help you progress with therapy.
• Radiofrequency ablation: heat is used to disable the small nerves carrying pain signals from the back of the joint. Relief often lasts 6 to 12 months or more.
• Prolotherapy and platelet-rich plasma injections are offered by some clinics, but the evidence is limited.

Surgery

Minimally invasive SI joint fusion uses implants placed through a small incision to lock the joint. It is considered for people with severe, persistent pain confirmed by diagnostic injections who have not improved after at least 6 months of non-surgical treatment. Trials show meaningful pain relief for many selected patients.

Outlook

Most people with SI joint dysfunction improve within weeks to a few months with exercise, a belt and medicines. Pregnancy-related SI pain usually settles within months after delivery, though some people need ongoing therapy. Pain from arthritis or after lumbar fusion is more likely to be long-lasting, overlapping with chronic back pain, but can be managed with injections, ablation or, occasionally, fusion.

Frequently asked questions

What does SI joint pain feel like?

It is usually a dull ache or sharp pain in the low back and buttock on one side, below the waistline, sometimes spreading to the groin or the back of the thigh. It often hurts when getting up from a chair, climbing stairs, rolling in bed or standing on one leg.

How do I know if my pain is from the SI joint or sciatica?

SI joint pain is centered in the buttock and rarely travels below the knee, and numbness or weakness is uncommon. Sciatica from a slipped disc causes leg pain that is often worse than the back pain, may reach the foot and can cause tingling or weakness. An examination helps tell them apart.

What exercises help sacroiliac joint pain?

Gentle exercises that strengthen the core and buttock muscles help most, such as bridges, clamshells, bird-dogs, pelvic tilts and walking. Gentle stretches for the hips and lower back may ease stiffness. A physical therapist can tailor a program and check your technique so you do not aggravate the joint.

Can sacroiliac joint dysfunction go away?

Yes. Many cases, especially after pregnancy or a strain, improve over weeks to months with physical therapy, a pelvic belt and anti-inflammatory medicine. Pain from arthritis or after spinal fusion can be more persistent, but injections and radiofrequency ablation often help when simple measures are not enough.

When is surgery needed for SI joint pain?

Surgery is considered only when pain is severe, clearly confirmed as coming from the SI joint by numbing injections, and has not improved after at least 6 months of non-surgical treatment. Minimally invasive fusion helps many carefully selected patients. Most people never need surgery.