In short
The sacroiliac joints connect the base of the spine to the pelvis. SI joint pain is usually felt in the buttock and lower back on one side, and can spread into the thigh. It’s common in pregnancy and with some types of arthritis, and usually responds to exercise and physiotherapy.
On this page
What is the sacroiliac joint?
You have two sacroiliac (SI) joints, one on each side, where the base of the spine (the sacrum) meets the pelvis. They move only a little, and their job is to transfer load between the upper body and the legs.
Symptoms of SI joint pain
- Pain in the buttock and lower back, usually on one side, below the belt line
- Pain that can spread into the back of the thigh, and occasionally below the knee
- Pain when standing on one leg, climbing stairs, getting in and out of a car, or rolling over in bed
- Pain after sitting for a long time
These symptoms overlap with other lower back and hip problems, so SI joint pain can be hard to tell apart without an assessment.
Pain that isn’t settling?
Talk it through with an Australian doctor online. No referral needed.
What causes it?
- Pregnancy. Hormonal changes and extra load make the pelvic joints more mobile. See pelvic girdle pain.
- Injury, such as a fall onto the buttock or a sudden jolt.
- Repetitive load, including running and some sports.
- Inflammatory arthritis. Sacroiliitis, inflammation of the SI joints, is a feature of axial spondyloarthritis. It typically causes morning stiffness lasting more than 30 minutes that improves with movement, often starting before the age of 45.
- Previous spinal fusion, which can increase load on the SI joints.
How is it diagnosed?
A doctor or physiotherapist will ask about your symptoms and use specific examination tests that stress the joint. No single test is reliable, so several are usually combined. If inflammatory arthritis is suspected, blood tests and imaging, often an MRI, can help. In some cases, an injection of local anaesthetic into the joint is used to confirm the source of pain.
Treatment
- Exercise and physiotherapy, focusing on strengthening the hips, buttocks and core, are the first step.
- A pelvic support belt helps some people, particularly in pregnancy.
- Activity changes, such as avoiding long periods of sitting and splitting stairs into smaller steps for a while.
- Procedures. Joint injections and other procedures are options for some people with ongoing pain. Your GP can refer you if these are worth considering.
- Inflammatory arthritis is treated differently, usually with a rheumatologist’s involvement.
When to see a GP
See a GP if buttock or lower back pain lasts more than a few weeks, comes with long morning stiffness, or is affecting your sleep or daily life. Urgent signs, such as numbness around the groin or bladder changes, need emergency care.
Next step: talk to a doctor
Answer a few quick questions and you’ll get an email about your eligibility. A consultation doesn’t guarantee any particular treatment.
References
- Cohen SP, Chen Y, Neufeld NJ. Sacroiliac joint pain: a comprehensive review of epidemiology, diagnosis and treatment. Expert Rev Neurother. 2013;13(1):99-116.
- Vleeming A, Albert HB, Ostgaard HC, et al. European guidelines for the diagnosis and treatment of pelvic girdle pain. Eur Spine J. 2008;17(6):794-819.
- Hartvigsen J, Hancock MJ, Kongsted A, et al. What low back pain is and why we need to pay attention. Lancet. 2018;391(10137):2356-2367.
- healthdirect. Back pain.
This guide is general information, not medical advice. It doesn’t replace a consultation with a doctor who knows your history. In an emergency, call 000.