Home / Conditions / Sacroiliac joint dysfunction
Pain low on one side, beside the base of the spine, that you can point to with one finger. It is often taken for a slipped disc or a hip problem — and a scan alone rarely settles which it is.
The sacroiliac joints are where the sacrum — the triangular bone at the base of the spine — meets the two iliac bones of the pelvis. They pass the weight of the upper body into the legs, and they are built to move very little: a small glide and tilt, held by some of the strongest ligaments in the body.
The ilium is on the left of the picture, the sacrum on the right. The joint runs between them, hidden under the ligaments — dense bands that allow it only a few degrees of movement.
The pain tends to sit just over that joint: low on one side, below the dimple at the back of the pelvis, and spreading into the buttock.
When those ligaments are too loose, or the joint too stiff, it hurts. That is what dysfunction means here — and it is why pregnancy, when the ligaments soften, is a classic trigger.
Sacroiliac joint dysfunction — often shortened to SI joint dysfunction — means pain coming from one of these joints, usually because it is moving too much or too little. It is a recognised source of persistent lower back pain — estimates commonly fall between 15 and 30 percent of people whose pain has lasted beyond a few months — and one of the easier sources to miss, because it borrows the symptoms of its neighbours.
Sacroiliac joint dysfunction and sacroiliitis are not the same thing. Dysfunction describes a joint that hurts because of how it moves. Sacroiliitis means the joint is inflamed — most often as part of an inflammatory condition such as ankylosing spondylitis, and rarely from infection. The symptoms overlap; the causes and the treatment do not.
Pain low in the back and buttock can come from the sacroiliac joint, from a nerve root in the lower spine, or from the hip. Two questions go a long way: can you point to it with one finger? And does it go past the knee, with numbness?
| Sacroiliac joint | Nerve root (e.g. slipped disc) | Hip joint | |
|---|---|---|---|
| Where it hurts most | Low on one side, just below the dimple at the back of the pelvis | The leg, often more than the back | The groin or front of the hip |
| Showing where | One finger, usually | A line down the leg | A cupped hand around the side of the hip |
| Below the knee | Sometimes, but not along a clear line | Often, following one nerve towards the foot | Rarely |
| Numbness or weakness | Not usually | Common, in a defined patch | No |
| Typically worse with | Stairs, standing on that leg, rolling over in bed, getting out of a car | Sitting, bending forward, coughing or sneezing | Walking, putting on socks and shoes |
These are tendencies, not rules, and two can be present at once. Piriformis syndrome — deep buttock pain, worse when sitting — is a fourth mimic. Leg pain that follows a nerve is covered under sciatica.
Numbness, pins and needles or weakness in the leg point towards a nerve, not the joint. If you have them, say so. They change what is examined and what is scanned.
Sacroiliac joint pain is not dangerous in itself. These are the exceptions — and several of them mean the joint is not the cause:
Call us on +65 8849 0677 and describe the symptom. We will see you the same day and arrange imaging if it is needed.
If we are closed, go to an emergency department. We are shut on Sundays and after 1pm on Saturdays. For the third symptom on that list, do not wait for us to open.
Call +65 8849 0677No single scan shows it. Diagnosis builds up from four things, and the last is the most reliable.
Scans mislead in both directions. Wear in the sacroiliac joints is common on the scans of people with no pain at all, and a joint causing real pain can look entirely normal. A report that mentions degenerative change is not, on its own, a diagnosis.
Most people improve without an injection or an operation. Sacroiliac joint treatment is stepped: each tier is for people the one before has not helped enough.
Rest for a day or two at most — longer stiffens the joint and weakens the muscles that support it. Physiotherapy is the backbone of treatment: strengthening the buttock and trunk muscles that stabilise the pelvis, and changing the movements that set it off. Hands-on treatment can ease pain in the short term.
Anti-inflammatories, and heat or ice, for flare-ups. Stronger painkillers have a limited role in short, severe episodes and are not a long-term answer. A sacroiliac belt, worn snugly around the pelvis below the waist, helps most where the joint is moving too much — particularly in pregnancy.
Local anaesthetic with a corticosteroid, placed into the joint under X-ray or CT guidance. The guidance matters: injections given by feel alone often miss this joint. The injection doubles as a diagnostic test, and the relief — anywhere from weeks to several months — is a window in which physiotherapy can make progress.
Where injections confirm the joint as the source but the relief does not last, the small nerves carrying pain from the back of the joint can be treated with radiofrequency heat. Relief often lasts several months to a year. The nerves can regrow, so it may need repeating.
For a small number of people with confirmed joint pain that nothing above has helped. Implants are placed across the joint through a small incision to stop it moving. It is a considered decision, made after diagnostic injections have confirmed the source — not a first step.
With sacroiliac joint pain the question is sharper than usual. The joint sits between the lower spine and the hip, and the three are each other’s commonest mimics.
Pain running down the leg along a line, numbness, pins and needles, weakness — a slipped disc or narrowing pressing on a lumbar nerve root.
A neurosurgeon trains on the nervous system first, so this is the centre of the work. Dr Mathew Tung.
Pain you can point to at the back of the pelvis, or groin pain with a stiff hip.
An orthopaedic surgeon trains on joints, alignment and load first. Dr Lim Heng Hing covers the orthopaedic spine, the hip, and interventional pain management.
You usually cannot tell which before the assessment, and it is common to have more than one. Having both surgeons in one clinic means the answer is not shaped by whichever one you happened to book.
More on how the two differ: neuro spine and orthopaedic spine surgery.
No. Dysfunction is pain from a joint that moves too much or too little. Sacroiliitis is inflammation of the joint, most often part of a condition such as ankylosing spondylitis. They can feel similar, which is why the difference is worth establishing — the treatment is not the same.
Not necessarily. Degenerative change in these joints is common in people with no pain. Whether it explains your symptoms depends on where you hurt and what the examination shows — and, where doubt remains, on a diagnostic injection.
Yes, usually into the buttock and the back of the thigh, and sometimes below the knee. What it rarely does is follow a single clear line to the foot, or cause numbness and weakness. Those point towards a nerve.
Often, yes. Pregnancy hormones loosen the pelvic ligaments so the pelvis can widen for birth, and the sacroiliac joints move more than usual. It commonly settles in the months after delivery. A pelvic belt and physiotherapy help in the meantime.
Very unlikely. Most people improve with physiotherapy and time, and injections or radiofrequency treatment help many of those who do not. Fusion is kept for a small number with confirmed joint pain that nothing else has helped.
No. Bring any X-ray or MRI reports, and be ready to show where the pain is with one finger, whether it goes below the knee, and which movements set it off.
Lower back pain · Back pain · Ankylosing spondylitis · Sciatica · Slipped disc · Piriformis syndrome · Hip pain · Facet joint syndrome
If the pain is low on one side and you can put a finger on it, say so. It changes what gets examined first.
