Sacroiliitis and SI Joint Dysfunction: Causes, Examination Tests and Treatment

The pain sits low, just off to one side of your spine, right over the dimple at the top of the buttock. It catches you when you climb the stairs at the metro station, when you step out of an autorickshaw, or when you roll over in bed at night. Standing on one leg to put on your trousers makes you wince. A scan of your lower back was “normal”, or showed a small disc bulge that nobody could quite connect to the pain. Many people in this situation are told it is sciatica or a muscle catch, and months go by.

Very often, the real source is the sacroiliac joint, or SI joint. In an earlier article we introduced facet joint and SI joint pain as hidden causes of back pain. This guide goes deeper into the SI joint alone: what the joint is, the difference between sacroiliitis and SI joint dysfunction, the common causes, the bedside tests doctors use, which scans actually help, and how it is treated, including a fair look at injection options.

What is the SI joint, and why does it hurt?

Your sacrum is the flat, triangular bone at the bottom of your spine. On each side it locks into the large wing of the pelvis (the ilium). Those two meeting points are the sacroiliac joints. Their surfaces are rough and ridged, held together by some of the strongest ligaments in the body, so they behave less like a hinge and more like a firm shock absorber. Every step you take sends force from your upper body, through the SI joints, into the hips and legs.

Because the joint has a rich nerve supply, irritation in the joint lining, the ligaments around it or the bone next to it can all produce pain. Doctors broadly separate two situations:

• Sacroiliitis: true inflammation of the joint. It may show up on MRI as swelling in the bone (bone marrow oedema) and often comes with morning stiffness. Inflammatory arthritis is the classic cause.
• SI joint dysfunction: a mechanical problem. The joint is either too loose (as in pregnancy) or too stiff and overloaded (as with an uneven gait), and the ligaments become strained. Scans usually look normal.

The two can overlap, and both can mimic other problems. That is why the SI joint is often missed in people treated for disc trouble or sciatica.

What causes sacroiliitis and SI joint dysfunction?

Pregnancy and the months after delivery

During pregnancy, hormones such as relaxin loosen the pelvic ligaments so the baby can pass through. The growing bump also shifts your centre of gravity forward. Together these make the SI joints move more than usual, and many women feel pelvic girdle pain at the back of the pelvis. It often eases after delivery, but carrying and feeding a baby, lifting a toddler onto the hip or a difficult labour can keep it going. If the pain shoots down the leg, read our guide to sciatica in pregnancy, as the two are easily confused.

Falls and sudden jolts

Landing hard on one buttock, slipping on a wet bathroom floor, missing a step, or a two-wheeler accident can strain the SI ligaments. So can a sudden unexpected step into a pothole, where one leg drives up into the pelvis. In older adults with osteoporosis, a fall can instead cause a small crack in the sacrum (a sacral insufficiency fracture), which looks like SI pain but needs different care.

Uneven walking and loading

Anything that makes you walk unevenly loads one SI joint more than the other: a painful knee or ankle, hip osteoarthritis, a leg-length difference, a stiff lower back, or simply always carrying a heavy bag or child on the same side. Extra body weight adds to the load, as explained in how extra kilos load your back. People who have had a lower spine fusion operation also put more stress on the SI joints, because the movement that the fused levels lost has to happen somewhere else.

Inflammatory arthritis

Sacroiliitis is often the first sign of ankylosing spondylitis and related conditions (axial spondyloarthritis). It also occurs with psoriasis, inflammatory bowel disease and some infections of the gut or urinary tract. The pattern is different from mechanical pain: it usually starts before the age of 45, comes on gradually, is worse in the second half of the night and in the morning, and eases with movement rather than rest. You can compare patterns in our article on morning joint stiffness.

Infection (rare)

Occasionally bacteria, or in India tuberculosis, settle in one SI joint. This is uncommon but serious. It usually causes severe pain on one side, fever, difficulty bearing weight and raised blood markers. Similar warning signs in the spine are covered in spinal infection and spinal TB.

Symptoms: how SI joint pain behaves

• Location: low back and upper buttock on one side, often just below the belt line. Many people point with one finger to the bony bump beside the dimple.
• Spread: pain can travel into the groin, the back of the thigh and sometimes below the knee, but it rarely causes the tingling, numbness or weakness of a trapped nerve.
• Triggers: climbing stairs, standing on one leg, getting in and out of a car, rolling over in bed, long standing in a queue, and sitting on the painful side.
• Inflammatory clues: morning stiffness lasting more than half an hour, waking in the early hours with pain, alternating buttock pain from one side to the other, and improvement with exercise.

Pain in this area has several possible sources, so it helps to know the look-alikes.

For more on the look-alikes, see piriformis syndrome, trochanteric bursitis and our guide to lower back pain on the right side above the buttocks.

Examination tests for the SI joint, explained simply

No single test proves that the SI joint is the problem. Instead, doctors use a group of “provocation” tests, each of which gently stresses the joint in a different direction to see whether it reproduces your familiar pain. When three or more of these are positive, and the spine and hip have been checked, the SI joint becomes a much more likely source.

• Distraction test: you lie on your back while the doctor presses outwards on the front of both pelvic bones, gently opening the front of the pelvis.
• Compression test: you lie on your side while the doctor presses down on the upper pelvis, squeezing the joints together.
• Thigh thrust: with your hip bent to a right angle, the doctor pushes gently down along the thigh bone, which shears the SI joint on that side.
• Sacral thrust: lying face down, pressure is applied over the sacrum itself.
• Gaenslen’s test: one knee is hugged to the chest while the other leg hangs over the edge of the couch, twisting the pelvis.
• FABER (Patrick’s) test: your foot rests on the opposite knee in a figure-of-four. Pain at the back points towards the SI joint; pain in the groin points towards the hip.

Your doctor will also check reflexes, sensation and leg strength to rule out a trapped nerve, look at how you walk and stand on one leg, and examine the hip. This full picture matters more than any scan.

Imaging and blood tests: what actually helps

• X-ray of the pelvis: can show long-standing sacroiliitis as blurring, erosions or fusion of the joint edges, but these changes take years to appear. A normal X-ray does not rule out early inflammation.
• MRI of the SI joints: the most useful scan when inflammatory sacroiliitis is suspected. Special fluid-sensitive sequences show bone marrow oedema well before the X-ray changes. MRI also picks up a sacral stress fracture or infection. Ask that the SI joints are specifically included, as a routine lumbar spine MRI may not image them fully.
• CT scan: shows bone detail well but uses more radiation, so it is used selectively.
• Blood tests: ESR and CRP (inflammation markers), HLA-B27 if spondyloarthritis is suspected, blood sugar, and vitamin D and B12 levels, which commonly add to aches and slow recovery.

In mechanical SI joint dysfunction, scans are usually normal. That does not mean the pain is imaginary. It means the diagnosis rests on the history and examination, just as it does for many causes listed in our common causes of lower back pain.

Treatment options for SI joint pain

Exercise and pelvic stabilisation

This is the foundation. The SI joint relies on the muscles around it, especially the deep abdominal muscles, the buttock muscles (gluteus maximus and medius) and the pelvic floor, to “close” the joint and keep it stable under load. A good programme starts with gentle activation, then builds to bridges, side-lying leg lifts, single-leg balance and step-ups. Loose joints after pregnancy need stability work; stiff joints often also need mobility work for the hips and lower back. Our articles on physiotherapy for low back pain and exercise for chronic low back pain explain how a progressive plan is built.

Pelvic (SI) belts

A firm belt worn around the pelvis, just below the hip bones rather than at the waist, can make walking and standing more comfortable, particularly during and after pregnancy. It is a support while the muscles get stronger, not a long-term replacement for exercise.

Medicines

Short courses of anti-inflammatory tablets can ease a flare, but they carry stomach, kidney and heart risks with long use, which is one reason painkillers are not the long-term answer. When sacroiliitis comes from ankylosing spondylitis or a related disease, a rheumatologist may prescribe disease-modifying or biologic medicines. These treat the underlying disease, and you should continue them as advised by your doctor. Daily movement is equally important, and our exercises for ankylosing spondylitis routine is a good place to start.

Injection options, fairly explained

If pain persists despite a proper exercise programme, injections may be discussed. Here is what each one involves:

• Diagnostic SI joint block: local anaesthetic placed into the joint under X-ray or ultrasound guidance. If your usual pain clearly eases for a few hours, the joint is very likely the source. It is mainly a test, not a treatment.
• SI joint steroid injection: commonly offered for both inflammatory and mechanical pain. Some people get relief lasting weeks to months; others get little. Steroids reduce inflammation but do not strengthen the ligaments, and repeated doses can raise blood sugar and thin bone, as described in steroid side effects. This is especially relevant for people with diabetes (see why steroid-free care matters in diabetes).
• Radiofrequency treatment of the SI nerves: heat is used to switch off the small nerves carrying pain from the back of the joint. Results vary, relief is temporary as nerves regrow, and it suits only people whose pain was clearly confirmed by diagnostic blocks. Our article on radiofrequency ablation explains the procedure.
• SI joint fusion surgery: considered only for a small group with severe, long-lasting, well-confirmed SI pain after all other care. It is worth getting a second opinion before surgery or injections.

Good questions to ask before any injection: Has the SI joint been confirmed as the source? Will it be done under image guidance? What does it contain? How many times can it be repeated? And what is the plan for strengthening afterwards?

How Dr Heal treats SI joint pain

Our back pain treatment and hip pain treatment teams see many patients whose SI joint was overlooked. A typical plan looks like this:

1. Confirm the source. A detailed history, the SI provocation tests, a nerve and hip examination, and only the scans and blood tests that will change the plan. Our in-house laboratory and radiology at our facilities keep this under one roof.
2. Calm the joint without steroids. When an injection is warranted, our doctors use a regenerative preparation made by Dr Heal Pharma. It contains no steroid, painkiller or antibiotic, and is meant to help the strained ligaments and joint tissues recover rather than simply mask the pain. Read more about regenerative medicine.
3. Look for what keeps it going. Through functional medicine and clinical nutrition we check inflammation, blood sugar, vitamin levels, weight and sleep, and we coordinate with a rheumatologist when inflammatory disease is found.
4. Stabilise the pelvis. A guided rehabilitation programme for the core, buttock and pelvic floor muscles, plus advice on gait, footwear and how you carry loads or your baby.
5. Follow up until you move freely. We review your progress on stairs, standing and sleeping, and adjust the plan step by step.

You can meet our pain specialists or browse all treatments.

What you can do at home

• Take stairs one step at a time with the good leg leading up and the sore leg leading down while pain is high.
• Get into a car or auto with both legs together: sit first, then swing both legs in as one.
• Sleep with a pillow between your knees when lying on your side, and keep your knees together when you roll over.
• Stand evenly. Avoid hanging on one hip in queues or at the kitchen counter, and switch the side you carry a child or bag.
• Keep walking in short, regular spells on flat ground rather than resting for days.
• Try gentle activation: lying on your back with knees bent, tighten your lower tummy and buttocks lightly and hold for ten seconds. Stop anything that sharpens the pain.

Frequently asked questions

Is sacroiliitis the same as SI joint dysfunction?

Not exactly. Sacroiliitis means the joint is inflamed, often from inflammatory arthritis, and may show on MRI. SI joint dysfunction is a mechanical strain from too much or too little movement, and scans are usually normal. The symptoms can look alike.

Can SI joint pain cause pain down the leg?

Yes. It can spread into the buttock, groin and back of the thigh, sometimes below the knee. Unlike nerve pain from a disc, it rarely causes numbness, pins and needles or weakness.

Does sacroiliitis always mean ankylosing spondylitis?

No. Ankylosing spondylitis is a common cause, especially in younger people with morning stiffness, but sacroiliitis can also follow pregnancy, injury, psoriasis, bowel disease or, rarely, infection. Blood tests and an MRI help sort this out.

How long does SI joint pain take to get better?

Mild mechanical strains often settle over a few weeks with activity changes and exercise. Long-standing pain usually needs a structured programme over a few months. Inflammatory sacroiliitis improves once the underlying disease is controlled.

Should I wear an SI belt all day?

Use it during activities that provoke pain, such as long standing or walking, and while the muscles are being strengthened. Relying on it all day for months can let the supporting muscles weaken.

Where can I get SI joint pain treated in Bengaluru?

Dr Heal Pain Cure Hospital assesses and treats sacroiliac joint pain at its HSR Layout and Banashankari branches, both open 24 hours. Patients come from across Karnataka, and our joint pain and arthritis treatment team also cares for inflammatory arthritis.

This article is for general information and is not a substitute for a medical consultation. Please see a doctor for advice about your own symptoms.