SI joint pain comes from the sacroiliac joints, where the base of your spine meets your pelvis. It usually sits LOW in the back, on one side, just over the bony dimple at the top of the buttock.
It’s more common than many people think. In people with long-lasting low back pain, the SI joint is the main source in up to about 1 in 4.
Exercise-based physio is the first treatment, and most people improve with it. Injections and surgery exist for pain that won’t settle, but the evidence for them is thinner, and the diagnosis needs to be confirmed first.
Where SI joint pain is felt
- One side, low down. Pain sits at or just below the dimple at the top of the buttock. Pointing to that exact spot with one finger is a classic sign
- Into the buttock and thigh. It can spread into the groin or down the back of the thigh. It usually stays above the knee, though it can travel further
- Worse with certain moves: standing on one leg, climbing stairs, rolling over in bed, getting in and out of a car, long spells of sitting or standing, or lying on that side
- Usually no pins and needles. Numbness, tingling or pain shooting down to the foot points more toward a trapped nerve in the spine. See sciatica
Who gets it
- Pregnancy and after birth. Hormones loosen the joints to allow for childbirth, and the extra weight changes how you walk
- A fall or jolt, such as landing hard on your buttock or a car accident
- Arthritis, both wear-and-tear and inflammatory types such as ankylosing spondylitis
- After a lower back fusion. The SI joints below the fused bones can take extra strain. See spinal fusion recovery
- Women more than men, partly because the joints move a little more
How SI joint pain is diagnosed
There’s no single test. X-rays and scans often look normal, or show changes that people without pain have too.
- Your pain map and story. Where it hurts and what sets it off narrows things down fast
- Provocation tests. Your physio or doctor presses on or stretches the joint in several ways. If three or more of these reproduce your usual pain, the SI joint is a likely source
- Ruling out the spine and hip. Disc problems and hip arthritis can hurt in the same area. See hip arthritis
- A numbing injection. If pain doesn’t settle, a doctor may inject local anesthetic into the joint using X-ray guidance. If your usual pain mostly goes for a few hours, that points to the SI joint
- Blood tests or an MRI if an inflammatory arthritis is suspected, especially in younger people with long morning stiffness that eases as they move
Most SI joint pain needs calming down and strengthening, not fixing.
What helps
- Exercise-based physio. The best evidence is for a program that strengthens your hips, buttocks and trunk. Improvement builds over weeks to months
- Hands-on treatment plus exercise. Manipulation or mobilization of the joint can ease pain in the short term, and does better combined with exercise than on its own
- An SI belt. A support belt worn low around the hips can help, especially during and after pregnancy
- Change what flares it. Sit with your weight even on both buttocks, sit down to put on shoes and pants, and get into the car bottom first, then swing both legs in together
- Sleep with a pillow between your knees if you lie on your side
- Pain relief: ice or heat, whichever feels better, and anti-inflammatory painkillers if your pharmacist says they’re safe for you
Injections and nerve treatments
- Steroid injection into the joint. Some people get relief for weeks to months. Research results are mixed, so treat it as a way to make exercise possible, not as a cure. See how long a cortisone shot lasts
- Radiofrequency ablation. A needle heats the small nerves that carry pain from the joint. It’s usually only offered if a numbing injection clearly helped first. Some people get useful relief, but results vary and it may need repeating
What about SI joint fusion?
Fusion surgery fixes the joint with metal implants so it can no longer move. It’s usually done through a small cut, with the implants placed across the joint using X-ray guidance.
- It’s a last resort. It’s meant for people whose diagnosis has been confirmed, usually with a numbing injection, and whose pain has lasted many months despite good nonsurgical care
- The evidence is promising but limited. Trials in carefully chosen people suggest pain and daily function improve more than with ongoing nonsurgical care. The research base is still small, and not everyone gets relief
- Ask how the diagnosis was confirmed if fusion is suggested, and consider a second opinion if it wasn’t
Go to the emergency department now if
These aren’t SI joint problems. They can be signs of cauda equina syndrome, where the nerves at the bottom of the spine are badly squashed. It’s rare, but it needs hospital treatment the same day.
- New trouble peeing, not being able to pee, or leaking pee or poo without knowing
- Numbness around your genitals, buttocks or inner thighs, the area that would touch a saddle
- Weakness or numbness in BOTH legs
Get it checked if
- The pain started after a fall or accident, especially if you’re older or have thin bones
- You have a fever or feel unwell with it. Infection in the joint is rare but serious
- You’re under 45 with long morning stiffness in your back or buttocks that eases as you move. That can be an inflammatory arthritis, which can inflame the SI joints and needs its own treatment
- There’s no improvement after 6 to 8 weeks of regular exercise
- You have weight loss you can’t explain or a history of cancer
Confirm it before you inject it, and strengthen it before you fuse it.