Where Is the SI Joint? How to Find It on Your Body

Where is the SI joint? You have two of them, one on each side at the back of your pelvis. Each one sits where the sacrum meets the pelvic bone. The sacrum is the flat triangle of bone at the base of your spine.

"SI" is short for sacroiliac. The word joins the sacrum with the ilium, which is the broad, wing shaped top of each pelvic bone. This page helps you find those joints on your own body and understand what they do.

Where is the SI joint on your body

Start with a picture. Your spine ends in the sacrum, which wedges between the two halves of your pelvis like the keystone in an arch. Along each edge of the sacrum, a joint links it to the pelvic bone.

Now find it by touch. Stand and place your hands on the back of your hips, thumbs pointing toward each other. You may feel two small dimples low on your back, just above the buttocks. Many people call them the dimples of Venus. The SI joints sit roughly beneath and a little to the inside of those dimples.

Right at each dimple you can usually feel a small bony bump. That bump is the back edge of the ilium, called the posterior superior iliac spine. The joint lies just to the inside of it, toward the middle. It is deeper than most people expect. You cannot feel the joint itself, only the landmarks around it.

What type of joint is the sacroiliac joint

It is a mixed joint. The front part is a synovial joint, which means it has a small fluid filled gap, like your knee. The back part is packed with short, very strong ligaments that bind the two bones together.

Those ligaments are the main reason the joint moves so little. A few degrees is normal. The joint is built for strength, not for range. Its job is to pass weight between your spine and your legs, and to soften the shock of each step.

Because it moves so little, you will not feel it bend the way you feel your knee bend. You may only notice it when something around it is tired or sore.

Find your SI joints yourself

Here is a short way to sense this area. Take your time and stay within what feels easy.

Stand with your feet about hip width apart. Rest your hands on the back of your pelvis, fingers near the dimples. Now let your weight shift slowly onto your right foot. Notice what your right hand feels. Then shift to your left foot and notice your left hand.

See if you can sense the pelvis tilting a little, and the bones under your fingers changing their angle. Do it again more slowly. Many people find the two sides feel different. One side may feel fuller, or more guarded. You do not need to change anything. You are only noticing.

If standing is uncomfortable, try this lying on your back with your knees bent. Slide your hands under your pelvis, palms down, and gently press one foot into the floor. Then the other. Notice what answers under your hands.

Where SI joint pain is usually felt

Pain from this joint tends to show up in a fairly consistent area. One review describes it as an aching pain below the L5 level, which is the lowest bone of the lower back, often without numbness or tingling. About 15 to 30% of low back pain is attributed to the SI joint, according to a 2021 review in the Journal of Pain Research.

In daily life, people tend to describe it like this:

• Low on one side, just beside the spine, below the belt line.
• Sometimes into the buttock, and now and then the back of the thigh.
• Less often below the knee.
• Often sharper when standing from a chair, rolling over in bed, or standing on one leg.

Many people can point to the spot with one finger. Our guide to sacroiliac joint dysfunction symptoms goes deeper into how that pain feels and what else can look like it.

How this differs from typical low back pain or sciatica

General low back pain can spread more widely across the back, often higher up near the waist. SI joint pain tends to be more local and is often felt more on one side.

Sciatica is different again. It is irritation of a nerve, so it often travels down the leg, sometimes past the knee, and can bring tingling or weakness. SI joint pain more often stays above the knee.

These are tendencies, not rules. A disc, a hip joint, or the deep muscles of the buttock can all produce pain in the same area. Pain location alone is not a diagnosis. A doctor who can examine you is the person who can tell which one you have.

Where gentle Feldenkrais® awareness fits

Once you know where your SI joints are, you have a map. The Feldenkrais Method® uses that kind of map. Its Awareness Through Movement® lessons invite you to move a little at a time, while you watch how the pelvis, ribs and legs join in. Nothing is forced.

Many people find this helps them spot habits, such as always standing on one hip. When the area feels less guarded, daily movement may feel easier. Our Feldypedia entry on chronic lower back pain explains how protective patterns can settle in.

A good first step is the lesson on how to relax your back. It is low effort and done lying down. If you are curious about moves for this area, see our SI joint stretches. If your pelvis feels stuck, read how to unlock your SI joint by yourself first.

Feldy's lessons are short Feldenkrais audio sessions led by a calm voice, made for home practice. You can explore them in the Feldy free trial for 7 days.

Other kinds of help

Gentle awareness work can run next to what your doctor or physical therapist offers. It does not replace an exam, scans or tests when they are needed.

Other movement methods also work with the pelvis. Pilates builds control with graded effort. Yoga uses held shapes and breath. Tai chi uses slow weight shifts. They use different mechanisms, and each has fans for good reasons. Feldenkrais focuses on sensing and learning, with very little load.

When to get checked

Some signs mean you should not wait. See a doctor if pain started after a fall or accident. Get checked for fever, or for night pain with weight loss you cannot explain. Go to the emergency department now for numbness around the groin or inner thighs, new bladder or bowel changes, or leg weakness that keeps growing.

Common Questions about where the SI joint is (FAQ)

Where is the sacroiliac joint located?

It sits at the back of the pelvis, on each side of the sacrum. The sacrum is the triangle of bone below your lowest lumbar vertebra. On each side it meets the ilium, the broad upper part of the pelvic bone. The joint lies just inside the bony bump you can feel at the back of your hip.

Where is SI joint pain usually felt?

Most often low on one side of the back, just beside the spine and below the belt line. It may spread into the buttock and sometimes the back of the thigh. It goes below the knee less often. Because other problems can feel the same, a clinician who examines you is the one who can say what is going on.

What type of joint is the sacroiliac joint?

It is a mix. The front part is a synovial joint, which means it has a small fluid filled space like your knee. The back part is held by very short, strong ligaments. The result is a sturdy joint with only a few degrees of movement.

Which ligaments hold the sacroiliac joint together?

Several thick bands cross it, mainly at the back. The interosseous ligaments sit deep inside the gap between the bones. Other ligaments run to the tailbone and the sitting bone. Together they keep the two sides of the pelvis snug while you walk and stand.

How is SI joint pain different from sciatica?

SI joint pain tends to stay low on one side and in the buttock, with little tingling or numbness. Sciatica is nerve pain that often runs down the leg, sometimes past the knee, and can bring tingling or weakness. The two can overlap, so it helps to have an exam if you are unsure.

When should I see a doctor about pain near the SI joint?

See a doctor soon if pain began after a fall or a collision, if you have a fever, or if night pain comes with weight loss you cannot explain. Go to the emergency department now for numbness around the groin, new bladder or bowel changes, or leg weakness that is growing.