Sacroiliac (SI) joint dysfunction is a common cause of low back pain. Other terms for this condition include sacroiliitis, SI joint inflammation, SI joint syndrome, and SI joint strain.

This condition can make it hard for you to do daily activities, such as sitting, standing, walking, and even sleeping.

In fact, the sacroiliac joints are the primary source of pain in 5% to 10% of all patients with low back pain.¹ But many patients with SI joint pain spend months—even years—without a correct diagnosis.

That’s because sacroiliac joint dysfunction is sometimes difficult to diagnose. Since the SI joints are so close to your hip bones and lumbar spine (low back), it’s common for SI joint dysfunction to be mistaken for other causes of low back pain, such as a herniated or bulging disc.

Anatomy of the Sacroiliac Joint
SI joints are weight-bearing joints—like your knees. But unlike your knees, your SI joints are buried very deep, behind layers of muscles and tissues.

You have 2 SI joints—one on the left side and one on the right side of your pelvis.

These L-shaped joints connect your sacrum and your right and left iliac bones, the 2 large bones that form your pelvis. Your sacrum is formed by 5 fused vertebrae just below your low back. Unlike other vertebrae in your spine, the vertebrae in your sacrum don’t move.

Even though your SI joints are small, they’re actually very strong because they help distribute weight from your upper body to your legs.

Ligaments and cartilage are also important parts of your SI joints. The ligaments in your SI joints are some of the strongest ligaments in your body.

Also, like other joints in your body, your SI joints have cartilage that acts as a shock absorber between your bones and allows for some movement.

Symptoms of Sacroiliac Joint Dysfunction
If you have low back pain, it can be extremely difficult for your doctor to determine the exact source of your pain at first. However, there are a few key symptoms of sacroiliac joint dysfunction you should know.

The main symptom of sacroiliac joint dysfunction is low back pain. But SI joint dysfunction can also cause pain in your hips, buttocks, thighs, or groin.

Sometimes, SI joint pain can be so severe that just pressing on the area hurts.

Other symptoms of sacroiliac joint dysfunction include:

• Pain while doing daily activities such as climbing stairs or getting up from a chair
• Pain that is aggravated by standing or walking for long periods of time, but that improves when you’re lying down
• Stiffness or burning sensation in your pelvis

Causes of Sacroiliac Joint Dysfunction
Multiple conditions can cause SI joint dysfunction. The most common are:

• Arthritis: SI joint dysfunction can be caused by spondylosis (spinal osteoarthritis)—when your cartilage around your SI joints wears down, your bones can start to rub against each other. Anklylosing spondylitis, a type of inflammatory arthritis that affects your spine, can also cause SI joint dysfunction.
• Pregnancy: Many pregnant women experience low back pain or pelvic pain due to sacroiliac joint dysfunction because the SI joints can stretch and become loose during pregnancy. Also, hormone changes and the additional weight gained during pregnancy can put added stress on SI joints.
• Trauma: A sudden impact like a car accident or bad fall could damage your SI joints.
• Infection: Infection is extremely rare, but it is another possible cause of SI joint dysfunction.

Although SI joint dysfunction may be very painful, keep in mind that there are many treatment options that can help reduce or even prevent your low back pain.