When you feel pain in your lower back or hips, the pain can originate from muscles, soft tissues like tendons and ligaments, or joints.
But it’s not just the joints of the spine or the large hip ball-and-socket that may be the source of the problem—there’s also a pair of joints that can cause symptoms called the sacroiliac (SI) joints.
Watch: Ankylosing Spondylitis Video
The SI joints connect the base the spine with the pelvis on both sides of the body. They’re strong, supportive joints that don’t move much, but they still have the same structure as more common joints in the body, like the knee. This means the SI joints have cartilage, which can degenerate, and synovial fluid, which can become inflamed—causing pain and inflammation in the joint.
Symptoms of SI joint dysfunction and sacroiliitis
Pain in the sacroiliac joint is known as SI joint dysfunction (sometimes also SI joint syndrome, disease, or disorder). Inflammation in the SI joint is known as sacroiliitis.
Regardless of the terms used to describe it, SI joint pain and inflammation cause these symptoms:
- Pain in the lower back, buttocks, hips, and/or groin
- Pain that radiates down the legs (similar to sciatica)
Types of arthritis that can cause SI joint pain
Symptoms in the SI joints can be the calling cards of several types of arthritis, including the following:
Age, excess weight, and repetitive motion can all take a toll on the SI joint’s cartilage, causing it to wear away and bony growths to form and irritate the surrounding tissue.
This form of arthritis causes inflammation where ligaments and tendons attach to bone, which often affects the spine. In fact, SI joint pain is often the first symptom of ankylosing spondylitis.
About 10% of people with psoriasis develop pain and inflammation in their joints, known as psoriatic arthritis.The joints of the spine tend to be affected more, including the SI joints.
Like ankylosing spondylitis and psoriatic arthritis, gout is another inflammatory type of arthritis. Gout often affects just one joint. Most frequently this is the big toe joint, but it can also be in the SI joint.
There are also a few causes of SI joint pain that are not related to arthritis, such as:
- Trauma to the joint
- The relaxing of surrounding ligaments during pregnancy
- Added stress to the joint from another cause or procedure, such as a lumbar spinal fusion
SI joint pain can be confused with many other conditions that cause pain in the lower back and torso, so it’s important to see your doctor for an accurate diagnosis if you are experiencing symptoms.