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Sacroilliac Joint Dysfunction

The sacroiliac (SI) joints are formed by the connection of the sacrum (or “tailbone”) and the right and left iliac bones (commonly known as pelvic bones). As a result, the SI joints connect the spine to the pelvis by a collection of strong ligaments. These joints support the weight of the upper body when we are erect, which places a large amount of stress across them. This can lead to wearing of the cartilage and arthritis.

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What to know about SI dysfunction

There are many different terms for sacroiliac joint problems, including SI joint dysfunction, SI joint syndrome, SI joint strain, and SI joint inflammation. Each of these terms refers to a condition that causes pain in the SI joints from a variety of causes.


There are many different causes of SI joint pain, including pregnancy, limb-length discrepancy or difference in leg length. I some cases, an exact cause leading to a painful SI joint condition cannot be found.

The SI joint, similar to all joints in the body, can be affected by different types of arthritis, including rheumatoid arthritis, gout, and psoriasis. The joint can also be infected in a condition called septic arthritis when bacteria that travel in the blood settle in the joint.

Injury to the SI joint is also thought to be a common cause of pain such as during a fall or a motor vehicle accident.


The most common symptoms from SI joint dysfunction are low back and buttock pain, which may affect one side or both SI joints. The pain can radiate down the leg all the way to the foot or may radiate into the groin area. People often feel muscle spasm in one or both of their buttocks muscles.

Problems with the SI joint may make sitting difficult. Pain in one SI joint may cause a person to sit with that buttock tilted up. It is usually uncomfortable to sit flat in a chair.


Diagnosis begins with a complete history and physical exam to distinguish pain coming from the SI joint from pain coming from other spine conditions. Blood and/or urine workup may be ordered if there is any question whether you might have an infection or some type of arthritis affecting multiple joints. X-rays are commonly ordered of both the low back and pelvis. X-rays of the lumbar spine and hips are helpful to rule out problems in these areas that may act and look like SI joint dysfunction.

Magnetic resonance imaging (MRI) scan can be used to look at the lumbar spine and pelvis in much more detail and to rule out other causing the symptoms. A computed tomography (CAT) scan may also be used to show a much more detailed look at the bone of the pelvis and the sacroiliac joint.

A bone scan is useful to see how the skeleton is reacting to any type of “stress,” such as an injury, an infection, or inflammation from arthritis.

The most accurate way of determining whether the SI joint is causing pain is to perform a diagnostic injection of the joint. Because the joint is so deep, this must be done using X-ray guidance with a fluoroscope (a type of realtime X-ray). Once the doctor places a needle in the joint, an anesthetic is injected into the joint to numb the joint. If your pain goes away while the anesthetic is in the joint, then your doctor can be reasonably sure that the pain you are experiencing is coming from the SI joint.