Sacroilliac Joint Dysfunction

(SI Joint Pain)

The sacroiliac (SI) joints are formed by the connection of the sacrum and the right and left iliac bones. The sacrum is the triangular-shaped bone in the lower portion of the spine, below the lumbar spine. While most of the bones (vertebrae) of the spine are mobile, the sacrum is made up of five vertebrae that are fused together and do not move. The iliac bones are the two large bones that make up the pelvis. As a result, the SI joints connect the spine to the pelvis. The sacrum and the iliac bones (ileum) are held together by a collection of strong ligaments. There is relatively little motion at the SI joints. There are normally less than 4 degrees of rotation and 2 mm of translation at these joints. Most of the motion in the area of the pelvis occurs either at the hips or the lumbar spine. These joints do need to support the entire 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 of the SI joints and arthritis.

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.


What causes this problem?

There are many different causes of SI joint pain. Pregnancy may be a factor in the the development of SI joint problems later in life. Also, if a person has one leg is shorter that the other, the abnormal alignment may end up causing SI joint pain and problems. Often, an exact cause leading to a painful SI joint condition can't be found. The joint simply gets painful, and the patient and provider don't have an answer as to why the joint has become painful.

The SI joint is a synovial joint, similar to all joints such as the knee, hip and shoulder. Because of this, different types of arthritis that affect all the joints of the body will also affect the sacroiliac joint. This includes conditions such as rheumatoid arthritis, gout and psoriasis. The joint can be infected when bacteria that travel in the blood settle in the joint causing a condition called septic arthritis. This is perhaps the most worrisome cause of SI joint pain and may well require surgery to drain the infection.

Injury to the SI joint is thought to be a common cause of pain. Injury can occur during an automobile accident. One common pattern of injury occurs when the driver of a vehicle places one foot on the brake before a collision. The impact through the foot on the brake is transmitted to the pelvis causing a twisting motion to this side of the pelvis. This can injure the SI joint on that side resulting in pain. A similar mechanism occurs with a fall on one buttock. The force again causes a twisting motion to the pelvis and may injure the ligaments around the joint.


The most common symptoms from SI joint dysfunction are low back and buttock pain. The pain may affect one side or both SI joints. The pain can radiate down the leg all the way to the foot and may be confused with a herniated disc in the lumbar spine. The pain 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.  Your doctor will ask questions about your symptoms and how the pain is affecting your daily activities. Your doctor will also want to know what positions or activities make your symptoms worse or better. You will be asked about any injuries in the past and about any other medical problems you might have such as any arthritis that runs in the family.

Your doctor then examines you by checking your posture, how you walk and where your pain is located. Your doctor checks to see which back movements cause pain or other symptoms. Your skin sensation, muscle strength, and reflexes are also tested because it is difficult to distinguish pain coming from the SI joint from pain coming from other spine conditions.

Laboratory tests may be ordered if there is any question whether you might have an infection or some type of arthritis affecting multiple joints. You may also need to have blood drawn and give a urine sample to send to the laboratory for special tests.

X-rays are commonly ordered of both the low back and pelvis. X-rays can give your doctor an idea about how much wear and tear has occurred in the SI joint. X-rays of the lumbar spine and hips are also helpful to rule out problems in these areas that may act and look like SI joint dysfunction.

Other radiological tests may be useful as well. The 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 conditions in the area. The MRI scan uses magnetic waves rather than x-rays and shows a very detailed picture of the soft tissues of the body.

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. This test involves injecting chemical "tracers" into your blood stream. The tracers then show up on special spine X-rays. The tracers collect in areas where the bone tissue is reacting strongly to some type of stress to the skeleton, such as arthritis and infection of the SI joint.

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.

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