Sacroiliac Joint (SI Joint) Anatomy

The sacroiliac joint (SI joint) is located in the pelvis; it links the iliac bones (pelvis) to the sacrum (lowest part of the spine above the tailbone). It is an essential component for energy transfer between the legs and the torso.

The SI joint is the link between the ilium in the pelvis to the sacrum, which is the lowest part of the spine above the tailbone.

Like any other joint in the body, the SI joint can be injured and/or undergo degeneration. When this happens, people can feel pain in their buttock and sometimes in the lower back, hips and legs. This is especially true while lifting, running, walking or even lying on the involved side.

Excessive motion in the SI joint may inflame and disrupt the joint and surrounding nerves causing pain in the lower back, hip, groin, or pelvis.

It’s common for pain from the SI joint to feel like disc or lower back pain, or sometimes hip or groin pain. For this reason, SI joint disorders should always be considered in lower back, hip, and pelvic pain diagnosis.

Symptoms

• Lower back pain
• Sensation of low extremity: pain, numbness, tingling, weakness
• Pelvis/buttock pain
• Hip/groin pain
• Feeling of leg instability (buckling, giving way)
• Disturbed sleep patterns due to pain
• Disturbed sitting patterns (unable to sit for long periods, sitting on one side)
• Pain going from sitting to standing

SI joint pain can mimic pain in the lower back, hip, groin, or pelvis. Patients who suffer from SI joint dysfunction can have severe pain when performing transitional movements like standing from a chair. Patients who have SI joint pain usually find it difficult to sit for long periods of time, and usually try to alleviate the discomfort by sitting on the least effected side.

Making a Diagnosis

A variety of tests performed during physical examination may help reveal the SI joint as the cause of your symptoms. Sometimes, X-rays, CT-scan or MRI may be helpful in the diagnosis of SI joint-related problems because they can rule out other common sources of pain—such as your lumbar spine or hip joints. It is also important to remember that other conditions (like a disc problem) can co-exist with SI joint disorders.

The most relied upon method to accurately determine whether the SI joint is the cause of your lower back pain symptoms is to inject the SI joint with a local anesthetic. This diagnostic injection will be performed under either X-ray or CT guidance to verify accurate placement of the needle in the SI joint. If your symptoms decrease by at least 50%, it can be concluded that the SI joint is either the source of or a major contributor to your lower back, hip, or pelvic pain. If the level of pain does not change after SI joint injection, it is less likely that the SI joint is the cause of your pain.