The sacroiliac joints (SIJ) are a pair of structures (on the right and left) that connect the spine to the pelvis and allow for motion. They are weight-bearing joints as the weight from the upper body is transmitted down the spine, through the sacroiliac joints, and into the pelvis, hips, and lower extremities. Like other joints in the body, the sacroiliac joints are surrounded by a capsule that contains a lubricating fluid. SI joint motion allows us to walk upright, to lift, and to carry.
The sacroiliac joint is supported by many muscle groups and ligaments with a dense mix of free nerve endings and spinal nerve roots. When there is inflammation to the sacroiliac joint, the abundance of these nerves become irritated, and patients experience intense low back pain. Patients typically complain that sacroiliac joint pain worsens when sitting for long periods or performing twisting motions. These issues usually correct themselves with exercise.
Sacroiliac Joint Disease
Sacroiliac joint disease is one of the major causes of low back, buttock, groin, and lower extremity pain. It has been estimated to affect between 15 to 38% of the general population.
The most common painful condition of the sacroiliac joint is known as sacroiliac joint dysfunction, which is often caused by direct impact on the buttocks, motor vehicle accidents, or other sports-related injuries. It can also be caused by arthritis, infection, or simply as the result of age-associated degeneration. When sacroiliac join dysfunction occurs, there is a structural change within the joint with the nearby pelvic and/or sacral bones that induces pain in cartilage or ligaments.
The sacroiliac joint is often overlooked as a source of low back pain, especially since diagnosis is challenging. Further complicating diagnosis is the fact that the SI joint can receive pain generated from other locations. As a result, the diagnosis of SI joint dysfunction usually occurs after excluding other possibilities.
One of the most effective procedures to confirm a diagnosis of SI joint pain is through an injection into the joint to cause a reaction and reproduce the painful symptoms. If the symptoms are reproduced, and the SI joint as a source of the pain is confirmed, the diagnostic injection can be followed with a therapeutic injection for pain relief.