Sacroiliac (SI) joint pain, also called sacroiliitis, is a common cause of pain in the low back and buttocks. The sacroiliac joint is the largest joint in the body. The pain is caused by damage or injury to the joint between the spine and hip, and 15-20% of all lower back pain originates from this joint. Sacroiliac pain can mimic other conditions, such as a herniated disc or hip problem. Accurate diagnosis is important to determine the source of pain. Physical therapy, stretching exercises, pain medication, and joint injections are used first to manage the symptoms.
What is sacroiliac joint pain?
The SI joints are located between the iliac bones and the sacrum, connecting the spine to the hips. The two joints provide support and stability, and play a major role in absorbing impact when walking and lifting.
Strong ligaments and muscles support the SI joints. There is a very small amount of motion in the joint for normal body flexibility. As we age our bones become arthritic and ligaments stiffen. When the cartilage wears down, the bones may rub together causing pain (Fig. 1). The SI joint is a synovial joint filled with fluid. This type of joint has free nerve endings that can cause chronic pain if the joint degenerates.
Sacroiliac joint pain ranges from mild to severe. Acute SI joint pain occurs suddenly and usually heals within several days to weeks. Chronic SI joint pain persists for more than three months; it may be felt all the time or worsen with certain activities.
Other terms for SI joint pain include: SI joint dysfunction, SI joint syndrome, SI joint strain and SI joint inflammation.
What are the symptoms?
The signs and symptoms of SI pain start in the lower back and buttock. While the pain is usually one sided, it can also occur on both sides.
Symptoms may worsen with sitting, standing, sleeping, walking or climbing stairs. Often the SI joint is painful sitting or sleeping on the affected side. Some people have difficulty riding in a car or standing, sitting or walking too long. Pain can be worse with transitional movements (going from sit to stand), standing on one leg or climbing stairs.
What are the causes?
The SI joint can become painful when the ligaments become too loose or too tight. This can occur as the result of a fall, work injury, car accident, pregnancy and childbirth, or hip/spine surgery (laminectomy, lumbar fusion).
Sacroiliac joint pain can occur when movement in the pelvis is not the same on both sides. Uneven movement may occur when one leg is longer or weaker than the other, or with arthritis in the hip or knee problems. Autoimmune diseases, such as axial spondyloarthritis, and biomechanical conditions, such as wearing a walking boot following foot/ankle surgery or non-supportive footwear, can lead to degenerative sacroiliitis.