The spinal column is made up of small bones (vertebrae) stacked on top of one another, creating the natural curves of the back. Between the vertebrae are flat, round, rubbery pads (intervertebral disks) that act as shock absorbers and allow the back to flex or bend. Muscles and ligaments connecting the vertebrae allow motion while providing support and stability for the spine and upper body. Each vertebra has an opening (foramen) in the center and these line up to form the spinal canal. Protected by the vertebrae, the spinal cord and other nerve roots travel through the spinal canal. Nerves branch out from the spinal column through vertebral openings, carrying messages between the brain and muscles. Facet joints align at the back of the spinal column, linking the vertebrae together and allowing for rotation and movement. Like all joints, cartilage covers the surface where facet joints meet.
The spine contains three segments: lumbar, thoracic and cervical. The lumbar spine consists of five vertebrae (L1-L5) located in the lower back; these are the largest unfused vertebrae in the spinal column, enabling them to carry more of the body's weight. Disks in the lumbar spine are composed of a thick outer ring of cartilage (annulus) and an inner gel-like substance (nucleus). Built for power and flexibility, the lumbar spine supports the entire torso and allows movement such as lifting, twisting and bending. The two lowest segments (including vertebrae and discs) bear the most weight, making them the most susceptible to injury and degradation.
At the bottom of the spine, between the lumbar spine (L5) and the tailbone (coccyx), is a triangular-shaped bone (sacrum) consisting of five segments (S1-S5) that are fused together. The sacrum is connected to the hips, or pelvis (iliac crest), by the sacroiliac joints, which are located on each side of the lower spine. The sacroiliac joints act as shock absorbers, transmitting all the forces of the upper body to the hips and legs. Reinforced by strong, surrounding ligaments, these small joints are very strong and stable, but they do not allow much motion.
Sacroiliac joint dysfunction (SI joint pain) is a painful condition resulting from improper or abnormal movement of the sacroiliac joints. Generally more common in young and middle-aged women, sacroiliac joint dysfunction can cause inflammation of the joints (sacroiliitis), as well as pain that occurs in the lower back, buttocks or legs. Pain can also spread to surrounding muscles, which may spasm in response to the joint dysfunction.
When SI joint pain is the result of too much movement of the joint (hypermobility or instability), pain is typically experienced in the lower back and/or hip, but may also radiate into the groin area. When caused by too little movement of the joint (hypomobility or fixation), the pain usually occurs on one side of the lower back or buttocks, and may radiate down the leg. Although painful symptoms usually remain above the knee, leg pain can be particularly difficult and may extend to the ankle or foot. SI joint pain may feel similar to that of sciatica or a lumbar disc herniation.
SI joint pain is the result of improper movement of the sacroiliac joints, either too much or too little. When the ligaments supporting the sacroiliac joints become loose due to injury, pregnancy or other causes, they may allow too much motion in the joint. Cases of too little movement are often the result of degenerative joint diseases, such as arthritis, that force sacroiliac joints to overcompensate for problems in other nearby joints.
After reviewing your medical history, your physician will ask you to describe how your pain started, where it occurs, and exactly how it feels. Diagnosing sacroiliac joint dysfunction can be difficult because symptoms are often so similar to those of other conditions, such as disc herniation and radiculopathy (pain along the sciatic nerve that radiates down the leg), so it is important to discuss all of your symptoms with your physician. An anesthetic injection block may be applied to the SI joint to assist in diagnosis and provide relief from pain. X-rays and additional imaging studies, such as a magnetic resonance images (MRI), may be recommended to fully assess and diagnose your condition, and to rule out other potential causes for your symptoms.
During a physical examination, your orthopaedic surgeon may use movement of the joint to eliminate other causes and locate the source of your pain. If the motion recreates the symptoms and no other explanation can be found, the sacroiliac joint may be the cause.
Treatment for sacroiliac joint dysfunction is typically conservative, or nonsurgical, and focused on restoring normal joint motion. Typical treatments for SI joint pain include:
In severe cases where pain has not been addressed after several weeks or months of one or more nonsurgical treatments, sacroiliac joint fusion may be an option. During this procedure, one or both of the sacroiliac joints are fused with the goal of eliminating any abnormal motion.
As with any surgery, there are some risks, and these vary from person to person. Complications are typically minor, treatable and unlikely to affect your final outcome. For most people, surgery can provide relief of symptoms and return to function with relatively low risk of complications. Overall, elderly patients have higher rates of complications from surgery, as do patients who are overweight, diabetics, smokers, or suffering from multiple medical problems. Among the general, potential risks associated with surgery are infection, bleeding and blood clots, and reactions to anesthesia. Be sure to discuss the potential risks and benefits with your surgeon prior to surgery.