The sacroiliac joint sits between the sacrum and the iliac bones of the lower back, in the area where the spine meets the pelvis. They are weight bearing structures and are subject to mechanical stress.
The sacroiliac joints have cartilage and are lubricated with synovial fluid that is kept within the joint by a surrounding capsule. The joints are reinforced by a dense network of ligaments that surround the joint and help enhance its stability.
The joint does move albeit a very small amount compared to other joints in the spine. The sacroiliac joints have a rich nerve supply (sacral lateral branches and lumbosacral plexus) that allows it to perceive pain when injured.
Mechanical stress to the joint can lead to injury and pain. Common causes of such stress include aging, lumbar fusion, injury, inflammatory conditions or repetitive abnormal loading of the joints over time.
The joint will show changes of thinning or loss of the articular cartilage, reduction or loss of the synovial fluid or lubricant, roughening and overgrowth of bone, inflammation in the bone adjacent to the joint space, overgrowth of the joint and, at times, cysts can develop in the bone adjacent to the joint space.
The joint is then said to have developed arthritic changes or osteoarthritis. These arthritic changes can produce spine pain. This condition may also be referred to as "sacroiliac joint syndrome or dysfunction."
Certain types of inflammatory arthritis can more commonly affect the sacroiliac joint such as ankylosing spondylitis or psoriatic arthritis. Additionally, the ligaments on the back portion of the joint can be subject to injury and become painful.
Patients with sacroiliac joint pain have primary pain and stiffness in their buttock, hip and lowest most portion of the lower back.
At times sacroiliac joint pain can be felt in the thigh or groin.
Motion or increased stress to the joints such as in standing or sitting on the side of pain, usually increases pain caused by these joints.
The diagnosis of sacroiliac joint syndrome begins with a complete history and physical exam.
X-rays can show arthritis in the joints but a CT scan or MRI can show greater detail of the joint’s anatomy. Though, imaging is often “normal” and cannot rule out sacroiliac joint pain.
A bone scan can occasionally be helpful to determine if there is substantial joint inflammation.
The best method to determine if the sacroiliac joint is causing pain is to perform diagnostic injections of anesthetic under x-ray (fluoroscopic) guidance.
The best diagnostic test to determine if joint is the source of pain is to numb the inside of the joint surface via a sacroiliac joint injection under x-ray guidance.
The best diagnostic test to determine if the back (posterior) portion of the joint and overlying ligaments is the source of pain is to numb the sacral lateral branches under x-ray guidance.
The first treatments should be non-invasive and include such methods as postural correction, activity alteration, improving muscle flexibility, strengthening, restoring normal joint motion, bracing in an attempt to limit joint motion and medications to reduce inflammation.
Commonly such treatments are performed by physical therapists, manual medicine providers, and massage therapists. Acupuncture has also been tried with success in a subset of patients.
When these more conservative treatments fail then fluoroscopically guided interventions can be considered.
Sacroiliac joint injections involve placing anti-inflammatory corticosteroid agents into the joint to reduce joint inflammation, irritability and hopefully pain.
Post injection rehabilitation methods are often reinstituted in hopes of synergistic effects occurring from a combined care approach.
If sacroiliac joint injections fail to provide relief then lateral branch blocks can be performed as the ideal prognostic test to determine if the more advanced care option of radiofrequency neurotomy should be considered.
Radiofrequency neurotomy (aka radiofrequency ablation or RFA) involves melting the lateral branches so one no longer feels pain from a majority of the joint and ligaments.
The pain signals are essentially short circuited or blocked for a long period of time (e.g. 10 months or longer). If the nerves regenerate and the pain signals are restored the procedure can often be repeated to reinstate pain relief.
In a very small subset of patients who fail to respond to all other treatment options, including radiofrequency neurotomy, then a fusion of the sacroiliac joint may be cautiously considered.