The sacroiliac joint or SI joint is the joint in the bony pelvis between the sacrum and the ilium of the pelvis, which are joined together by strong ligaments. In humans, the sacrum supports the spine and is supported in turn by an ilium on each side. The joint is a strong, weightbearing synovial joint with irregular elevations and depressions that produce interlocking of the two bones. The human body has two sacroiliac joints, a left and a right joint, that often match each other but are highly variable from person to person.
- Mechanical SIJ dysfunction usually causes a dull unilateral low back pain ache. The pain is usually no more than a mild to moderate ache around the dimple or posterior superior iliac spine (PSIS) region. The pain may become worse and sharp while doing activities such as standing up from a seated position or lifting the knee up to the chest during stair climbing.
- The pain typically is felt on one side or the other (unilateral pain) but occasionally can be bilateral.
- When the pain of SIJ dysfunction is severe, there can be referred pain into the hip, groin and occasionally down the leg, but rarely below the knee.
- Pain can be referred from the SIJ down into the buttock or back of the thigh, but rarely to the foot.
- Low back pain and stiffness, often unilateral, that often increases with prolonged sitting or prolonged walking.
- Pain may occur during sexual intercourse; however, this is not specific to just sacroiliac joint problems.
- Occasionally there may be referred pain into the lower limb, which can be mistaken for “true” sciatica from a herniated lumbar disc. This often can be differentiated from radicular (true nerve root pain) with a clinical test called the straight leg raising (SLR) test. This test, when negative, “rules out” > 90% of patients with true radicular pain from a nerve root compression like a disc herniation/protrusion.
Facet Rhizotomy and Sacroiliac Joint Block Injections: In this injection procedure a needle with a probe is inserted just outside the joint. The probe is then heated with radio waves and applied to the sensory nerve to the joint in order to disable the nerve.Theoretically, by deadening the sensory nerve to the facet joint, a facet rhizotomy effectively prevents the pain signals from getting to the brain. A facet rhizotomy injection is successful in providing lasting pain relief for approximately 50% of patients.