Sacroiliac (SI) joint blocks are injections that are primarily used for diagnosing and treating the low back pain associated with sacroiliac joint dysfunction. The SI joint lies next to the spine and connects the sacrum (bottom of the spine) with the pelvis (hip).

In an SI joint block injection approach, a physician uses fluoroscopic guidance (live x-ray) and inserts a needle into the sacroiliac joint to inject lidocaine (a numbing agent) and a steroid (an anti-inflammatory medication). It takes a highly skilled and experienced physician to be able to insert a needle into the sacroiliac joint.

An SI joint block injection may be repeated up to three times per year. For the treatment to be successful, the injection should be followed by physical therapy and/or chiropractic manipulations to provide mobilization and range of motion exercises.