Sacroiliac joint injections are commonly used to help your physician determine the cause of your back pain, but they may not provide you with long-term pain relief. The sacroiliac joint is a large joint in the lower back and buttocks where the pelvis joins with the spine. The joint may cause pain in the lower back, buttocks, abdomen, groin or legs.

A sacroiliac-joint injection places numbing medicine into the joint. The amount of immediate relief will help confirm the joint as a source of pain. Tim-release cortisone also may be injected to help reduce inflammation in the joint.

The sacrum is at the lower end of the spine, just below the lumbar spine. The sacrum is a triangle-shaped bone formed by the fusion of several vertebrae. The sacroiliac joint sits between the sacrum and the iliac bone. You can see these joints from the outside as two small dimples on each side of the lower back at the belt line.