Sacroiliitis is inflammation of the sacroiliac (SI) joint in the pelvic region of your body. This can lead to symptoms of pain in the lower back and buttocks. Sacroiliitis can be caused by several ...

Your SI joint, or sacroiliac joint, connects your sacrum (otherwise known as the tailbone) and your illiac, the bone of the topside of your pelvis. Technically, there's two of these joints—one ...