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 on ...

Pain in your sacroiliac joint is a common cause of low back pain. Sacroiliitis vs. SI joint dysfunction Sacroiliitis is the medical term for inflammation (pain, swelling, and sometimes heat and ...