Alleviates pain in the lower back. Medical Application Effective relief from Sacroiliac Joint Syndrome, a condition that causes pain in the lower region of the lower back. How it Works The S.I. Back Belt provides stabilization to the hips and sacrum. Design Theory The SI Back Belt is wrapped lower, around the hips, than most back supports. The compression pad combines with a second set of exterior straps to apply effective compression on the sacrum. A non slip gel helps keep the SI Belt in place.