The sacroiliac joint (SI joint) is the joint that connects the iliac bone to the sacrum. The sacrum is the lowest part of the spine and located just above the tailbone. The SI joint is located in the pelvis.
This joint has an important job, which is to help transfer weight between the upper body and the legs. The SI joint also plays an important role in transferring energy between the legs and torso.
In some instances, chronic pain in the lower back is caused by an injury to the sacroiliac joint. An effective treatment option for back pain caused by an injured SI joint is sacroiliac joint fusion. For those who want to learn more about this type of treatment, here are five things to know about SI joint fusion.