The
sacroiliac joint or
SI joint (SIJ) is the
joint in the bony pelvis between the
sacrum and the
ilium of the
pelvis, which are joined by strong
ligaments. In humans, the sacrum supports the
spine and is supported in turn by an ilium on each side. The joint is a strong, weight transferal
synovial plane joint with irregular elevations and depressions that produce interlocking of the two bones. The human body has two sacroiliac joints, one on the left and one on the right, that often match each other but are highly variable from person to person.