<P> The sacroiliac joint or SI joint ( SIJ ) is the joint between the sacrum and the ilium bones of the pelvis , which are connected 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 transferral 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 . </P>
the joint between a coxal bone of the pelvis and the sacrum
sacroiliac joint