The sacroiliac joint (SIJ) is a tight joint between the sacrum and the ilium on each side of the pelvis. Anatomically it belongs to the amphiarthroses and allows only a small range of movement.
Its main task is to transfer force between the spine and the lower limbs and to absorb shocks during walking. The SIJ is stabilised by a strong system of ligaments and muscles, including the sacroiliac ligaments and the deep abdominal and trunk muscles.