The sacroiliac joint (SIJ) connects the sacrum to the ilium on the left and right sides of the spine. Thus, humans have a left and right sacroiliac joint. The SIJ is not very mobile and is stabilized by several ligaments. It transfers the forces that come from the spine to the pelvis and the lower extremities.

Due to incorrect and overloading, a SIJ blockage can occur. This is a mechanical disturbance in the joint itself, which prevents it from functioning properly. In the case of a SIJ blockage, often only one side is affected. The blockage often also incorrectly and overloads the surrounding structures, which can cause radiations into the back and legs. However, pain in the sacroiliac joint can also occur without an underlying SIJ blockage.