sacroiliac joint, the joint formed by the sacrum and ilium where they meet on either side of the lower back. The tight joint allows little motion and is subject to great stress as the body’s weight pushes downward and the legs and pelvis push upward against the joint. The sacroiliac joint must also bear the leverage demands made by the trunk of the body as it turns, twists, pulls, and pushes. When these motions place an excess of stress on the ligaments binding the joint and on the connecting muscles (such as during weightlifting), strain may result.
