Iliolumbar ligament sprain happens when the ligament is overstretched. This occurs in the lower back when forcefully bent, arched, or twisted. The iliolumbar ligament is a ligament which goes from the pelvis bone to the lowest vertebra in the thoracic region. The pain occurs deep in the lower back, side of the spine and upper buttocks. Activities which involve any type of arching and twisting in the back will cause pain in the lower back. The iliolumbar ligament sprain will not cause long-term damage If diagnosed properly and doesn’t take more than a number of days to weeks to recover. It is advised to go see a sports physiotherapist if you have any suspicion of this injury.