Quadratus lumborum muscle
The quadratus lumborum muscle is a muscle in the low back. By squeezing the rib cage, spine, and pelvis together, it assists with several motions, including elevating the pelvis and lateral flexion of the spine.
The quadratus lumborum originates from the pelvis and the vertebrae between the pelvis and the rib cage. It attaches to the posterior third of the iliac crest at the top of the pelvis, the transverse processes of the first through fourth lumbar vertebrae, and the iliolumbar ligament.
The quadratus lumborum is innervated by the anterior primary rami (T12-L3).