Main Model
23 Quadratus lumborum
The quadrilateral quadratus lumborum forms a thick muscular sheet in the posterior abdominal wall. It lies adjacent to the lumbar transverse processes and is broader inferiorly. Close to the 12th rib, the lateral arcuate ligament crosses the quadratus lumborum. The subcostal nerve passes posterior to this ligament and runs inferolaterally on the quadratus lumborum. Branches of the lumbar plexus run inferiorly on the anterior surface of this muscle.
Origin: Medial half of inferior border of 12th ribs and tips of lumbar transverse processes
Insertion: Iliolumbar ligament and internal lip of iliac crest
Innervation: Anterior branches of T12 and L1-L4 nerves
Main Action(s): Extends and laterally flexes vertebral column; fixes 12th rib during inspiration