Quadratus lumborum muscle

The quadratus lumborum is a muscle of the posterior abdominal wall. It is the deepest abdominal muscle and commonly referred to as a back muscle. It is irregular and quadrilateral in shape and broader below than above.Cross-section of the posterior abdominal wall, showing the position of the quadratus lumborum and other muscles.The relations of the kidneys from behind, showing quadratus lumborum at lower left. The quadratus lumborum is a muscle of the posterior abdominal wall. It is the deepest abdominal muscle and commonly referred to as a back muscle. It is irregular and quadrilateral in shape and broader below than above. It originates by aponeurotic fibers into the iliolumbar ligament and the internal lip of the iliac crest for about 5 centimetres (2.0 in). It inserts from the lower border of the last rib for about half its length and by four small tendons from the apices of the transverse processes of the upper four lumbar vertebrae. Occasionally, a second portion of this muscle is found in front of the preceding. It arises from the upper borders of the transverse processes of the lower three or four lumbar vertebræ, and is inserted into the lower margin of the last rib. Anterior to the quadratus lumborum are the colon, the kidney, the psoas major and (if present) psoas minor, and the diaphragm; between the fascia and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves. Quadratus lumborum is a continuation of transverse abdominal muscle.