Quadratus lumborum muscle

The Quadratus lumborum is irregularly quadrilateral in shape, and broader below than above.

Origin and insertion
It arises by aponeurotic fibers from the iliolumbar ligament and the adjacent portion of the iliac crest for about 5 cm., and is inserted into the lower border of the last rib for about half its length, and by four small tendons into 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.

Relations
In front of the Quadratus lumborum are the colon, the kidney, the Psoas major and minor, and the diaphragm; between the fascia and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves.

Variations
The number of attachments to the vertebræ and the extent of its attachment to the last rib vary.

Actions
The quadratus lumborum can perform three actions:
 * 1) Lateral flexion of vertebral column, with ipsilateral contraction
 * 2) Extension of lumbar vertebral column, with bilateral contraction
 * 3) Fixes ribs for forced expiration