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quadratus lumborum (anatomy)

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Quadratus lumborum is one of the muscles of the posterior abdominal wall. One each side, it originates from the inferior border of the twelfth rib. Descending and broadening, it inserts into the:

  • transverse processes of the first to fourth lumbar vertebrae
  • posterior third of iliac crest
  • iliolumbar ligament in continuity with the iliac crest

It is innervated by the anterior primary rami of spinal nerves T12 to L3.

Quadratus lumborum has several actions:

  • respiration:
    • fixes the twelfth rib in relation to the pull of the diaphragm
    • a muscle of inspiration as it increases the vertical height of the thorax
  • lateral flexion of the trunk upon ipsilateral contraction
  • extension of the lumbar vertebral column upon bilateral contraction