Quadratus lumborum

The quadratus lumborum muscle is a paired, irregular quadrilateral muscle that forms part of the posterior abdominal wall.

  • location: posterior abdominal wall
  • attachments: inferior margin of 12th rib and upper four lumbar transverse processes, iliac crest and iliolumbar ligament
  • blood supply
    • branches of the lumbar arteries
    • other smaller arterial branches, as described below
  • innervation
    • ventral rami of the 12th thoracic nerve
    • L1-L4 spinal nerves
  • action: extension and lateral flexion of vertebral column; fixes 12th rib during inspiration to stabilize the diaphragm
  • origin: medial half of inferior margin of 12th rib and upper four lumbar transverse processes
  • insertion: iliolumbar ligament and internal rim of iliac crest

The muscle is a thick, irregular, quadrilateral-shaped muscle sheet that lies in the posterior abdominal wall on each side of the lumbar vertebrae. It is superficial to the psoas major muscle.

Anterior relations include:

The quadratus lumborum muscle is supplied by:

  • ventral rami of the 12th thoracic nerve
  • L1-L4 spinal nerves

Multiple actions, including:

  • muscle of inspiration
    • fixation of the last rib
    • stabilization of lower attachments of the diaphragm
      • proposed to provide a base for controlled diaphragmatic relaxation to facilitate precise adjustments required for speech and singing 1
  • when one muscle contracts, lateral flexion of vertebral column 
  • when both sides contract, extends the lumbar spine

The extent of attachment to the last rib varies.

Implications in unilateral lower back pain.

May be enlarged in cricket fast bowlers who injure their L4 pars interarticularis 3.

Anatomy: Spine
Anatomy: Abdominopelvic

Anatomy: Abdominopelvic

Article information

rID: 33837
Section: Anatomy
Synonyms or Alternate Spellings:
  • quadratus lumborum muscle

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Cases and figures

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