Quadratus lumborum

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

  • location: dorsal abdominal wall
  • attachments: medial half of inferior margins of 12th ribs and upper four lumbar transverse processes
  • 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 stabilise the diaphragm
  • relations: thick, irregular, quadrilateral-shaped muscle sheet that lies in the posterior abdominal wall
Attachments
  • origin: medial half of inferior margins of 12th ribs and upper four lumbar transverse processes
  • insertion: iliolumbar ligament and internal rim of iliac crest
Relations

The muscle is a thick, irregular, quadrilateral-shaped muscle sheet that lies in the posterior abdominal wall.

Anterior relations:

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
    • stabilisation 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 number and extent of attachments to the last rib vary.

Implications in unilateral lower back pain.

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

Spinal anatomy
Abdominal and pelvic anatomy
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Article information

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

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