Quadratus lumborum muscle

Last revised by Dr Calum Worsley on 02 Jun 2021

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 muscles contract, extension of the lumbar spine
  • 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

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Cases and figures

  • Case 1a: labeled 20
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  • Case 1b: labeled 101
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  • Case 1c: labeled 99
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  • Figure 1
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  • Figure 2
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  • Figure 3
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