Quadratus lumborum muscle

Last revised by Dan Mahon on 11 Jan 2024

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

  • origin: transverse process L5 vertebra, iliolumbar ligament and internal rim iliac crest

  • insertion: transverse processes L1-L4, inferior margin of medial half 12th rib

  • action: extension and lateral flexion of vertebral column; fixes 12th rib during inspiration to stabilize the diaphragm

  • blood supply: branches of the lumbar arteries and other smaller arterial branches, as described below

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

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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