Musculus quadratus lumborum

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

Summary

  • 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

Gross anatomy

Attachments
  • origin: medial half of inferior margin of 12th rib 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 on each side of the lumbar vertebrae. It is superficial to the psoas major muscle.

Anterior relations include:

Arterial supply

The quadratus lumborum muscle is supplied by:

Innervation

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

Action

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
  • when one muscle contracts, lateral flexion of vertebral column 
  • when both sides contract, extends the lumbar spine

Variant anatomy

  • extent of attachment to the last rib varies

Related pathology

  • implications in unilateral lower back pain
  • may be enlarged in cricket fast bowlers who injure their L4 pars interarticularis