Quadratus Lumborum

Written by Aren Mnatzakanian

Last updated January 5, 2023 • 3 Revisions •

The quadratus lumborum is a muscle of the posterior abdominal wall. It is a thick muscular sheet, quadrilateral in shape, and positioned superficial to the psoas major.

  • Attachments: Originates from the iliac crest and iliolumbar ligament. The fibres travel superomedially, inserting onto the transverse processes of L1 – L4 and the inferior border of the 12th rib.
  • Actions: Extension and lateral flexion of the vertebral column. It also fixes the 12th rib during inspiration, so that the contraction of diaphragm is more efficient.
  • Innervation: Anterior rami of T12 – L4 nerves.
  • Blood supply: Lumbar, median sacral, iliolumbar and subcostal arteries.

Fig 1
The quadratus lumborum of the posterior abdominal wall.

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