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Quadratus lumborum muscle

Recommended video: Muscles of the trunk [21:21]
Main muscles of the thorax, abdomen and back.
Quadratus lumborum muscle (Musculus quadratus lumborum)

The quadratus lumborum muscle is a muscle of the posterior abdominal wall lying deep inside the abdomen and dorsal to the iliopsoas. It is the deepest muscle of the posterior abdominal wall, and it is often mistakenly referred to as one of the muscles of the back. Its shape is irregular, but is generally quadriangular, which is the reason why it is described as 'quadratus' in latin.

Besides the spine, it also attaches to the twelwth rib, which makes it very important for stabilization of both vertebral column and the rib during various movements of the spine. In order to palpate the muscle one needs place the fingers above the posterior iliac crest at the level of the hip.

This article will discuss the anatomy and clinical importance of the quadratus lumborum muscle.

Key facts about the quadratus lumborum muscle
Origin Iliac crest, iliolumbar ligament
Insertion Inferior border of rib 12, transverse processes of vertebrae L1-L4
Innervation Subcostal nerve (T12), anterior rami of spinal nerves L1-L4
Blood supply Lumbar, median sacral, iliolumbar and subcostal arteries
Function Bilateral contraction - fixes Ribs 12 during inspiration, trunk extension
Unilateral contraction - lateral flexion of trunk (ipsilateral)
  1. Origin and insertion
  2. Relations
  3. Innervation
  4. Blood supply
  5. Function
  6. Clinical aspects
  7. Sources
+ Show all

Origin and insertion

Quadratus lumborum originates from the iliolumbar ligament and iliac crest. It runs craniomedially, attaching to the inferior border of 12th rib and the transverse processes of the 1st to 4th lumbar vertebrae. All fibers together give the muscle a rectangular appearance.


The quadratus lumborum fills a great amount of space within the abdomen and is therefore in close proximity to many structures. The colon, the kidneys and the diaphragm are located ventrally to the muscle, whereas the intrinsic back muscles lie dorsomedially.

Both the iliohypogastric and ilioinguinal nerves course on the ventral surface of the quadratus lumborum after exiting the lumbar plexus and continue towards the lateral abdominal muscles.

Looking for a fast and effective way to consolidate your knowledge on the quadratus lumborum? With charts listing the attachments, innervations and functions of every muscle, our trunk wall muscle chart is an essential revision tool.


Quadratus lumborum is innervated by the subcostal nerve (T12) and anterior rami of spinal nerves L1-L4.

Blood supply

Blood supply to quadratus lumborum comes from the branches of lumbar, subcostal, median sacral, and iliolumbar arteries.


Essentially, the quadratus lumborum contributes to the stabilization and movement of the spine and the pelvis. A bilateral contraction leads to an extension of the lumbar vertebral column. When the muscle is only activated on one side, the trunk is bent towards that direction (lateral flexion).

In addition, the muscle fixes the 12th rib during movements of the thoracic cage and this way supports expiration (accessory muscle of expiration).

Learn everything about the muscles of the abdominal wall with our articles, video tutorials, quizzes and labeled diagrams.

...or if you're feeling ready to test your knowledge right away, try out our abdominal muscles quiz!

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