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Quadratus lumborum muscle - want to learn more about it?

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Quadratus lumborum muscle

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.

Key Facts
Origin Transverse process of L5 vertebra, iliac crest, iliolumbar ligament
Insertion Transverse processes of L1-L5 vertebrae, inferior border of 12th rib
Innervation Anterior rami of T12-L4 spinal nerves
Function

Depression and stabilization of 12th rib

Lateral flexion of trunk

Clinical Chornic pain in lower back

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

Anatomy

Origins & Insertions

It starts from the iliac crest of the ilium and runs craniomedially, attaching to the 12th rib and the transverse processes of the 1st to 5th lumbar vertebrae. All fibers together give the muscle a rectangular appearance.

Innervation

The innervation is supplied by the subcostal nerve and branches of the lumbar plexus.

Relations

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.

Function

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).

Clinical Aspects

Overuse and strain of the quadratus lumborum are one of the major causes for chronic pain in the lower back. One typical cause is the habit of sitting at the desk using a reclined seat, which releases the intrinsic back muscles and weakens them in the long term. The weak back muscles must now be compensated by the quadratus lumborum leading to painful tension and stiffening of the muscle.

Other causes can be direct damage or any type of imbalance of the pelvis or spine which forces the quadratus lumborum to stabilize them. An example of that type of imbalance is unequal leg lengths.

Quadratus lumborum muscle - want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

Sign up for your free Kenhub account today and join over 1,104,786 successful anatomy students.

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Show references

References:

  • D. Drenckhahn/J. Waschke: Taschenbuch Anatomie, 1st edition, Urban & Fischer Verlag/Elsevier (2008), p. 145
  • M. Schünke/E. Schulte/U. Schumacher: Prometheus – LernAtlas der Anatomie – Allgemeine Anatomie und Bewegungssystem, 2nd edition, Thieme Verlag (2007), p. 152 G.
  • Fors: Why we hurt – a complete physical and spiritual guide to healing your chronic pain, Llewellyn Publications (2007), p. 135-138

Author:

  • Achudhan Karunaharamoorthy

Illustrators:

  • Quadratus lumborum muscle - ventral view - Yousun Koh
  • Subcostal nerve - ventral view - Yousun Koh
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