|Origin||Inner lip of iliac crest
Transverse processes vertebra L1-L4
|Action||Can assist with inspiration by bracing the twelfth rib
Can assist in stabilization of spine and pelvis
Bilateral contraction: Assists with extension of the trunk
Unilateral contraction: Assists with lateral flexion of the trunk
|Nerve||12th thoracic intercostal nerve
A lumbar branch of the iliolumbar artery
Location & Overview
The quadratus lumborum muscle is located towards the posterior of the body and deep to the lower back musculature. It is a deep muscle and is classed as a muscle of the posterior abdominal wall and located dorsally to the iliopsoas muscle. It is located laterally either side of the spine. Its shape can sometimes be irregular. However, generally it is quadrangular shaped, hence the Latin ‘quadratus’ lumborum  .
Origin & Insertion
The quadratus lumborum muscle originates on the inner lip of the iliac crest and iliolumbar ligament. It then inserts onto the internal surface and inferior border of the 12th rib and the transverse processes of vertebra L1 to L4 .
When both sides of the quadratus lumborum contract (bilateral contraction), this assists in extension of the trunk. When just one side contracts (unilateral contraction) this assists in lateral flexion of the trunk . The quadratus lumborum can also assist with inspiration (breathing in). It is thought the quadratus lumborum is primarily designed as a respiratory muscle by bracing or anchoring the 12th rib allowing for a stable base for the diaphragm .
In terms of the quadratus lumborum’s ability to extend and laterally flex the trunk, the forces it produces are comparatively weak compared to other muscles, such as the erector spinae. For example, the quadrates lumborum is only able to exert at best 10% of the force the erector spinae produces during these movements  . Even the compression forces produced by the quadratus lumborum are comparatively weak compared to the erector spinae and multifidus muscles. Therefore, it does not play a significant role in stabilization of the lumbar spine either, though it can contribute somewhat. This is thought to be because of the comparatively small size and limited number of muscle fascicles compared to the erector spinae and multifidus .
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Quadratus Lumborum Flashcards
|↑1, ↑3, ↑4, ↑7, ↑10, ↑12||Bordoni B, Varacallo M. Anatomy, Abdomen and Pelvis, Quadratus Lumborum. [Updated 2022 Jul 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535407/|
|↑2||Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017|
|↑5, ↑6, ↑8||Phillips S, Mercer S, Bogduk N. Anatomy and biomechanics of quadratus lumborum. Proc Inst Mech Eng H. 2008 Feb;222(2):151-9. doi: 10.1243/09544119JEIM266. PMID: 18441751.|
|↑9||Grzonkowska M, Baumgart M, Badura M, Dombek M, Wiśniewski M, Paruszewska-Achtel M, Szpinda M. Quantitative anatomy of the growing quadratus lumborum in the human foetus. Surg Radiol Anat. 2018 Jan;40(1):91-98. doi: 10.1007/s00276-017-1901-4. Epub 2017 Jul 29. PMID: 28756538; PMCID: PMC5820394.|
|↑11||Beveridge TS, Power A, Johnson M, Power NE, Allman BL. The lumbar arteries and veins: Quantification of variable anatomical positioning with application to retroperitoneal surgery. Clin Anat. 2015 Jul;28(5):649-60. doi: 10.1002/ca.22504. Epub 2015 Feb 2. PMID: 25644404|