====== Psoas major muscle ======

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The psoas major (/ˈsoʊ.əs/ or /ˈsoʊ.æs/,The word psoas comes from the Greek psoa meaning the “loin region.”) is a long fusiform muscle located on the side of the lumbar region of the vertebral column and brim of the lesser pelvis. It joins the iliacus muscle to form the iliopsoas.

The [[psoas muscle]] is the largest muscle at the cross section of the lower levels of lumbar spine
((Kim WH, Lee SH, Lee DY. Changes in the cross-sectional area of multifidus and 
psoas in unilateral sciatica caused by lumbar disc herniation. J Korean Neurosurg
Soc. 2011 Sep;50(3):201-4. doi: 10.3340/jkns.2011.50.3.201. Epub 2011 Sep 30.
PubMed PMID: 22102949; PubMed Central PMCID: PMC3218178.
)).

It stabilize the spine through its potential to generate large compressive forces, thereby increasing the spinal stiffness
((Barker KL, Shamley DR, Jackson D. Changes in the cross-sectional area of
multifidus and psoas in patients with unilateral back pain: the relationship to
pain and disability. Spine (Phila Pa 1976). 2004 Nov 15;29(22):E515-9. PubMed
PMID: 15543053.
)).

Unilateral disc herniation affects the psoas muscle at two locations (the lumbar spine and the hip joint) leading to more pronounced atrophy of the muscle compared with atrophy in other muscles
((Dangaria TR, Naesh O. Changes in cross-sectional area of psoas major muscle in
unilateral sciatica caused by disc herniation. Spine (Phila Pa 1976). 1998 Apr
15;23(8):928-31. PubMed PMID: 9580961.
)).