Quadratus lumborum muscle

Quadratus lumborum muscle
The left quadratus lumborum, one of the posterior abdominal muscles, is depicted in red.
Details
Origin	Posterior border of iliac crest
Insertion	Inferior border of 12th rib and L1-L4
Artery	Lumbar arteries, lumbar branch of iliolumbar artery
Nerve	The twelfth thoracic and first through fourth ventral rami of lumbar nerves (T12, L1-L4)
Actions	Alone (unilateral), lateral flexion of vertebral column; Together (bilateral), depression of thoracic rib cage
Identifiers
Latin	musculus quadratus lumborum
TA98	A04.5.01.027
TA2	2382
FMA	15569
Anatomical terms of muscle [edit on Wikidata]

The quadratus lumborum muscle, informally called the QL, is a paired muscle of the left and right posterior abdominal wall. It is the deepest abdominal muscle, and commonly referred to as a back muscle. Each muscle of the pair is an irregular quadrilateral in shape, hence the name.

The quadratus lumborum muscles originate from the wings of the ilium; their insertions are on the transverse processes of the upper four lumbar vertebrae plus the lower posterior border of the twelfth rib. Contraction of one of the pair of muscles causes lateral flexion of the lumbar spine, elevation of the pelvis, or both. Contraction of both causes extension of the lumbar spine.

A disorder of the quadratus lumborum muscles is pain due to muscle fatigue from constant contraction due to prolonged sitting, such as at a computer or in a car.^[1] Kyphosis and weak gluteal muscles can also contribute to the likelihood of quadratus lumborum pain.