Quadratus lumborum muscle

Quadratus lumborum muscle
The left quadratus lumborum, one of the posterior abdominal muscles, is depicted in red.
Details
OriginPosterior border of iliac crest
InsertionInferior border of 12th rib and L1-L4
ArteryLumbar arteries, lumbar branch of iliolumbar artery
NerveThe twelfth thoracic and first through fourth ventral rami of lumbar nerves (T12, L1-L4)
ActionsAlone (unilateral), lateral flexion of vertebral column; Together (bilateral), depression of thoracic rib cage
Identifiers
Latinmusculus quadratus lumborum
TA98A04.5.01.027
TA22382
FMA15569
Anatomical terms of muscle

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.

  1. ^ Core Topics in Pain, p. 131, Anita Holdcraft and Sian Jaggar, 2005.