Quadratus Lumborum
Abdomen · Trunk
The quadratus lumborum is a thick, roughly quadrilateral muscle of the posterior abdominal wall that lies deep in the lower back on either side of the lumbar spine. It arises from the iliac crest and iliolumbar ligament and ascends to insert on the 12th rib and the transverse processes of L1 to L4. Acting on one side it laterally flexes the vertebral column, bending the trunk to that side, and it also depresses and fixes the 12th rib, a role that steadies the rib against the upward pull of the diaphragm during breathing; acting on both sides it helps extend the lumbar spine. It is supplied by the anterior rami of T12 to L4. Because it hikes the hip when the pelvis is free to move, it is often described as a hip hitcher.
Origin, Insertion, Action & Nerve
Origin
Iliac crest and iliolumbar ligament
Insertion
12th rib and transverse processes of L1–L4
Action
Lateral flexion of vertebral column; depresses and fixes 12th rib; bilateral extension
Nerve
Anterior rami of T12–L4
Attachments explained
The Quadratus Lumborum is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Iliac crest and iliolumbar ligament
Insertion
12th rib and transverse processes of L1–L4
Action & function
When the Quadratus Lumborum contracts, it produces the following movements: Lateral flexion of vertebral column; depresses and fixes 12th rib; bilateral extension.
As part of the Abdomen group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Quadratus Lumborum receives its nerve supply from the Anterior rami of T12–L4. This nerve carries fibres from spinal segment(s) T12, L4.
Because a muscle can only contract when its nerve is intact, injury to the Anterior rami of T12–L4 or to its spinal roots (T12, L4) can weaken or paralyse the Quadratus Lumborum, impairing the movements it normally produces (lateral flexion of vertebral column). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Quadratus Lumborum (the OIANS method)
Learn quadratus lumborum by picturing a square slab bridging the iliac crest below to the 12th rib and lumbar transverse processes above. A one-sided pull shortens that side and bends the trunk laterally, while fixing the pelvis lets it hike the hip, so calling it the hip hitcher captures its most testable action.
Do not forget its respiratory role: by anchoring the 12th rib, it steadies the lower attachment of the diaphragm so that muscle can pull effectively during forceful breathing. Remembering its deep position on the posterior abdominal wall and its segmental supply from T12 to L4 keeps it distinct from the more superficial erector spinae behind it.
Frequently asked questions
Where is the Quadratus Lumborum located?
The Quadratus Lumborum is a muscle of the Abdomen group, located in the Trunk.
What is the origin of the Quadratus Lumborum?
Iliac crest and iliolumbar ligament
What is the insertion of the Quadratus Lumborum?
12th rib and transverse processes of L1–L4
What movements does the Quadratus Lumborum produce?
Lateral flexion of vertebral column; depresses and fixes 12th rib; bilateral extension
What nerve supplies the Quadratus Lumborum?
Anterior rami of T12–L4
Is the Quadratus Lumborum free to study in OIANS?
The Quadratus Lumborum is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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