A four-sided muscle between the last rib and the iliac crest, lying behind the kidney in the wall of the abdomen
Quadratus lumborum — the deep muscle of the loin.
Anatomy · Muscles
Quadratus lumborum
The deep muscle of the loin that hitches the hip
Posterior abdominal wall · lateral flexion of the trunk
A thick, four-sided muscle that fills the space between the last rib and the top of the hip bone on each side of the lumbar spine, forming part of the back wall of the abdomen. It bends the trunk sideways, hitches the pelvis up when one leg is lifted, and holds down the last rib so the diaphragm has a firm base to pull from. The kidney lies in front of it.
How to spot them
- ▸A quadrilateral sheet in the posterior abdominal wall between the iliac crest, the lumbar transverse processes and the twelfth rib
- ▸Lies lateral to psoas major and in front of the erector spinae, behind the kidney
- ▸The subcostal, iliohypogastric and ilioinguinal nerves run down in front of it
- ▸Supplied by the ventral rami of T12 to L4
What to know
When you lift one leg off the ground while walking, it hitches the pelvis up on that side
Quadratus lumborum — the hip hiker, lateral flexion of the trunk or pelvis.
It fixes the last rib during breathing in so that the diaphragm can pull effectively
Quadratus lumborum — it anchors the 12th rib.
Runs from the iliolumbar ligament and the iliac crest to the transverse processes of the upper four lumbar vertebrae
Quadratus lumborum — its attachments on the pelvis and the lumbar spine.
Three nerves of the abdominal wall, the subcostal, iliohypogastric and ilioinguinal, cross its front surface
Quadratus lumborum — these nerves lie on its anterior surface.
A deep regional anaesthetic block is placed on the front or side of it to numb the abdominal wall after lower abdominal surgery
Quadratus lumborum — the QL block.
Spasm or tightness of this muscle is a well-recognised source of deep, one-sided ache in the low back
Quadratus lumborum — a common source of mechanical low back pain.
Key ideas
- Acting on both sides together, it braces the lumbar spine from side to side and helps in extension; acting on one side with the erector spinae it bends the trunk sideways, and it is one of the main stabilisers in walking.
- The kidney and the perinephric fat lie on its anterior surface, and the psoas major overlies its medial edge, so a psoas abscess or a renal infection can produce pain in the same region.
Quick-fire facts
- •Origin: the iliac crest and the iliolumbar ligament
- •Insertion: the inferior border of the 12th rib and the transverse processes of L1 to L4
- •Action: lateral flexion of the vertebral column to the same side; extension when acting on both sides; fixes the 12th rib during inspiration
- •Nerve supply: the anterior rami of T12 to L4
- •Blood supply: the lumbar, iliolumbar, subcostal and median sacral arteries
- •It forms part of the posterior abdominal wall with the psoas major and iliacus
- •It lies between the anterior layer of the thoracolumbar fascia in front and the middle layer behind
- •The subcostal nerve and vessels, and the iliohypogastric and ilioinguinal nerves, lie in front of it
- •It is sometimes called the hip hiker for its role in lifting one side of the pelvis
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Sources
- TeachMeAnatomy — Quadratus lumborum