Quadratus lumborum
Musculus quadratus lumborum
Also known as: QL, hip hiker
A quadrilateral muscle of the posterior abdominal wall between the 12th rib and the iliac crest. It laterally flexes the trunk, "hikes" the hip and fixes the 12th rib during inspiration.
Overview
Quadratus lumborum arises from the iliolumbar ligament and the internal lip of the posterior iliac crest. It ascends to the medial half of the inferior border of the 12th rib and the tips of the transverse processes of L1–L4. It lies lateral to psoas major and is enclosed between the anterior and middle layers of the thoracolumbar fascia. The lateral arcuate ligament of the diaphragm arches over its upper part.
Acting on one side, it laterally flexes the trunk to the same side or, with the trunk fixed, elevates (hikes) the hip on that side, as in walking with a stiff knee. Acting together, the two muscles extend the lumbar spine and stabilise it. During inspiration it fixes the 12th rib, giving the diaphragm a stable attachment. The subcostal, iliohypogastric and ilioinguinal nerves cross its anterior surface, and the kidney lies on it.
- Location
Posterior abdominal wall, lateral to the lumbar vertebrae.
Anatomy
- Origin
Iliolumbar ligament and the internal lip of the iliac crest.
- Insertion
Medial half of the inferior border of the 12th rib and the tips of the transverse processes of L1–L4.
- Action
Lateral flexion of the trunk; elevation of the hip; fixes the 12th rib; extension of the lumbar spine (bilaterally).
- Innervation
Anterior rami of T12 (subcostal nerve) and L1–L4.
- Nerve roots
T12–L4
- Arterial supply
Lumbar arteries, subcostal artery, iliolumbar artery (lumbar branch) and median sacral artery.
- Relations
Posterior to the kidney, colon, subcostal, iliohypogastric and ilioinguinal nerves; lateral to psoas major. Covered posteriorly by the middle layer of the thoracolumbar fascia and erector spinae.
Function
- Laterally flexes the lumbar spine
- Elevates the ilium (hip hiking)
- Fixes the 12th rib in inspiration
- Extends and stabilises the lumbar spine (bilaterally)
Clinical significance
Quadratus lumborum block
Regional anaesthesia around QL within the thoracolumbar fascia provides analgesia for abdominal and hip surgery.
Low back and referred pain
QL spasm or trigger points are a common source of unilateral low back pain that may refer to the buttock and the greater trochanter.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.