Quadratus Lumborum

Abdomen · Trunk

The Quadratus Lumborum is found among the Abdomen muscles of the Trunk. It arises from Iliac crest and iliolumbar ligament and attaches to 12th rib and transverse processes of L1–L4. It is responsible for several movements: Lateral flexion of vertebral column; depresses and fixes 12th rib; bilateral extension. Its nerve supply is the Anterior rami of T12–L4.

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)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Quadratus Lumborum, work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.

Most students remember the Quadratus Lumborum fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.