Trunk (thorax, abdomen, back)

Quadratus Lumborum

Musculus quadratus lumborum

Origin

Iliac crest and iliolumbar ligament

Insertion

12th rib and transverse processes of L1-L4

Function

Lateral flexion of the trunk; fixes the 12th rib during deep inspiration and expiration (e.g. coughing)

Innervation

Branches of T12-L4 (subcostal nerve and lumbar plexus)

Movement & chain

Unilateral contraction produces ipsilateral lateral flexion; bilateral contraction stabilizes the pelvis and lumbar spine in the frontal plane, essential during single-leg standing (contralateral pelvic stabilization)

Palpation

Deeply located behind the lateral abdominal wall; indirectly accessible between the 12th rib and the iliac crest in side-lying, palpable during active lateral flexion against resistance

Clinical

Frequent source of unilateral low back pain and trigger points, often associated with a leg length discrepancy or prolonged asymmetric sitting

Segmental innervation

Myotome T12-L4.

In clinical practice

A regular target muscle for the 'quadratus lumborum block' (QL block), an ultrasound-guided nerve block for postoperative pain relief after abdominal and hip surgery.

Region in the model

Trunk (thorax, abdomen, back)