Posterior abdominal wall

Anatomy · Abdomen & pelvis anatomy

Muscle	Innervation & Action
Psoas Major	Innervation: Lumbar Plexus anterior rami L1-L4 Action: Flexion and medial rotation of femur
Quadratus Lumborum	Innervation: T12-L4 spinal nerves Action: Lateral flexion of vertebral column
Iliacus	Innervation: Femoral nerve Action: Flexion and medial rotation of thigh

Note iliacus and psoas are sometimes referred to together as iliopsoas as they have the same insertion onto the lesser trochanter and the same action on the femur.

Also note that the direction of rotation is controversial. Many texts say psoas and iliacus are lateral rotators. Some studies say flexion is usually in the neutral line (i.e. without rotation). The RCEM however considers the iliopsoas muscle group to be medial rotators and as they are marking the exam we will go with them.

Diagram illustrating iliacus and psoas major

Anterior view illustrating relations of quadratus lumborum

Anterior view illustrating relations of quadratus lumborum

Diagram illustrating relations of quadratus lumborum on cross section. Note the lateral position of transversus abdominus and medial relation of psoas major