Psoas major

The psoas major is a long, spindle-shaped muscle on each side of the lumbar spine. At its lower end it joins the iliacus to form the iliopsoas. (StatPearls, Psoas Major)

Latin musculus psoas major (Wikipedia, Psoas major muscle, CC BY-SA 4.0) · FMA18060 · Muscular system

The muscles of both lower limbs seen from the front, faded, with the right psoas major highlighted and labeled, running down from the lumbar region past the pelvis to the top of the right thigh. — The right psoas major in place, seen from the front. Render: ScienceQuest, CC BY 4.0. Meshes: BodyParts3D, © The Database Center for Life Science, CC BY 4.0

The right psoas major alone, seen from the front: a long, spindle-shaped muscle running down and slightly outward, tapering to its tendon at the bottom. — The right psoas major on its own, from the front. Render: ScienceQuest, CC BY 4.0. Meshes: BodyParts3D, © The Database Center for Life Science, CC BY 4.0

Open it in the Lower Limb Muscles Explorer See it alone in 3D

Where is the psoas major?

It arises from the transverse processes and the sides of the bodies of the first four lumbar vertebrae and the last thoracic vertebra, and from the discs between them. (StatPearls, Iliopsoas Muscle)

Its bundles run down beside the lumbar spine to the iliac fossa and merge with the iliacus. The two pass under the inguinal ligament and insert by one strong tendon on the lesser trochanter of the femur. (StatPearls, Iliopsoas Muscle)

The lumbar plexus lies between its deep and superficial layers. (StatPearls, Psoas Major)

What does the psoas major do?

With the iliacus it flexes the hip. Contracting on one side it helps bend the trunk sideways, and both sides together help lift the trunk when you are lying on your back. (StatPearls, Psoas Major)

It steadies the lumbar spine when you sit, and it holds the head of the femur in the acetabulum through the first 15° of hip movement. (StatPearls, Iliopsoas Muscle)

In walking it switches on as hip flexion begins and again late in the swing phase. (StatPearls, Psoas Major)

What lies around the psoas major?

It lies behind the kidney and the renal vessels, the ureter and the gonadal vessels, and behind the ascending colon on the right and the descending colon on the left. (StatPearls, Psoas Major)

Its inner edge meets the inferior vena cava on the right and the aorta on the left. (StatPearls, Psoas Major)

Branches of the lumbar plexus come out of its front and both borders: the genitofemoral nerve from its front, the obturator nerve from its inner border and the femoral nerve from its outer border. (StatPearls, Psoas Major)

Where the sources differ

Sources give three versions of its nerve supply: short branches of the lumbar plexus from L1 to L3, the anterior rami of L1 to L4 with small branches from the femoral nerve, or the ventral rami of L2 to L4. (StatPearls, Anterior Thigh Muscles, Psoas Major and Thigh Femoral Nerve)

The StatPearls iliopsoas article takes its origin from the last thoracic and first four lumbar vertebrae, and its psoas major article says classical textbooks such as Testut describe it the same way. The StatPearls thigh muscles article runs it from the lower border of T12 to L5. (StatPearls, Iliopsoas Muscle, Psoas Major and Thigh Muscles)

Sources agree that it rotates the femur laterally but differ on abduction and adduction. The StatPearls psoas major article says in one passage that its contraction abducts the femur, and in its function section that it adducts the femur. The iliopsoas article says the unit adducts it. (StatPearls, Psoas Major and Iliopsoas Muscle)

Psoas major at a glance
Feature	Detail and source
Origin	Transverse processes and bodies of the last thoracic and first four lumbar vertebrae, and the discs between them (StatPearls, Iliopsoas Muscle)
Insertion	Lesser trochanter of the femur, by a tendon shared with the iliacus (StatPearls, Iliopsoas Muscle)
Action	Flexes the hip; bends the trunk to its side; steadies the lumbar spine in sitting (StatPearls, Psoas Major and Iliopsoas Muscle)
Nerve	Branches of the lumbar plexus; the root levels differ between sources (StatPearls, Anterior Thigh Muscles and Psoas Major)

Touches in this model

Measured on the BodyParts3D meshes: surfaces within 2 mm of the psoas major, nearest first, 12 of 32.

Right adductor magnus in contact
Right iliacus in contact
Right pectineus in contact
Right quadratus femoris in contact
Diaphragm in contact
Fifth lumbar vertebra in contact
First lumbar vertebra in contact
Fourth lumbar vertebra in contact
Intervertebral disk of first lumbar vertebra in contact
Intervertebral disk of fourth lumbar vertebra in contact
Intervertebral disk of second lumbar vertebra in contact
Intervertebral disk of third lumbar vertebra in contact

Sources

StatPearls, Anatomy, Bony Pelvis and Lower Limb: Psoas Major. Marco A. Siccardi; Muhammad Ali Tariq; Cristina Valle. Last update August 8, 2023. CC BY-NC-ND 4.0. Read 2026-10-25.
StatPearls, Anatomy, Bony Pelvis and Lower Limb: Iliopsoas Muscle. Bruno Bordoni; Matthew A. Varacallo. Last update June 8, 2026. CC BY-NC-ND 4.0. Read 2026-10-25.
StatPearls, Anatomy, Bony Pelvis and Lower Limb: Anterior Thigh Muscles. Ayesha Khan; Abdul Arain. Last update March 17, 2023. CC BY-NC-ND 4.0. Read 2026-10-25.
StatPearls, Anatomy, Bony Pelvis and Lower Limb: Thigh Femoral Nerve. Nader A. Refai; Asa C. Black; Prasanna Tadi. Last update August 22, 2023. CC BY-NC-ND 4.0. Read 2026-10-25.
StatPearls, Anatomy, Bony Pelvis and Lower Limb: Thigh Muscles. Basem Attum; Matthew A. Varacallo. Last update December 17, 2022. CC BY-NC-ND 4.0. Read 2026-10-25.