Psoas major muscle

Psoas major muscle
The psoas major and nearby muscles
Horizontal disposition of the peritoneum in the lower part of the abdomen. (Psoas major labeled at bottom left.)
Latin	m. psoas major
Gray's	subject #127 467
Origin	Transverse processes of T12-L5 and the lateral aspects of the discs between them
Insertion	in the lesser trochanter of the femur
Artery	lumbar branch of iliolumbar artery
Nerve	Lumbar plexus via anterior branches of L2-L4 nerves
Actions	flexes and rotates laterally thigh
Antagonist	Gluteus maximus
MeSH	Psoas+Muscles

The psoas major is a long fusiform muscle placed on the side of the lumbar region of the vertebral column and brim of the lesser pelvis. It joins the iliacus muscle to form the iliopsoas. In less than 50 percent of subjects^[1] the psoas major is accompanied by the psoas minor.

Location

Origin

The psoas major is divided into a superficial and deep part. The deep part originates from the costal processes of lumbar vertebrae I-V. The superficial part originates from the lateral surfaces of the last thoracic vertebra, lumbar vertebrae I-IV, and from neighbouring invertebral discs. The lumbar plexus lies between the two layers. ^[1]

Insertion

Joined by the iliacus, psoas major forms the iliopsoas which is surrounded by the iliac fascia. The iliopsoas runs across the iliopubic eminence through the muscular lacuna to its insertion on the lesser trochanter of the femur. The iliopectineal bursa separates the bone from the muscle at the level of the iliopubic eminence. The iliac subtendinous bursa lies between the lesser trochanter and the attachment of the iliopsoas. ^[1]

Innervation

Innervation of the psoas major is through the anterior rami of L2 to L4

Function

As part of the iliopsoas, psoas major contributes to flexion and external rotation in the hip joint. On the lumbar spine, unilateral contraction bends the trunk laterally, while bilateral contraction raises the trunk from its supine position. ^[2]

It forms part of a group of muscles called the hip flexors, whose action is primarily to lift the upper leg towards the body when the body is fixed or to pull the body towards the leg when the leg is fixed.

For example, when doing a situp that brings the torso (including the lower back) away from the ground and towards the front of the leg, the hip flexors (including the iliopsoas) will flex the spine upon the pelvis.

See also

• Iliopsoas
• Iliacus
• Hip flexor
• Psoas minor muscle
• Iliopsoas tendinitis

Notes

References

• Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. ISBN 3-13-533305-1. 
• Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme. 2006. ISBN 1-58890-419-9. 

Additional images

Right femur. Anterior surface.	Diagram of a transverse section of the posterior abdominal wall, to show the disposition of the lumbodorsal fascia.	The diaphragm. Under surface.	Muscles of the iliac and anterior femoral regions.
The arteries of the pelvis.	The relations of the femoral and abdominal inguinal rings, seen from within the abdomen. Right side.	The thoracic and right lymphatic ducts.	The lumbar plexus and its branches.
Nerves of the right lower extremity. Front view.	Sacral plexus of the right side.	Transverse section, showing the relations of the capsule of the kidney.

External links

• -1261436848 at GPnotebook
• LUC psmj
• SUNY Labs 40:16-0101 - "Posterior Abdominal Wall: Muscles of the Posterior Abdominal Wall"
• SUNY Anatomy Image 8916
• Cross section at UV pelvis/pelvis-e12-2
• Psoas Stretches for Back Pain
• Psoas Muscles and Abdominal Exercises for Back Pain

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated.