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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
Action	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.

Location

Origin

It arises:

• (1) from the anterior surfaces of the bases and lower borders of the transverse processes of all the lumbar vertebrae
• (2) from the sides of the bodies and the corresponding intervertebral fibrocartilages of the last thoracic and all the lumbar vertebrae by five slips, each of which is attached to the adjacent upper and lower margins of two vertebrae, and to the intervertebral fibrocartilage;
• (3) from a series of tendinous arches which extend across the constricted parts of the bodies of the lumbar vertebrae between the previous slips; the lumbar arteries and veins, and filaments from the sympathetic trunk pass beneath these tendinous arches.

Insertion

The muscle proceeds downward across the brim of the lesser pelvis, and diminishing gradually in size, passes beneath the inguinal ligament and in front of the capsule of the hip-joint and ends in a tendon; the tendon receives nearly the whole of the fibers of the Iliacus and is inserted into the lesser trochanter of the femur.

A large bursa which may communicate with the cavity of the hip-joint, separates the tendon from the pubis and the capsule of the joint.

Function

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 sit up 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.

Indications

Crepitus, or “popping” in the lower back can indicate unequal lateral forces on the lumbar spine owing to a strength and/or laxity discrepancy between the right and left psoas major muscles.¹ Tight hip flexors (psoas, illiacus, tensor fascia latae), either unilaterally or bilaterally (one side or both sides), are a common though unsung cause of lower back pain, and can be accompanied by Iliopsoas tendinitis, or “snapping hip syndrome.” Physical therapists may recommend stretching and/or strengthening of one of both psoas muscles if lower back pain is indicated.

Stretching the psoas can be difficult because it is impossible to isolate the muscle, and thus any stretch thereof must necessarily stretch all hip flexor muscles and typically the quadriceps as well. Strengthening the psoas is also tricky, but typically involves some variation of supine leg raises, or, in a gym setting, knee raises on a levered machine. A common evaluation of psoas strength is to ask the patient to stand straight up with back against a wall, feet 2-3 inches from the wall. The patient is then instructed to raise the knee as high (close to the chest as possible) for 30 seconds. If the patient’s knee falls below horizontal (femur below 90 degrees) before 30 seconds has elapsed, weakness of the iliopsoas on the side of the knee being raised is indicated.

See also

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

References

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. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.