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The psoas major is a long fusiform muscle located 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.
The psoas major is divided into a superficial and deep part.
The deep part originates from the transverse processes of lumbar vertebrae 1-5.
The superficial part originates from the lateral surfaces of the last thoracic vertebra, lumbar vertebrae I1-4?and from neighboring intervertebral discs.
The lumbar plexus lies between the two layers of the muscle.
The iliacus and psoas major form the iliopsoas, which runs across the iliopubic eminence through the muscular lacuna to its insertion on the lesser trochanter of the femur.
The iliopectineal bursa separates the tendon of the iliopsoas muscle from the external surface of the hip joint capsule at the level of the iliopubic eminence.
The iliac subtendinous bursa lies between the lesser trochanter and the attachment of the iliopsoas.
Innervation of the psoas major is through the anterior rami of L1 to L3 nerves.
In less than 50 percent of patients the psoas major is accompanied by the psoas minor.
The psoas major joins the upper body and the lower body.
The psoas major joins the axial to the appendicular skeleton
As part of the iliopsoas, it contributes to flexion in the hip joint.
On the lumbar spine, unilateral contraction bends the trunk laterally, while bilateral contraction raises the trunk from its supine position.
It is part of a group of muscles called the hip flexors.
The hip flexors 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.
When doing a sit-up the hip flexors, including the iliopsoas, will flex the spine upon the pelvis.
Because of its frontal attachment on the vertebrae, rotation of the spine will stretch the psoas.
Tightness of the psoas can result in spasms or lower back pain by compressing the lumbar discs.
An inflamed psoas can lead to irritation and entrapment of the iliolinguinal and the iliohypogastric nerves, resulting in a sensation of heat or water running down the front of the thigh.
Psoas can be palpated with active flexion of the hip, and the appearance of a protruding belly can visually indicate a hypertonic psoas, which pulls the spine forward while pushing the abdominal contents outward.
Autopsy data show this muscle is thicker in those of African descent than in Caucasians, and that the presence of
The psoas minor is also racially variant, and she s thicker in those of African descent.