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Psoas major

Origin, insertion, innervation and functions of the psoas major muscle.

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Hello again everyone! This is Matt from Kenhub, and in this tutorial, we will talk about the psoas major muscle, its origin, insertion, innervation and function.

The psoas major muscle is part of a team of two muscles that compose the iliopsoas muscle. The iliopsoas muscle belongs to the inner hip muscles and is made up of the psoas major and the iliacus muscles.

The psoas major muscle originates from the first to fourth lumbar vertebrae, the costal processes of all lumbar vertebrae and the twelfth thoracic vertebra, and inserts at the lesser trochanter of the femur.

The psoas major and iliacus muscle unify in the lateral pelvis shortly before the inguinal ligament becoming the iliopsoas muscle. There, they pass below the inguinal ligament through the muscular lacuna together with the femoral nerve. Both muscles are completely surrounded by the iliac fascia.

The innervation of the psoas major is carried by the direct branches of the lumbar plexus. The lumbar plexus lies dorsally from the psoas major muscle which is penetrated by the genitofemoral nerve. Medially from the psoas major runs the sympathetic trunk.

The iliopsoas muscle is the strongest flexor of the hip joint, a function which is important for walking. In the supine position, it decisively supports the straightening of the upper body, for example, during sit-ups. Furthermore, it rotates the thigh laterally. A unilateral contraction leads to a lateral flexion of the lumbar vertebrae column. Altogether, the iliopsoas muscle plays a significant role in the movement and stabilization of the pelvis.

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