The psoas major muscle is a skeletal muscle of the hip musculature, also known as the great lumbar flexor. The hip muscle is involved in flexion and internal and external rotation in the hip joint and plays a role in the lateral flexion and inclination of the lumbar spine. Damage to the femoral nerve paralyzes the psoas major muscle.

What is the psoas major muscle?

The hip muscles are a group of skeletal muscles around the hip joint. The hip muscles encase the hip joint and attach to the proximal portion of the femur approach. Topographically and functionally, the hip muscles are divided into an inner, an outer and a deep portion.

The psoas major muscle corresponds to a skeletal muscle of the internal hip muscles. Together with the iliacus muscle, the hip muscle forms the functional unit of the iliopsoas muscle, which lies in the retroperitoneal space. The psoas major muscle can be subdivided into a superficial and a deeper layer, which have different origins. The superficial layer originates from the twelfth thoracic vertebrae, the first lumbar vertebrae and the intervertebral discs assigned to them. The deep layer has its origin in the transverse processes of the lumbar vertebrae. In the German specialist literature, the psoas major muscle is also referred to as the large lumbar muscle.

Anatomy & Construction

The psoas major muscle is in close proximity to the lumbar plexus. The motor innervation of the hip muscle takes over the direct branches of L1 to L4 of the lumbar plexus of the femoral nerve. The psoas major muscle takes its approach together with the iliac muscle on the trochanter minor of the femur (femur).

The superficial part and the deep part of the great lumbar muscle unite in the course of the iliac muscle. Together, the muscles are enveloped by fascia and referred to in this unit as the lumbar iliac muscle. The lumbar tendon muscle passes through the so-called muscle portal (Lacuna musculorum), where it reaches the small trochanter minor of the femur. The psoas major muscle usually contains the psoas minor muscle. In the human body, this muscle is extremely variable and is sometimes replaced by fascia. One of the important features of the psoas major muscle is the visibility of the tissue on X-ray images. Signals from the central nervous system reach the psoas major muscle via its motor end plate.

Function & Tasks

The psoas major muscle is a muscle close to the joints. Joints correspond to movable bone connections and allow different types of movement depending on their anatomical position. These movements are performed by joint-near muscles, which have their attachment to one of the clashing bones. The approach of the psoas major muscle proximal part of the femur, which hits the pelvic bone in the hip joint. The hip joint is a nut joint.

In the acetabulum of the joint is the femoral head, which corresponds to an approximately spherical extension of the femur. Because the great lumbar flexor is in direct connection with the femur, its contraction moves the femoral head in the hip joint. Depending on the initial position, all muscles of the hip muscles move the hip when the pelvis is fixed or the pelvis when the thigh is fixed. The contractions of the hip muscles thus enable everyday forms of movement such as standing and walking. Together with the iliacus muscle, the psoas major muscle forms the iliopsoas muscle, which is regarded as the strongest flexor of the hip joint. The diffraction is also referred to in the jargon as flexion. The extension or extension in the hip joint is the opposite form of movement that is initiated by the extensors of the hip muscles.

The functional unit of psoas major muscle and iliacus muscle is responsible not only for the flexion in the hip joint, but also for the erection of the trunk area from the supine position. This erection requires namely a flexion in the hip joint. In addition, the two muscles roll the thigh outward and are thus involved in the rotational movement in the joint. The psoas major muscle also participates in the lateral tilt (lateral flexion) and the inclination of the lumbar spine.


Paralysis of the psoas major muscle occurs as part of damage to the supplying femoral nerve. This peripheral nerve supplies a variety of muscles. The femoral nerve paralysis is expressed in the form of severe movement disorders. Complete paresis of the nerve structure leads to total failure of the psoas group.

The hip joint can not be actively bent anymore. In addition, those affected can not or hardly get up from lying down. In addition, the patient's knee remains flexed and can not be stretched on its own. When it occurs, the affected person bends his leg. In the reflex examination, the neurologist notices a loss or weakening of the patellar tendon reflex. Femoral palsy can be caused, for example, by hematomas, especially bruising in the iliacus muscle and psoas muscle. Postoperatively, the nerve may become paralyzed due to stretching or pressure damage in the appendix area as well as through prostatectomies, kidney transplants, deliveries or more severe hip surgery.

Traumatic paralysis of the nerve is usually based on an uncontrolled and sudden hyperextension. In individual cases, tumors or aneurysms compress the nerve structure, which can also lead to paralysis of the psoas major muscle. Also compression by hyperplastic thighbones are conceivable. In individual cases, paralysis also occurs after a herpes simplex infection. The right large lumbar muscle may also indicate inflammation of the appendix. Inflammation of the appendix causes pain in the right lower abdominal region in the event of a severe contraction of the muscle as a result of thigh flexion.

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