Anatomy and supply
The iliopsoas muscle belongs to the inner hip muscles. It comprises a complex of two muscles with different areas of origin. This muscle belongs to the striated musculature and the innervation is carried by the femoral nerve as well as direct branches of the lumbar plexus. The iliopsoas muscle consists of:
- Psoas major muscle: originates from the 1st to 4th lumbar vertebrae, the costal processes of all lumbar vertebrae and the 12th thoracic vertebrae and inserts at the lesser trochanter of the femur.
- Iliacus muscle: runs from the iliac fossa to the lesser trochanter.
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 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 (important walking muscle). In the supine position it decisively supports the straightening of the upper body (e.g. 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.
Abrupt movements (e.g. shooting the soccer ball) and overload may cause an inflammation of the tendon or the associated bursa (iliopsoas syndrome). A pathological shortening of the muscle leads to hyperlordosis of the lumbar vertebrae column on the long term due to unnatural and incorrect strain. In rare cases an abscess (e.g. in bacterial spondylodiscitis) can spread within the iliac fascia and the muscle compartment until it reaches the lesser trochanter (psoas abscess).