The iliopsoas muscle belongs to the inner hip muscles. It is actually built out of the two muscles, psoas major and iliacus muscles, which are separated in the abdomen, but later merge and share the same insertion in the thigh.
Psoas major: Vertebral bodies of T12- L4, Intervertebral discs between T12-L4, Costal processes of L1-L5 vertebrae
Iliacus: iliac fossa
|Insertions||Lesser trochanter of femur|
|Innervation||Femoral nerve (L2-L4) (Iliacus), Anterior rami of sacral plexus (L1-L3) (Psoas major)|
Iliacus- Hip joint: Thigh flexion
Psoas major- Hip joint: Thigh/trunk flexion, Thigh external rotation; Trunk lateral flexion
All of the important anatomical facts about the iliopsoas muscle will be described in this article.
The iliopsoas 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 bodies of the vertebrae T12-L4, the intervertebral discs between T12-L4, and the costal processes of the vertebrae L1-L5. (The muscle inserts at the lesser trochanter of the femur, as the iliopsoas muscle).
- Iliacus muscle - runs from the iliac fossa to the lesser trochanter.
Relations & Location
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 over 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).