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The iliopsoas (Latin: musculus iliopsoas) is a compound pelvic muscle composed of the psoas major and iliacus. Both muscles have different origin sites, but they share a common insertion place. The iliopsoas belongs to the anterior compartment of the pelvic muscles and is a muscle of the posterior abdominal wall. It is the strongest and main hip flexor muscle. Besides the thigh flexion, the iliopsoas also provides external rotation of the thigh at the hip joint.

The psoas major originates from the twelfth thoracic (Th12) and first four lumbar vertebrae (L1 - L4) and their corresponding intervertebral discs. In contrast, the iliacus originates from the iliac fossa. The psoas major and iliacus muscles merge at the level of the hip joint capsule, forming a common tendon for iliopsoas muscle. And finally, the iliopsoas muscle inserts on the lesser trochanter of the femur.