Muscle
Psoas major
Spine-to-femur muscle contributing to hip flexion
High-yield
Its main supply comes from direct lumbar anterior-ramus branches, commonly taught as L1-L3. Additional L4 and femoral branches have been described, so it is better distinguished from iliacus by its main pattern than by an absolute exclusion.
Overview
Psoas major descends beside the lumbar spine, crosses the pelvic brim and reaches the lesser trochanter with iliacus. Its attachments let it act across the hip while also contributing to control of the trunk and lumbar region.
Reference facts
- Origin
- Lumbar transverse processes, sides of T12-L5 vertebral bodies and intervening discs; the exact attachment extent varies
- Insertion
- Lesser trochanter through the iliopsoas tendon, shared with iliacus
- Action
- Flexes the hip; with the lower limb fixed, contributes to trunk flexion and lumbar control
- Innervation
- Mainly direct anterior rami of upper lumbar nerves, usually summarized as L1-L3; L4 and femoral contributions are documented
- Blood supply
- Lumbar and iliolumbar branches, with contributions from neighboring iliac, obturator and femoral vessels
Clinical correlation
Inflammation next to psoas can make hip movement painful, as in some cases of retrocecal appendicitis. The psoas sign is a clinical clue: its presence does not establish appendicitis, and its absence does not exclude it.
Frequently asked questions
What does the psoas major do?
Flexes the hip; with the lower limb fixed, contributes to trunk flexion and lumbar control.
What nerve innervates the psoas major?
Mainly direct anterior rami of upper lumbar nerves, usually summarized as L1-L3; L4 and femoral contributions are documented.
Where does the psoas major attach?
Origin: Lumbar transverse processes, sides of T12-L5 vertebral bodies and intervening discs; the exact attachment extent varies. Insertion: Lesser trochanter through the iliopsoas tendon, shared with iliacus.
What is the blood supply of the psoas major?
The psoas major is supplied by the lumbar and iliolumbar branches, with contributions from neighboring iliac, obturator and femoral vessels.