Psoas major originates along the entire lumbar spine, making it unique in spanning from thoracolumbar junction to the lesser trochanter. Its compressive force on the lumbar spine during sit-ups is clinically significant.
| Origin | Lateral surfaces of T12-L5 vertebral bodies and intervertebral discs; Transverse processes of L1-L5 |
|---|---|
| Insertion | Lesser trochanter of the femur — combined with iliacus as the iliopsoas tendon |
| Nerve Supply | Direct ventral rami of L1, L2, L3 |
| Blood Supply | Lumbar arteries and iliolumbar artery |
| Actions | Flexes the hip — the primary contributor to the iliopsoas; Flexes and laterally flexes the lumbar spine when acting from the femur; Compresses the lumbar vertebral bodies when acting bilaterally |
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Psoas abscess (from vertebral osteomyelitis or Crohn's disease) tracks along the psoas sheath to present as a fluctuant inguinal mass or hip pain. Psoas haematoma in anticoagulated patients compresses the femoral nerve producing thigh weakness and sensory loss. Psoas release in hip flexion contracture surgery lengthens the musculotendinous unit at multiple levels.
Palpated in the iliac fossa with deep pressure, and the tendon at the medial inguinal region during resisted hip flexion.
Anticoagulation-related bleeding into the psoas sheath compressing the femoral nerve, producing quadriceps weakness and anterior thigh sensory loss, managed by anticoagulation reversal and haematoma drainage.
