Psoas Major Detail

musculus psoas major detail

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.

Nerve: Direct ventral rami of L1, L2, L3 Blood Supply: Lumbar arteries and iliolumbar artery Region: Abdomen

Anatomical Data

Origin, Insertion & Supply

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

Biomechanics

Function & Actions

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

Clinical Relevance

Clinical Notes

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.

Palpation

Palpated in the iliac fossa with deep pressure, and the tendon at the medial inguinal region during resisted hip flexion.

Pathology

Common Injuries & Conditions

Psoas Haematoma with Femoral Nerve Compression

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.