Expansion
Psoas major, iliacus, quadratus lumborum and transversus abdominis
Expansion
- Psoas major - from the lumbar transverse processes and vertebral bodies to the lesser trochanter; a hip flexor
- Psoas minor - present in only about 60 per cent of people
- Iliacus - from the iliac fossa, joining psoas as iliopsoas
- Quadratus lumborum - from the iliac crest to the twelfth rib and lumbar transverse processes
- Transversus abdominis - its aponeurotic posterior part
The lumbar plexus forms within psoas major. Its branches emerge in a characteristic pattern: the genitofemoral nerve on the anterior surface, the femoral nerve at the lateral border, and the obturator nerve at the medial border.
A psoas abscess, from tuberculosis, Crohn’s disease or a vertebral source, tracks down the muscle sheath to present as a groin swelling, with a flexed hip and a positive psoas stretch test.