Human Anatomy
Posterior Abdominal Wall
Posterior abdominal wall for MBBS: psoas and quadratus lumborum, abdominal aorta and inferior vena cava, lumbar plexus and psoas abscess, mapped to NMC codes AN45.1 to AN45.3.
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Posterior Abdominal Wall
Posterior abdominal wall for MBBS: psoas and quadratus lumborum, abdominal aorta and inferior vena cava, lumbar plexus and psoas abscess, mapped to NMC codes AN45.1 to AN45.3.
The posterior abdominal wall chapter covers its muscles, the great vessels lying on the vertebral column, and the lumbar plexus formed within psoas major. It underpins the anatomy of psoas abscess, retroperitoneal surgery and the nerves of the lower limb.
High-yield: Posterior Abdominal Wall
- The muscles of the posterior abdominal wall are the psoas major, quadratus lumborum and iliacus.
- The psoas major and iliacus join to form iliopsoas, the main flexor of the hip.
- The abdominal aorta lies on the vertebral column and ends by dividing into the two common iliac arteries at the fourth lumbar vertebra.
- The inferior vena cava lies to the right of the aorta and is formed by the union of the common iliac veins.
- The lumbar plexus is formed within the psoas major from the ventral rami of the first four lumbar nerves.
- The femoral nerve emerges from the lateral border of psoas and the obturator nerve from its medial border.
- The genitofemoral nerve pierces the front of psoas and supplies the cremaster muscle and skin of the thigh.
- The kidneys lie on the posterior abdominal wall, with the right kidney slightly lower because of the liver.
- The sympathetic trunk runs along the sides of the lumbar vertebrae behind the great vessels.
- The cisterna chyli lies behind the aorta and is the dilated origin of the thoracic duct.
- The subcostal nerve and the lower intercostal nerves run on the posterior wall to reach the abdomen.
- A psoas abscess can track down along the muscle into the thigh, presenting as a swelling below the inguinal ligament.
- The renal arteries arise from the aorta at the level of the first lumbar vertebra.
- The diaphragm forms the upper boundary and its crura descend onto the upper lumbar vertebrae.
Great vessels and plexus of the posterior wall
- **Abdominal aorta:** Ends by dividing into common iliac arteries at the fourth lumbar vertebra.
- **Inferior vena cava:** Lies to the right of the aorta, formed by union of the common iliac veins.
- **Lumbar plexus:** Formed in psoas major from L1 to L4. Gives the femoral and obturator nerves.
- **Psoas major:** Flexes the hip; an abscess can track down it into the thigh.
NMC competencies in this chapter
- **AN45.1:** Muscles of the posterior abdominal wall and their nerve supply
- **AN45.2:** Abdominal aorta, inferior vena cava and lumbar plexus
- **AN45.3:** Applied anatomy of the posterior abdominal wall
Frequently Asked Questions
Where does the abdominal aorta end?
It ends at the level of the fourth lumbar vertebra by dividing into the right and left common iliac arteries, a point that can be felt just below and left of the umbilicus.
Why can a psoas abscess appear in the thigh?
The psoas major passes under the inguinal ligament to reach the femur, so pus in its sheath can track down the muscle and form a swelling in the upper thigh.
Where is the lumbar plexus formed?
It is formed within the substance of the psoas major from the ventral rami of the first four lumbar nerves, giving rise to the femoral and obturator nerves among others.
How does this chapter help in NEET-PG?
The great vessels, lumbar plexus and retroperitoneal relations are examined in surgery and radiology, so this wall stays relevant throughout PG preparation.
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