The posterior abdominal wall, aorta, IVC and nervous supply to the abdomen

Question 1

What are the components of the posterior abdominal wall

Answer 1

• Made up of the 5 lumbar vertebrae, and in front of these the IVC and aorta
o To the left and right of the IVC and aorta- the deep paravertebral gutters
o Paravertebral gutters floored by psoas and quadratus lumborum and the below the iliac crest- the iliacus muscles
o Crura of the diaphragm constitutes the final part

Question 2

Origins, insertions and relations of psoas major

Answer 2

• Location: lies in the gutter of the vertebral bodies and their transverse processes
• Origin: as fibrous arches from the the discs above the 5 lumbar vertebrae (IE T12/L1 to L4/5), associated lumbar vertebral bodies and medial aspects of their transverse processes
• Passage: over the pelvic brim, under the inguinal ligament
• Attachment: lesser trochanter of femur
• Relations: The lumbar plexus is embedded within and the external vertebral venous plexus is behind it (and in front of the transverse process)
o The genitofemoral nerve emerges from Infront of the muscle,
o the iliohypogastric, ilioinguinal, lateral femoral cutaneous and femoral emerge from its lateral border
o the obturator and lumbosacral trunk from its medial border
o the 4 lumbar arteries and veins pass beneath the 4 arches and run laterally behind the psoas and are accompanied by sympathetic rami
Innervation: first three lumbar nerves – mainly L2

Question 3

What is the psoas fascia and medial arcuate ligament?

Answer 3

• the psoas fascia invests the muscle, and attaches to the vertebral bodies, fibrous arches and transverse process and extends along to the pelvic brim where it attaches to the iliopubic eminence at the margin of the muscle
o not part of the lumbar fascia but its lateral edge blends with the anterior layer of the lumbar fascia
o the medial arcuate ligament is a thickening of the psoas fascial curving obliquely from the body of L1 (or L2) to the transverse process of L1- its fibresz arise from the crus of the diaphragm and psoas above this is in the thorax
 the sympathetic trunk passes from the thorax to the abdomen beneath this ligament

Question 4

Origins, insertions and nervous innervation of psoas minor?

Answer 4

• only present in 2/3
• lies on the surface of psoas major
• origin: its short belly arises from T12 and L1 vertebrae, becoming a long tendon, which flattens and blends with the psoas fascia behind the inguinal ligament, giving it a bony attachment to the arcuate line and iliopubic eminence
• supply: L1 nerve
• action: weak lumbar flexor

Question 5

Origins, insertions and innervation of quadratus lumborum?

Answer 5

• lies lateral to the psoas major and medial to the transversus abdominus -edge to edge with these
• it lies in the anterior compartment of the lumbar fascia
• origins: transverse process of L5, iliolumbar ligament and adjoining iliac crest
• insertions transverse process of upper 4 lumbar vertebrae lateral to the psoas and the inferior border of the medial part of the 12th rib
• its lateral border slopes upwards and medially and crosses the iliocostalis
• covered anteriorly by the anterior layer of the lumbar fascia
• Nerve: T12 and the upper 3-4 lumbar nerves

Question 6

What is the lateral arcuate ligament?

Answer 6

• the lateral arcuate ligament: is a thickening of the lumbar fascia between the first lumbar transverse process and 12th rib
o fibres from the diaphragm arise in continuity with this
o the subcostal neuromuscual bundle (VAN) emerges from the thorax beneath the ligament and slopes across the lumbar fascia