POSTERIOR ABDOMINAL WALL

Three Hiatuses of the Diaphragm:

• Caval Hiatus: Passage for Vena Cava, T8. The highest, most central hiatus, in the central tendon.
• Esophageal Hiatus: T10.
• Aortic Hiatus: The Descending Aorta passes through the diaphragm most posteriorly and inferiorly. T12.
  

Diaphragmatic Crura: Left and Right Crus of the diaphragm, on posterior wall.

• Thoracic Splanchnic Nerves go through the left and right crura of the diaphragm, to enter the abdomen.
  

Lumbocostal Arches (Arcuate Ligaments): The ligaments connecting the diaphragm to the posterior wall. They are condensations of transversalis fascia.

• Median Arcuate Ligament: Passes anterior to the Aorta as it goes through the diaphragm. It creates the Aortic hiatus.
• CLINICAL: At times it can compress the Celiac trunk, below the diaphragm. In this event blood can still circulate via the Pancreaticoduodenal arcade.
• Medial Arcuate Ligament: Overlies the psoas muscle, lateral to the median arcuate ligament.
• It may also be called the psoas fascia.
• RELATION: The sympathetic trunks enter the abdomen immediately posterior to the medial arcuate ligaments.
• Lateral Arcuate Ligament: Ligament around the Quadratus Lumborum muscle. Extends from the transverse fascia of L1 to the 12th rib.
  

Muscles of the Posterior Abdominal Wall:

Psoas Major Muscle: Chief flexor of the thigh and trunk

• Passes all along vertebral column starting at T12.
• Passes deep to the inguinal ligament and attaches to the lesser trochanter of the femur.
• Innervated by L2-L4.
• Contraction: Pulls the body toward the leg, or the thigh toward the body.
  

Iliacus Muscle: Aids the psoas major in flexing the thigh and trunk

• Attaches to the iliac fossa (anterior surface of the iliac bone).
• Inserts into psoas tendon, and hence the two muscles together are often called the iliopsoas muscle.
  

Quadratus Lumborum: Stabilizes the 12th (floating) rib during inspiration.

• Inserts on the 12th rib.
  

Thoracolumbar Fascia: Actually an extension of the aponeuroses of the transversus abdominis and external abdominal oblique muscles.

• It divides into an anterior plane and posterior plane. It thus serves to compartmentalize the muscles, which lies in between the two planes.
• Anterior plane attaches to the transverse process of the lumbar vertebrae.
• Posterior plane attaches to joins with the other muscles in the back.
  

Nerves of the Posterior Wall:

• Things common to all the nerves: CLINICAL
• They are all related to the psoas muscle. Psoas pathology will irritate those nerves. A patient that relieves pain upon relaxation of the psoas muscle may have retroperitoneal pathology.
• All of the nerves pass from the posterior to wall laterally to the anterior wall.
• Subcostal and lumbar plexus pass through the transversalis fascia and then go in-between the transversus abdominis and internal oblique muscles.
• Subcostal Nerve: T12
• Associated with the 12th (floating) rib.
• This nerve is immediately posterior to the kidney and overlies quadratus lumborum muscle.
• It is the only nerve of the lower posterior wall not associated with the lumbar plexus.
  

• Lumbar Plexus: L1-L3, and the upper half of L4.
• These are spinal nerves, so they have somatic and autonomic branches.
• Somatic Components: Supply iliopsoas and quadratus lumborum muscles.
• Autonomic Components: The lumbar splanchnic nerves.
• Location: The plexus itself is located deep within the psoas muscle.
• Distribution: Lower abdominal wall, genitalia, upper portion of the lower limb
• Nerves of the lumbar plexus:
• Iliohypogastric Nerve: T12-L1.
• Runs superomedial to the Anterior Superior Iliac Spine.
• CLINICAL: Passes over McBurney's Point -- the point of surgical entry for an appendectomy (about 1/4 of the way between the ASIS and umbilicus). It can thus be damaged from an appendectomy.
• In the suprapubic region, it divides into two portions: Iliac Branch and Hypogastric Branch.
• Distribution: Iliac branch gets sensory info from hip. Hypogastric branch innervates the suprapubic region.
• Passes posterior to kidney and overlies quadratus lumborum muscle.
• Sometimes it will be joined with the ilioinguinal nerve from their origin at L1, and sometimes it won't.
• Ilioinguinal Nerve: L1
• Same location as the iliohypogastric. It passes through the inguinal canal and emerges out of the inguinal ring.
• Distribution: Innervates the anterior scrotum / labia majora, and the upper and medial thigh.
• CLINICAL: If you want to anesthetize the pubic area, this is one of the nerves you have to block. Anesthesia would probably be placed in the inguinal canal.
• It maybe joined with genitofemoral nerve.
• Passes posterior to kidney and overlies quadratus lumborum muscle.
• Lateral Femoral Cutaneous Nerves: L2-L3
• Associated with the lateral aspect of the psoas muscle.
• Considered to be a part of the posterior division of the plexus. Has nothing to do with the abdominal cavity.
• Innervates the posterior and lateral thigh.

• Femoral Nerve: L2-L4

• By far the largest branch of the lumbar plexus.
• Location: Located in the cleft between the psoas and iliacus muscles.
• Runs posterior to inguinal ligament and carries fascia with it -- the femoral sheath.
• Distribution: Motor innervation of psoas and iliacus; innervation of the thigh and lower extremities.
• Genitofemoral Nerve: L1-L2
• Location: Anterior surface of the psoas muscle. Very fine string, "ribbon."
• Distribution: Branches into the genital and femoral branches.
• Genital branch goes through inguinal nerve to inguinal canal. It innervates the cremaster muscle.
• Femoral Branch: Innervates skin in upper portion of the thigh.
• CLINICAL: Cremaster Reflex: Gently touch the medial portion of the thigh, and see if the scrotum pulls the testes up. This is a simple way of testing the functionality of the lumbar plexus.
  

§ Obturator Nerve: L2(?), L3-L4

• Deep, medial border of the psoas muscle. Very tight chord that passes along the lateral part of the pelvic wall.
  

• Lumbosacral Trunk: L4-L5
  

• Deep and medial to psoas and obturator nerve.
• Distribution = sensory, to the gluteal region, thigh, leg.
• Not part of the lumbar plexus.

Category: Anatomy Notes