POSTERIOR ABDOMINAL WALL

Three Hiatuses of the Diaphragm:

Caval Hiatus: Passage for Vena Cava, T8. The highest, most central hiatus, in the central tendon.

Eosphageal 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 enters 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 components.

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. It contains all of the nerves below.

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

Assoc 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.