The posterior abdominal wall is composed of bone, muscle, and fascia. It extends from the lowest ribs to the pelvic brim. Key structures include the lumbar vertebrae, psoas major muscle, quadratus lumborum muscle, and several layers of fascia. The lumbosacral triangle of Marcille on each side of the L5 vertebrae contains major blood vessels and nerves. The psoas major acts to flex the hip and trunk. Fascia layers including the fascia iliaca cover and separate muscles of the posterior abdominal wall.

1. POSTERIOR
ABDOMINAL WALL
DR. SUNDIP CHARMODE
ASSOCIATE PROFESSOR
DEPARTMENT OF ANATOMY
AIIMS RAJKOT

2. COMPOSITION
• Osseo-musculo-fascial and extends from the last rib to the pelvic brim.
• Bony part:
• Middle line - Bodies of five lumbar vertebrae
• Above and laterally: inner surface of lower ribs
• Below and laterally: iliac fossae and ale of sacrum
• Muscular part: muscles occupy the paravertebral gutter, and named
from medial to lateral- psoas major, quadratus lumborum, aponeurotic
origin of transversus abdominis
• Fascial part: Fascia Iliaca covers psoas and ilacus. Anterior and
middle layers of Thoraco-lumbar fascia encloses quadratus lumborum.

5. LUMBO-SACRAL TRIANGLE
OF MARCILLE
• Triangular interval on each side of the body of fifth
lumbar vertebra.
• Medially: body of fifth lumbar vertebra
• Laterally: medial border of psoas major muscle
• Apex: directed above and below by junction of psoas
and body of fifth lumbar vertebra
• Base: upper surface of lateral mass or ala of the
sacrum
• Floor or posterior wall: transverse process of fifth
lumbar vertebra and ilio-lumbar ligament.

6. CONTENTS OF TRIANGLE
• Structures of the deep stratum: run
vertically over the ala of sacrum
• Ganglionated sympathetic trunk
• Lumbo-sacral trunk
• Ilio-lumbar artery
• Obturator nerve
• Structures of the Intermediate
stratum: pass obliquely downwards
and laterally
• Common iliac artery dividing into
external and internal iliac arteries
• Common iliac vein formed by union of
external and internal iliac veins

7. CONTENTS OF TRIANGLE
• Structures of the superficial stratum:
cross vertically in from of oblique
structures
• The ureter crosses the common iliac
vessels at the lateral angle of the triangle
• The ovarian vessels crosses the internal
iliac vessels (lateral to the ureter)and enter
the suspensory ligament of the ovary.
• The inferior mesenteric vessels traverse
the pelvic inlet in front of the common
iliac vessels
• The nerve fivers from the hypogastric
plexuses ascend in front of the common
iliac vessels.

8. PSOAS MAJOR
• Long fusiform muscle
• Covered together with the iliacus by the fascia
iliaca.
• Origin:
• Anterior surfaces and lower borders of
transverse processes of all lumbar vertebrae
• Five fleshy slips from the bodies and
intervertebral discs of all lumbar vertebra
• Four tendinous arches bridging across the
sides of the bodies of lumbar vertebrae
• Insertion: anterior surface of the tip of lesser
trochanter of the femur

9. PSOAS MAJOR
• Nerve supply: ventral rami of 2nd and 3rd lumbar
nerves
• Action:
• Chief flexor of hip joint (acting from above)
• Flexes the trunk at the hip joint
• When the foot is on ground, it acts as a medial
rotator of hip joint
• When the foot is off the ground, it acts as a lateral
rotator of hip joint

12. FASCIA ILIACA
• It is a strong sheet of fascia which covers
the iliacus and psoas major and encloses
them in a closed osseo-fascial pocket.
Two parts:
• Iliac part – which covers both the iliacus
and psoas major below the iliac crest
• Psoas part – covers only the psoas major
above the iliac crest

13. FASCIA ILIACA
ATTACHMENT OF ILIAC PART
• Laterally: Inner lip of ventral
segment of iliac crest where it
blends with fascia transversalis
• Medially: Alae of sacrum and
pelvic brim up to ilio-pubic
eminence
• Above: Continuous with psoas part
• Below:
ATTACHMENT OF PSOAS PART
• Above: thickened to form medial
arcuate ligament
• Laterally: it is attached to the
anterior surface of transverse
processes of lumbar vertebrae,
where it blends with thoraco-
lumbar fascia
• Medially: bodies and discs of
lumbar vertebra

14. FASCIA ILIACA
STRUCTURES PIERCING FASCIA ILIACA
• In front: Genito-femoral nerve
• Laterally: Ilio-hypogastric and ilio-
inguinal nerves and the fourth
lumbar artery
• Medially: Lumbo-sacral trunk, ilio-
lumbar artery and obturator nerve
CLINICAL CORRELATES
• An abscess may collect beneath
the fascia iliaca from the
tuberculous disease of the lumbar
vertebrae.

15. QUADRATUS LUMBORUM
• Quadrilateral muscle
• Fills up the gap between the last rib and the iliac
crest
• It is enclosed between anterior and middle
layers of the thoraco-lumbar fascia.
• Origin:
• Posterior one-third of inner lip of ventral segment of
iliac crest
• Ilio-lumbar ligament
• Insertion:
• Fleshy fibers, attached to lower border and
anterior surface of medial part of 12th rib
• Tendinous fibers attached to the anterior surface of
transverse processes of upper four lumbar
vertebrae.

16. QUADRATUS LUMBORUM
• Nerve supply: ventral rami of 12th
thoracic and upper three or four
lumbar nerves
• Actions:
• It fixes the last rib and helps the
diaphragm during inspiration.
• Acting on one side it acts as lateral
flexor of trunk
• Acting on both sides they produce
extension of the vertebral column.

17. THORACO-LUMBAR FASCIA
In lumbar region, the fascia
consists of three layers: Anterior,
Middle and posterior.
The layers enclose 2 spaces.
Quadratus lumborum between
anterior and middle layers.
Erector spinae between middle
and posterior layers.

18. ANTERIOR LAYER OF THORACO-LUMBAR
FASCIA
• It covers the anterior surface of the Quadratus lumborum and
presents following attachments:
• Above: thickened to form lateral arcuate ligament
• Below: attached to posterior part of iliac crest and is thickened to form
the ilio-lumbar ligament
• Medially: attached to a vertical ridge on the anterior surface of
transverse process of lumbar vertebrae where it blends with the psoas
fascia.
• Laterally: blends with the middle layer of lumbar fascia at the lateral
border of the quadratus lumborum

19. MIDDLE LAYER OF THORACO-LUMBAR FASCIA
• It covers the posterior surface of the Quadratus lumborum and
presents following attachments:
• Above: attached to the lower border of 12th rib and is thickened to form
lumbo-costal ligament which extends from lower border of 12th rib to
transverse process of L1 vertebra.
• Below: attached to posterior part of iliac crest and is thickened to blends
with the ilio-lumbar ligament
• Medially: attached to the tips of transverse process of lumbar vertebrae and
to inter-transversus muscles between the vertebrae.
• Laterally: blends with the anterior layer at the lateral border of the
quadratus lumborum and with the posterior layer at the lateral border of
erector spinae.

20. POSTERIOR LAYER OF THORACO-LUMBAR
FASCIA
• It covers the posterior surface of the Erector spinae and presents
following attachments:
• Above: It enters the back of thorax and is attached medially to the
spines of the thoracic vertebrae and laterally to the angles of the ribs.
• Below: attached to dorsal surface of the sacrum and dorsal segment of
the iliac crest in ‘U’ shaped manner.
• Medially: spines and supra-spinous ligaments of lumbar vertebrae.
• Laterally: blends with the middle layer of lumbar fascia.

21. MUSCLES ATTACHED TO THE THORACO-
LUMBAR FASCIA
1. From the anterior layer: a few fibers of the diaphragm.
2. From the fusion of the anterior and middle layers – transversus
abdominis and internal oblique
3. From posterior layer – latissimus Dorsii, serratus posterior inferior,
a few fibers of gluteus maximus

22. LYMPHATICS OF POSTERIOR ABDOMINAL WALL
• Lymph draining the abdominal wall and most of the abdomino-pelvic
organs, except a part of liver drain into Thoracic duct.
• Outlying lymph nodes: (close to the wall of the target organs) – para-
cardiac, gastric, gastro-epiploic, pyloric, cystic, etc.
• Intermediate nodes: (accompany the branches of aorta) – internal
iliac, external iliac, hepatic, left gastric, etc.
• Terminal group (around abdominal aorta) – preaortic, lateral aortic
and retro-aortic

24. NERVES OF POSTERIOR ABDOMINAL WALL
• The innervations of the abdomen are derived from the somatic spinal
nerves and the autonomic nerves.

34. THANK YOU