Download Lecture 15 - Posterior Abdominal Wall: Learning Objectives

Lecture 15 - Posterior Abdominal Wall:
 Learning Objectives
 Posterior Abdominal Wall
 Identify the relationships, attachments, innervations and main actions of the following muscles:
 i. psoas major
 ii. iliacus
 iii. quadratus lumborum
 Identify the position, course and relationships of the arteries, veins and lymphatic drainage situated in the
region of the posterior abdominal wall
 Identify the formation, relations and branches of the lumbar and sacral plexuses, with special attention paid
to the peripheral course of the following main terminal branches:
 i. Femoral
 ii. Obturator
 iii. Pudendal
 iv. Sciatic
 v. superior gluteal
 vi. inferior gluteal
 vii. posterior femoral cutaneous
 Identify the effects of a complete lesion of the following nerves:
 i. Sciatic
 ii. Femoral
 iii. Tibial
 iv. superior gluteal
 v. inferior gluteal
 vi. obturator
 vii. common fibular
 viii. superficial fibular
 ix. deep fibular
 Review cutaneous sensory (dermatome) and motor segmental (myotome) innervation
 Identify methods of testing the integrity of the following nerves:
 i. Obturator
 ii. Femoral
 iii. superior gluteal
 iv. inferior gluteal
 v. sciatic
 vi. tibial
 vii. common fibular
Posterior Abdominal Wall
 Mainly composed of:
 5 lumbar vertebrae and associated IV discs
 Posterior abdominal wall muscles, including the psoas, quadratus lumborum, iliacus, etc.
 Diaphragm, which contributes to the superior part of the posterior wall
 Fascia, including the thoracolumbar fascia
 Fat, nerves, vessels (e.g., aorta and IVC), and lymph nodes
 Thoracoabdominal Diaphragm
 Between thoracic and abdominal cavities
 Thin, voluntary muscle
 Dome-shaped
 Origin
 Sternal, costal, vertebral
 Right crus
 L1-L3/4 bodies, IV discs
 Larger than left crus
 Primarily forms esophageal hiatus
 Arcuate ligaments
1. Median
 Unpaired
 Between crura
 Over aortic hiatus
 Insertion
 Central tendon
 Left crus
 L1-L2/3 bodies, IV discs
2. Medial
 Over psoas major
 Innervation
 Phrenic nerves – motor
 Intercostals (T6-T11, subcostal) – sensory to
periphery
 Hiatuses..
1. Caval Hiatus
 Opening in central
tendon, T8 level
 IVC
1.
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
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3. Lateral
 Over quadratrus
lumborum
 Blood Supply
 Superior phrenic – thoracic aorta
 Pericardiacophrenic – internal thoracic
 Musculophrenic – internal thoracic
 Posterior intercostal – thoracic aorta
 Inferior phrenic – abdominal aorta
2. Esophageal Hiatus
 Right crus, T10 level
 Esophagus, vagal
trunks
3. Aortic Hiatus
 Posterior to MnAL,
T12 level
 Aorta, azygos vv., TD
Muscles of the Posterior Abdominal Wall:
Psoas Major (Greek for “muscle of the loin” – Tenderloin! Yum!)
 Lumbar plexus of nerves is embedded in the posterior part of the psoas, anterior to the lumbar transverse
processes
Superior attachment
 Transverse processes of lumbar vertebrae; sides of bodies of T12-L5 vertebrae and intervening
intervertebral disks
Inferior attachment
 Strong tendon to lesser trochanter of femur
Innervation
 Anterior (ventral) rami of L1, L2, L3
Main action
 Acting inferiorly with the iliacus, it flexes thigh
 Acting superiorly, it flexes vertebral column laterally
 Used to balance the trunk (lateral flex trunk)
 When sitting, acts inferiorly with iliacus to flex trunk
2. Psoas Minor
 Origin
 Bodies T12L1
 Insertion
 Iliopubic
eminence
 Action
 Weak flexor
of trunk
 Innervation
 Ventral
ramus L1
3.
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







Iliacus
Large, triangular muscle lying along the lateral aspect of the inferior part of psoas major
Together the psoas and iliacus form the iliopsoas, the chief flexor of the thigh
Stabilizer of the hip joint
Helps maintain the erect posture at hip joint
Psoas and iliacus share in hip flexion, but only psoas can produce movement (flexion/lateral bending) of the
lumbar vertebral column
Superior attachment
 Superior 2/3 of iliac fossa
 Ala of sacrum
 Anterior sacroiliac ligaments
Inferior attachment
 Lesser trochanter of femur and shaft inferior to it; psoas major tendon
Innervation
 Femoral nerve (L2-L4)
Main action
 Flexes thigh
 Stabilizes hip joint
 Acts with psoas major
4. Quadratus Lumborum
 Forms a thick muscular sheet in the posterior abdominal wall
 Post. to kidney
 Branches of the lumbar plexus run inferiorly to the anterior surface of this muscle
 Superior attachment
 Medial half of inferior border of 12th ribs
 Tips of lumbar transverse processes (L1-L4)
 Inferior attachment
 Iliolumbar ligament and internal lip of iliac crest
 Innervation
 Anterior (ventral) rami of T12 and L1-L4 nerves
 Main action
 Extends and laterally flexes vertebral column
 Fixes the 12th rib during inspiration
Fascia of Posterior Abdominal Wall:
 Fascia named according to the structure covered
 Psoas fascia covers the psoas major muscle
 attached medially to the lumbar vertebrae and pelvic
brim
 Psoas fascia (sheath) is thickened superiorly to form
the medial arcuate ligament
 Psoas fascia fuses laterally with the quadratus lumborum
and thoracolumbar fascias
 Inferior to the iliac crest, the psoas fascia is continuous
with the part of the iliac fascia covering the iliacus
Vessels and Lymphatics of the Posterior Abdominal Wall:
 Abdominal Aorta
 Most arteries supplying the posterior abdominal wall arise from the abdominal aorta
 Begins at the aortic hiatus (T12) and ends at L4 by dividing into r. and l. common iliac arteries
 Common iliac arteries run inferolaterally, following the medial border of the psoas muscles to the pelvic
brim
 Each divides into internal and external iliac arteries
 Inferior Vena Cava:
 IVC begins anterior to L5 by union of the common iliac veins
 Ascends on r. side of L3-L5 and on the right psoas major to the
right of the aorta
 Leaves the abdomen by passing through the caval opening in the
diaphragm and enters the thorax at T8
 Veins of the PAW are all tributaries of the IVC except for the left
testicular or ovarian vein (enters the left renal vein instead of
entering the IVC)
 IVC returns poorly oxygenated blood from the lower limbs, most
of the back, the abdominal walls, and the abdominopelvic viscera
 Blood from abdominal viscera passes through portal venous
system and liver before entering the IVC via hepatic veins

Tributaries
 Paired visceral
 Renal veins
 Right gonadal vein
 Left into left renal vein
 Right suprarenal vein
 Left into left renal vein
 Paired parietal
 Inferior phrenic veins
 Lumbar veins (L3 and L4)
 Common iliac veins
 Hepatic veins
 Right, middle, left
 Lymphatic Vessels and Lymph Nodes of PAW
 Parallels arterial supply
 External and internal lymph nodes  Common iliac
lymph nodes  r/l lumbar lymph nodes
 Cisterna chyli: L1/L2
 Lymph from the alimentary tract, liver, spleen, and
pancreas passes along the celiac and superior and
inferior mesenteric arteries to the preaortic lymph nodes
(celiac, superior, and inferior mesenteric nodes)
scattered around the origins of these arteries from the
aorta
 Efferent vessels from these nodes form the intestinal lymphatic trunks
 Participate in the confluence of lymphatic trunks that gives rise to the thoracic duct
Nerves of the Posterior Abdominal Wall:
 Somatic and autonomic components
 Subcostal nerves (anterior rami of T12) arise in the thorax, pass posterior to the lateral arcuate ligaments into
the abdomen, and run inferolaterally on the anterior surface of the quadratus lumborum
 Pass through the transversus abdominus and internal oblique muscles to supply the external oblique and skin
of the anterolateral abdominal wall
 Lumbar Spinal Nerves
 Lumbar spinal nerves (L1-L5) pass from the spinal cord through the IV foramina
inferior to the corresponding vertebrae, then divide into posterior and anterior
rami
 Each ramus contains sensory and motor fibers
 Posterior rami pass posteriorly to supply back muscles and overlying skin
 Anterior rami pass laterally and inferiorly to supply the skin/muscles of the
inferiormost trunk and lower limb
 Lumbar Plexus of Nerves
 Formed anterior to the lumbar transverse processes, within the proximal attachment of the psoas major
 Composed of the anterior rami of L1-L4 nerves
 Branches of the lumbar plexus:
 Ilioinguinal and iliohypogastric nerves
 Femoral nerve (L2-L4)
(L1)
 Obturator nerve (L2-L4)
 Genitofemoral nerve (L1, L2)
 Accessory obturator nerve (L3, L4)
 Lateral cutaneous nerve of the thigh
 Lumbosacral trunk (L4, L5
(L2, L3)
 Lumbar Plexus:
 Femoral nerve (L2-L4)
 Emerges from lateral border of psoas major and innervates the iliacus and passes deep to the inguinal
ligament/iliopubic tract to the anterior thigh, supplying the flexors of the hip and extensors of the knee
 Lateral cutaneous nerve of the thigh (L2, L3)
 (Or lateral femoral cutaneous nerve) runs inferolaterally on the iliacus and enters the thigh deep to the
inguinal ligament/iliopubic tract, just medial to the ASIS
 Supplies skin on the anterolateral surface of the thigh
 Obturator nerve (L2-L4)
 Emerges from medial border of psoas major and passes into the lesser pelvis, passing inferior to the
superior pubic ramus (through the obturator foramen) to the medial thigh, supplying the adductor
muscles
 Accessory obturator nerve (L3, L4)
 Present ~10% of the time
 Parallels the medial border of the psoas, anterior to the obturator nerve, crossing superior to the superior
pubic ramus in close proximity to the femoral vein
 Lumbosacral trunk (L4, L5)
 Passes over the ala (wing) of the sacrum and descends into the pelvis to participate in the formation of the
sacral plexus with the anterior rami of S1-S4 nerves
 Ilioinguinal and iliohypogastric nerves (L1)
 Arise from anterior ramus of L1, entering the abdomen posterior to the medial arcuate ligament and passing
inferolaterally, anterior to the quadratus lumborum. Run superior and parallel to the iliac crest, piercing the
transversus abdominis near the ASIS
 Then pass through the internal and external obliques to supply the abdominal muscles and skin of the
inguinal and pubic regions. Division of the L1 anterior ramus may occur as far distally as the ASIS so that
often only one nerve (L1) crosses the posterior abdominal wall instead of two
 Genitofemoral nerve (L1, L2)
 Pierces the psoas major and runs inferiorly on its anterior surface, deep to the psoas fascia
 Divides lateral to the common and external iliac arteries into femoral and genital branches
 Obturator Test: Medial Thigh Adduction
 Obturator nerve is vulnerable to injury during surgery (e.g., removal of cancerous lymph nodes from lateral
pelvic wall)
 Injury causes painful spasms of the adductor muscles of the thigh; also sensory deficits of medial thigh
 Sacral Plexus
 Located on the posterolateral wall of the lesser pelvis
 Two main nerves from it: sciatic and pudendal nerves
 Lie external to the parietal pelvic fascia
 Most branches of the sacral plexus leave pelvis through greater sciatic foramen
 During childbirth, fetal head may compress the nerves of the mother’s sacral plexus, producing lower limb pain
 Sciatic Nerve
 Largest nerve in the body
 Formed as the large anterior rami of spinal nerves L4-S3 converge on the anterior surface of the piriformis
 Passes through greater sciatic foramen
 Supplies posterior thigh, entire leg and foot
 Articular branches to hip joint
 Muscular branches to flexors of knee in thigh and all muscles in leg and foot
 2 major divisions: tibial nerve and common fibular nerve bound in a connective tissue sheath
 Usually separate in the distal thigh
 Pudendal Nerve
 Main nerve of the perineum, chief nerve of the external genitalia
 Leaves the pelvis through the greater sciatic foramen between the piriformis and coccygeus muscles
 S2, S3, S4 origin
 Distribution: structures of the perineum
 Sensory to genitalia
 Muscular branches to perineal muscles, external urethral sphincter, and external anal sphincter
 Superior & Inferior Gluteal Nerves
 Superior gluteal nerve leaves pelvis through greater sciatic foramen
 Origin: L4, L5, S1
 Distribution: Gluteus medius and gluteus minimus muscles
 Inferior gluteal nerve leaves pelvis through greater sciatic foramen, superficial to sciatic nerve,
accompanying inferior gluteal artery
 Origin: L5, S1, S2
 Distribution: Gluteus maximus
 Posterior Cutaneous Nerve of Thigh
 Origin: Sacral plexus (anterior and posterior divisions of anterior rami, S1-S3)
 Supplies more skin than any other cutaneous nerve
 S2-S3 fibers supply skin of perineum via perineal branch
 S1-S2 fibers supply inferior buttock via inferior clunial nerves
 Other fibers supply skin of posterior thigh, proximal leg
 Main part of this nerve lies deep to the deep fascia, with only terminal branches reaching the skin
 Cutaneous Nerves of Lower Limb
 Dermatomes of Lower Limb
 Myotomes: Segmental Innervation of Muscle Groups and Lower Limb Movements:
 Effects of Lesions on the Following Nerves:
 Testing…One, Two:
 Testing Nerve Integrity:
 Femoral: assess hip flexion, leg extension
 Obturator: assess thigh adduction
 Sciatic: assess knee flexion
 Common fibular: assess ankle dorsiflexion
 Tibial: assess ankle plantar flexion
 Inferior gluteal: extends and laterally rotates the thigh at the hip; upper fibers help abduct the thigh; inferior
fibers stabilize the extended knee
 Injury to this nerve leads to a gluteus maximus lurch
 when gluteus maximus is weak/injured, trunk extends (lean back) on heel-strike on weakened side
 compensates for weakness of hip extension
 Injury to Superior Gluteal Nerve
 When a person who has suffered a lesion of the superior gluteal nerve is asked to stand on one leg, the
pelvis on the unsupported side descends indicating that the gluteus medius and minimus on the supported
side are weak or non-functional
 This sign is referred to as a positive Trendelenburg test
 Other causes of this sign include fracture of the greater trochanter (the distal attachment of the gluteus
medius) and dislocation of the hip joint
 Gluteus Medius/Minimus Impairment: Sup. Gluteal Nerve
Key Concepts:
 Muscles: psoas major, iliacus, quadratus lumborum
 Origin, insertion, action, innervation
 Lumbar plexus: femoral nerve, lateral femoral cutaneous nerve, obturator nerve
 Origin, distribution, and function
 What happens when things go wrong
 Sacral plexus: sciatic (common fibular and tibial divisions), pudendal, inferior and superior gluteal, and posterior
cutaneous thigh nerves
 Origin, distribution, and function
 What happens when things go wrong
 Trendelenberg test
 Main concepts of arterial, venous, and lymphatic supply to the posterior abdominal wall