*Anatomy: Posterior Abdominal Wall

Question 1

Identify the main posterior abdominal wall muscles.

Answer 1

Quadratus lumborum
Psoas Major
Psoas Minor
Diaphragm
Iliacus

Question 2

QUADRATUS LUMBORUM

• Origin
• Insertion
• Innervation
• Action

Answer 2

QUADRATUS LUMBORUM

• Origin: Inferior border of rib 12, tranverse processes of lumbar vertebrae
• Insertion: Iliolumbar ligament, iliac crest
• Innervation: T12-L4
• Action: Fixes rib 12 during inspiration + lateral flexion (and extension) of the vertebral column

Question 3

PSOAS MAJOR

• Origin
• Insertion
• Innervation
• Action

Answer 3

PSOAS MAJOR

• Origin: Tranverse processes of lumbar vertebrae, bodies of T12-L4 and IV discs
• Insertion: Losser tronchanter
• Innervation: L1-3
• Action: Flexion of the thigh (with iliacus), flexion of the trunk (with iliacus), lateral flexion of the vertebral column

Question 4

PSOAS MINOR

• Origin
• Insertion
• Innervation
• Action

Answer 4

PSOAS MINOR

• Origin: Bodies of T12-L1
• Insertion: Pectineal line and iliopectineal eminence
• Innervation: L1
• Action: weak trunk flexor

Question 5

ILIACUS

• Origin
• Insertion
• Innervation
• Action

Answer 5

ILIACUS

• Origin: Iliac fossa, iliac crest, anterior sacroiliac ligament
• Insertion: Lesser trochanter
• Innervation: Femoral nerve
• Action: Flexion of the thigh (with psoas major)

Question 6

Describe the muscular and vascular compartments in the posterior abdominal wall.

Answer 6

• The space between the inguinal ligament and the hip bone is divided by femoral sheath into muscular and vascular compartments.
• Muscular compartment transmits psoas major and iliacus muscles as well as femoral nerve.
• Vascular compartment transmits femoral vessels.

Question 7

What is the femoral sheath ?

Answer 7

Extension of transversalis fascia

Question 8

State the location of the femoral ring. What is the femoral ring ?

Answer 8

The femoral ring is medial to the vascular compartment.

Femoral ring is the opening of the femoral canal.

Question 9

Identify the boundaries of the femoral canal.

Answer 9

Inguinal ligament (A)
Lacunar ligament (M)
Pectineus or pectineal ligament (P)
Femoral vein (L)

Question 10

What closes the femoral ring ?

Answer 10

Extra-peritoneal tissue closes the femoral canal.

Question 11

Explain how femoral hernias occur.

Answer 11

Femoral ring is a weakened area and often associated with abnormal protrusion of the ab organs into the femoral canal.

Question 12

Explain epidemiology of femoral hernias.

Which of femoral or inguinal hernias is more prone to strangulation ?

Answer 12

Women much more susceptible

Femoral hernias more prone to strangulation than inguinal hernias

Question 13

How may inguinal and femoral hernias be distinguished ?

Answer 13

Use pubic tubercle as landmark

Question 14

Explain the general principles of spinal nerves.

Answer 14

Spinal nerves arise from segments of the spinal cord and emerge as dorsal (posterior) sensory roots and ventral (anterior) motor roots.
The sensory and motor roots combine to form a mixed spinal nerve that passes through an IV foramen and divides into a dorsal and a ventral ramus.

Question 15

Define dermatome. How is each spinal nerve named ?

Answer 15

Region/area of skin supplied by specific spinal nerve.

Each spinal nerve is named in relation to the IV foramen from which it emerges.

Question 16

Define myotome.

Answer 16

Muscle or group of muscles supplied by a specific spinal nerve

Question 17

Which spinal nerves supply the skin and muscles of the abdominal wall ?

Answer 17

Skin and muscles of the abdominal wall are supplied in segments by the ventral rami of spinal nerves T7 to T12 and L1.

Question 18

Describe the course of the spinal nerves which supply the abdomen.

Answer 18

T7 to T12 and L1, start posteriorly. They then travel inferolaterally, then inferomedially , around the abdomen between IO and TA muscles. In their course, give out posterior, lateral and anterior cutaneous branches.
The intercostal nerves (T7-T11) pierce the posterior wall of the rectus sheath to supply rectus abdominis from lateral to medial.
L1 contributes to iliohypogastric and ilioinguinal nerves. Iliohypogastric then pierces external oblique aponeurosis above the superficial inguinal ring, whereas ilioinguinal nerve enters inguinal canal (but not through deep inguinal ring) and emerges through the superficial inguinal ring. The latter two supply the skin just above the inguinal ligament, as well as the inferior fibers of IOs and TA

Question 19

Identify which spinal nerve innervate each specific dermatome, indicating referred pain from where gets to each dermatome.

Answer 19

T6-7: epigastrium (referred pain from stomach and oesophagus)
T10: umbilicus (referred pain from appendix, gonad, and small intestine)
T12: pubic region (referred pain from lower colon, bladder, and uterus)

Question 20

Explain the link between Varicella Zoster (Shingles) virus and dermatomes.

Answer 20

Varicella zoster virus may remain inactive in nerve cells.
Reactivation of the virus causes shingles
The rash forms a band along the course of a nerve (i.e. dermatome), only appearing on one side of the body (skin remains painful until after the rash has gone)

Question 21

What is a possible risk factor for singles ?

Answer 21

Having had chickenpox (i.e. same virus, may now be inactive in nerve cells)

Question 22

What are possible clinical consequences of nerve injury to iliohypogastric or ilioinguinal nerves ?

Answer 22

May weaken IOs and TAs (which are supplied by them), and hence the conjoint tendon (ilioinguinal nerve) and predispose to inguinal hernias.

Question 23

State the location of the lumbar plexus.

Answer 23

Forms in the psoas major muscle, branches of which is visible on the posterior abdominal and pelvic walls.

Question 24

What does the lumbar plexus innervate ?

Answer 24

Lumbar plexus innervates abdominal and some of the lower limb muscles

Question 25

Draw the lumbar plexus.

Answer 25

Refer to slide 19 in lecture on "Posterior Abdominal Wall"

Question 26

What are the major branches of the lumbar plexus (more or less from superior to inferior) ? State the spinal nerve each branch comes from.

Answer 26

* Iliohypogastric (L1) * Ilioinguinal (L1) * Genitofemoral (L1, 2) * Lateral femoral cutaneous (lateral femoral cutaneous nerve of the thigh) (L2, 3) * Obturator (L2, 3, 4) * Femoral (L2, 3, 4) * To lumbosacral trunk (L4)

Question 27

What is another name for the T12 nerve ?

Answer 27

Subcostal nerve

Question 28

Describe the arterial supply of the abdominal wall.

Answer 28

Anastamoses between all the vessels, with the arteries tending to converge towards the umbilicus. 1) IC arteries 2) Lumbar artery (branches of the abdominal aorta) 3) Superior epigastric artery (branch of the internal thoracic artery) 4) Inferior epigastric artery (branch of the external iliac artery) 5) Superficial epigastric artery (branch of femoral artery) 6) Superficial circumflex iliac artery (branch of femoral artery) 7) Deep circumflex iliac artery (branch of external iliac artery)

Question 29

Briefly state the course of the superior epigastric arteries (one of the arterial supplies of the abdominal wall).

Answer 29

Superior epigastric arteries descend behind the rectus abdominis, in the rectus sheath.

Question 30

Briefly state the location and course of the inferior epigastric arteries (one of the arterial supplies of the abdominal wall).

Answer 30

- Inferior epigastric arteries located on the medial side of the deep inguinal ring - Enter the rectus sheath and ascend behind the rectus abdominis

Question 31

Briefly state the course of the deep circumflex iliac arteries (one of the arterial supplies of the abdominal wall).

Answer 31

Deep circumflex iliac arteries run laterally, parallel to the inguinal ligament.

Question 32

Describe the veinous drainage of the abdominal wall.

Answer 32

- All the arteries are accompanied by veins (radiate out of the umbilicus whereas arteries converge towards it) - All these veins eventually drain into the femoral and external iliac veins inferiorly, the internal thoracic and axillary veins superiorly. - Superficial epigastric and superficial circumflex iliac veins can drain into the proximal end of the great saphenous rather than femoral vein - Para-umbilical veins connect the system through the umbilicus to the portal veins of the liver

Question 33

Describe the lymphatic drainage of the abdominal wall.

Answer 33

1) Superficial ANTERIOR Above umbilicus: Anterior axillary nodes Below umbilicus: Superficial inguinal nodes POSTERIOR Above iliac crests: Posterior axillary nodes Below iliac crests: Superficial inguinal nodes 2) Deep Lymph from the deeper abdominal wall is drained by vessels alongside the epigastric vessels. SUPERIORLY, to the parasternal nodes → mediastinal nodes INFERIORLY, to the external iliac nodes → para-aoartic nodes

Question 34

Define Caput Medusae.

Answer 34

"-Appearance of distended and engorged superficial epigastric veins, which are seen radiating from the umbilicus across the abdomen. -Sign of liver disease."

Question 35

What is the clinical significance of the fact that psoas and its sheath arise not only from the lumbar vertebrae but also from their IV discs ?

Answer 35

TB and salmonella discitis (or some other infection) may spread, resulting in infection/abscess into psoas muscle sheath, and spread within the muscle and sheath, and may appear below the inguinal ligament as a mass (in femoral region).

Question 36

Diagnose the following problem: - 27 year old male - Tingling, numbness, and burning pain in the lateral thigh area - Started more than a year ago, when he had a BMI of 38 - Relieved for some time when losing weight but starting again - Wearing tight fitting denim

Answer 36

Meralgia paraesthetica, due to compression of the lateral femoral cutaneous nerve (in this case, by the tight fitting jeans)