Anatomy - Abdomen

Question 1

Label A-H

Answer 1

A, B, C - anterior, middle and posterior layers of the thoracolumbar fascia

D - erector spinae

E - psoas major

F - anterior cutaneous branch

G - free edge of external oblique

H - quadratus lumborum

Question 2

What muscles are found in the anterolateral abdominal wall?

Answer 2

There 5 paired muscles in the anterior abdominal wall, which include:

• Flat Layered Muscles
  
  • External Oblique
  • Internal Oblique
  • Tranversus Abdominis
• Central Vertical Muscles
  
  • Rectus Abdominis
  • Pyramidalis

Question 3

What are the origins, course and insertions of the external oblique muscles?

Answer 3

Origins:

• inferior 8 ribs

Course:

• fibres course infero-medially

Insertions:

• iliac crest
• aponeurosis

Question 4

What are the origins, course and insertions of the internal oblique muscles?

Answer 4

Origins:

• iliac crest
• inguinal ligament
• thoracolumbar fascia

Course:

• fibres course supero-medially

Insertions:

• inferior ribs
• aponeurosis/rectus sheath/linea alba

Question 5

What are the origins, course and insertions of transversus abdominis?

Answer 5

Origins:

• inguinal ligament
• iliac crest
• inferior 6 ribs
• thoracolumbar fascia

Course:

• fibres pass transversely

Insertions:

• aponeurosis

Question 6

What forms the rectus sheath?

Answer 6

The rectus sheath is formed by the aponeuroses of the transversus abdominis, internal oblique and external oblique muscles.

Question 7

What is the linea alba?

Answer 7

A band of connective tissue running vertically in the midline, separating the paired rectus abdominis and pyramidalis muscles.

Question 8

Describe the sensory supply to the abdominal wall.

Answer 8

Innervation arises from the anterior/dorsal rami of spinal nerves T7-L1

• T7-T11 - intercostal nerves
• T12 - subcostal nerve
• L1 - iliohypogastric and ilioinguinal nerve (supplies sensation to genitalia!)

The nerves course anteriorly in the abdominal wall travelling in the layers between the internal obliques and transversus abdomini, pierce rectus abdominis, terminating as the anterior cutaneous branch.

Question 9

What is the principle of the TAP block, and how might you perform it?

Answer 9

A ‘transversus abdominal plane’ block targets the nerves which supply sensation to the abdominal wall, which lie in a plane deep to the internal obliques and superficial to transversus abdominis.

With patient supine a blunt needle is passed perpendicularly to the skin, just cranial to the iliac crest and anterior to latisimus dorsi, piercing the soft tissues and then in turn the aponeuroses of external oblique and internal oblique, felt as successive ‘gives’ in resistance. After the second ‘give’, aspirate the TAP to r/o intravascular placement, and then inject 20mls LA (e.g. 0.25 or 0.5% bupivacaine). An US guided approach can be used, with probe placement in the mid-axillary line half-way between iliac crest and costal margin.