Posterior Abdominal Wall - Anatomy

Question 1

What are the 5 muscles of the posterior abdominal wall?

Answer 1

1. Quadratus lumborum
2. Psoas major
3. Psoas minor
4. Iliacus
5. Diaphragm

Question 2

Describe the quadratus lumborum

Answer 2

Located laterally in the posterior abdominal wall.

It is a thick muscular sheet which is quadrilateral in shape.

The muscle is positioned superficially to the psoas major.

Question 3

Where does the quadratus lumborum originate from?

Answer 3

From the iliac crest and iliolumbar ligament.

Question 4

How do the fibres of the quadratus lumborum travel? Where do they insert into?

Answer 4

The fibres travel superomedially, inserting onto the transverse processes of L1 – L4 and the inferior border of the 12th rib.

Question 5

What are the actions of the quadratus lumborum?

Answer 5

Extension and lateral flexion of the vertebral column (antagonist to rectus abdominis)

Question 6

How does the quadratus lumborus act during inspiration?

Answer 6

Fixes the 12th rib during inspiration, so that the contraction of diaphragm is not wasted.

Question 7

What is the quadratus lumborus innervated by?

Answer 7

Anterior rami of T12-L4 nerves

Question 8

Where is the psoas major located?

Answer 8

Located near the midline of the posterior abdominal wall, immediately lateral to the lumbar vertebrae.

Question 9

Where does the psoas major originate from? Where does it attach to?

Answer 9

From the transverse processes and vertebral bodies of T12 – L5.

It then moves inferiorly and laterally, running deep to the inguinal ligament, and attaching to the lesser trochanter of the femur.

Question 10

What are the actions of the psoas major?

Answer 10

Flexion of the thigh at the hip and lateral flexion of the vertebral column.

Question 11

What is the psoas major innervated by?

Answer 11

Anterior rami of L1 – L3 nerves

Question 12

Where is the psoas minor located?

Answer 12

Anterior to the psoas major.

Question 13

Where does the psoas minor originate from?

Answer 13

Vertebral bodies of T12 and L1

Question 14

Where does the psoas minor attach to?

Answer 14

Attaches to a ridge on the superior ramus of the pubic bone, known as the pectineal line

Question 15

What are the actions of the psoas minor?

Answer 15

Flexion of the vertebral column

Question 16

What is the psoas minor innervated by?

Answer 16

Anterior rami of L1 spinal nerve

Question 17

Where is the iliacus muscle located? What does it combine with?

Answer 17

Situated inferiorly on the posterior abdominal wall.

It combines with the psoas major to form the iliopsoas – the major flexor of the thigh.

Question 18

Where does the iliacus muscle originate from?

Answer 18

Originates from surface of the iliac fossa and anterior inferior iliac spine

Question 19

Where does the iliacus muscle insert? What do its fibres combine with before?

Answer 19

Its fibres combine with the tendon of the psoas major

Inserts into the lesser trochanter of the femur.

Question 20

What are the actions of the iliacus muscle?

Answer 20

Flexion of the thigh at the hip joint.

Question 21

What is the innervation of the iliacus muscle?

Answer 21

Femoral nerve (L2 – L4).

Question 22

Which part of the diaphragm is considered to be part of the posterior abdominal wall?

Answer 22

The posterior aspect of the diaphragm

Question 23

What is the psoas sign?

Answer 23

A medical sign that indicates irritation to the iliopsoas group of muscles

Question 24

What is the psoas sign elicited by?

Answer 24

Flexion of the thigh at the hip.

The test is positive if the patient reports lower abdominal pain.

Question 25

What lies between the parietal peritoneum and the muscles of the posterior abdominal wall?

Answer 25

A layer of fascia (sheet of connective tissue)

Question 26

What is this layer of fascia between the parietal peritoneum and the muscles of the posterior abdominal wall continuous with?

Answer 26

The transversalis fascia of the anterolateral abdominal wall.

Question 27

What should be noted about the fascia and its naming?

Answer 27

Whilst the fascia is one continuous sheet, it is anatomically correct to name the fascia according to the structure it overlies.

Question 28

Where is the psoas fascia?

Answer 28

Covers the psoas major muscle

Question 29

Where is the psoas fascia attached to?

Answer 29

It is attached to the lumbar vertebrae medially, continuous with the thoracolumbar fascia laterally and continuous with the iliac fascia inferiorly

Question 30

What does the thoracolumbar fascia consist of?

Answer 30

Three layers; posterior, middle and anterior

Question 31

What muscles are enclosed between the layers of the thoracolumbar fascia?

Answer 31

1. Quadratus lumborum - between the anterior and middle layers.
2. Deep back muscles - between the middle and posterior layers.

Question 32

Where does the posterior layer of the thoracolumbar fascia extend between?

Answer 32

Between the 12th rib and the iliac crest posteriorly.

Question 33

What does the thoracolumbar fascia meet laterally? What does it cover as it forms these attachments?

Answer 33

The internal oblique and transversus abdominis muscles, but not the external oblique.

The latissimus dorsi

Question 34

What is the latissimus dorsi?

Answer 34

The largest muscle in the upper bod

Question 35

What does the anterior layer of the thoracolumbar fascia attach me?

Answer 35

The anterior layer attaches to the anterior aspect of the transverse processes of the lumbar vertebrae, the 12th rib and the iliac crest