Muscles of the Posterior Abdominal Wall

Question 1

What are the parts of the diaphragm?

Answer 1

• central tendon

- muscular part

Question 2

What structures are included on the abdominal aspect of the diaphragm?

Answer 2

• right crus
• left crus
• median arcuate ligament
• medial arcuate ligament
• lateral arcuate ligament

Question 3

Describe the right crus of the diaphragm.

Answer 3

• originates from the upper three lumbar vertebrae
• splits to surround the esophagus
• weakness in the right crus can cause hiatal hernia

Question 4

Describe the left crus of the diaphragm.

Answer 4

• originates from the upper two lumbar vertebrae

- smaller and shorter than the right crus

Question 5

Describe the median arcuate ligament of the diaphragm.

Answer 5

a thickening of fascia which connects the right crus to the left crus, and forms the border of the aortic hiatus

Question 6

Describe the medial arcuate ligament of the diaphragm.

Answer 6

• a thickening of fascia which connects the body of the 1st lumbar vertebra to the transverse process of the 1st lumbar vertebra
• passes over the psoas major muscle and sympathetic trunk

Question 7

Describe the lateral arcuate ligament of the diaphragm.

Answer 7

• a thickening of fascia which connects the transverse process of the 1st lumbar vertebra to the 12th rib
• passes over the quadratus lumborum muscle

Question 8

What is the origin, insertion, nerve supply, and function of the psoas major muscle?

Answer 8

• O: transverse processes and bodies of T12 to L5 and corresponding intervertebral discs
• I: lesser trochanter
• N: lumbar nerves 1-3
• F: flexes thigh, flexes trunk

Question 9

What is the origin, insertion, nerve supply, and function of the psoas minor muscle?

Answer 9

• O: bodies and intervertebral disks of T12 to L1
• I: pecten pubis, iliopubic eminence
• N: 1st lumbar nerve
• F: flexes trunk

Question 10

What percentage of people is the psoas minor muscle present in?

Answer 10

60%

Question 11

What is the origin, insertion, nerve supply, and function of the iliacus muscle?

Answer 11

• O: iliac fossa, iliac crest, ala of sacrum
• I: lesser trochanter via tendon of psoas major
• N: branches of femoral nerve (L2, L3)
• F: flexes thigh, tilts pelvis forward

Question 12

What is the psoas sign?

Answer 12

• pain produced when the thigh is extended passively or if the patient flexes his/her hip
• positive right psoas sign suggests appendicitis

Question 13

What is the common tendon for the psoas major, psoas minor, and iliacus?

Answer 13

iliopsoas tendon

Question 14

What is the origin, insertion, nerve supply, and function of the quadratus lumborum muscle?

Answer 14

• O: iliolumbar ligament, iliac crest
• I: 12th rib, transverse processes of L1-4
• N: subcostal nerve, lumbar nerves 1-4
• F: depresses 12th rib (during coughing/forced expiration), flexes trunk laterally