*Anatomy: Posterior Abdominal Wall Flashcards
Identify the main posterior abdominal wall muscles.
Quadratus lumborum Psoas Major Psoas Minor Diaphragm Iliacus
QUADRATUS LUMBORUM
- Origin
- Insertion
- Innervation
- Action
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
PSOAS MAJOR
- Origin
- Insertion
- Innervation
- Action
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
PSOAS MINOR
- Origin
- Insertion
- Innervation
- Action
PSOAS MINOR
- Origin: Bodies of T12-L1
- Insertion: Pectineal line and iliopectineal eminence
- Innervation: L1
- Action: weak trunk flexor
ILIACUS
- Origin
- Insertion
- Innervation
- Action
ILIACUS
- Origin: Iliac fossa, iliac crest, anterior sacroiliac ligament
- Insertion: Lesser trochanter
- Innervation: Femoral nerve
- Action: Flexion of the thigh (with psoas major)
Describe the muscular and vascular compartments in the posterior abdominal wall.
- 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.
What is the femoral sheath ?
Extension of transversalis fascia
State the location of the femoral ring. What is the femoral ring ?
The femoral ring is medial to the vascular compartment.
Femoral ring is the opening of the femoral canal.
Identify the boundaries of the femoral canal.
Inguinal ligament (A) Lacunar ligament (M) Pectineus or pectineal ligament (P) Femoral vein (L)
What closes the femoral ring ?
Extra-peritoneal tissue closes the femoral canal.
Explain how femoral hernias occur.
Femoral ring is a weakened area and often associated with abnormal protrusion of the ab organs into the femoral canal.
Explain epidemiology of femoral hernias.
Which of femoral or inguinal hernias is more prone to strangulation ?
Women much more susceptible
Femoral hernias more prone to strangulation than inguinal hernias
How may inguinal and femoral hernias be distinguished ?
Use pubic tubercle as landmark
Explain the general principles of spinal nerves.
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.
Define dermatome. How is each spinal nerve named ?
Region/area of skin supplied by specific spinal nerve.
Each spinal nerve is named in relation to the IV foramen from which it emerges.
Define myotome.
Muscle or group of muscles supplied by a specific spinal nerve
Which spinal nerves supply the skin and muscles of the abdominal wall ?
Skin and muscles of the abdominal wall are supplied in segments by the ventral rami of spinal nerves T7 to T12 and L1.
Describe the course of the spinal nerves which supply the abdomen.
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
Identify which spinal nerve innervate each specific dermatome, indicating referred pain from where gets to each dermatome.
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)
Explain the link between Varicella Zoster (Shingles) virus and dermatomes.
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)
What is a possible risk factor for singles ?
Having had chickenpox (i.e. same virus, may now be inactive in nerve cells)
What are possible clinical consequences of nerve injury to iliohypogastric or ilioinguinal nerves ?
May weaken IOs and TAs (which are supplied by them), and hence the conjoint tendon (ilioinguinal nerve) and predispose to inguinal hernias.
State the location of the lumbar plexus.
Forms in the psoas major muscle, branches of which is visible on the posterior abdominal and pelvic walls.
What does the lumbar plexus innervate ?
Lumbar plexus innervates abdominal and some of the lower limb muscles
Draw the lumbar plexus.
Refer to slide 19 in lecture on “Posterior Abdominal Wall”
What are the major branches of the lumbar plexus (more or less from superior to inferior) ? State the spinal nerve each branch comes from.
- 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)
What is another name for the T12 nerve ?
Subcostal nerve
Describe the arterial supply of the abdominal wall.
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)
Briefly state the course of the superior epigastric arteries (one of the arterial supplies of the abdominal wall).
Superior epigastric arteries descend behind the rectus abdominis, in the rectus sheath.
Briefly state the location and course of the inferior epigastric arteries (one of the arterial supplies of the abdominal wall).
- Inferior epigastric arteries located on the medial side of the deep inguinal ring
- Enter the rectus sheath and ascend behind the rectus abdominis
Briefly state the course of the deep circumflex iliac arteries (one of the arterial supplies of the abdominal wall).
Deep circumflex iliac arteries run laterally, parallel to the inguinal ligament.
Describe the veinous drainage of the abdominal wall.
- 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
Describe the lymphatic drainage of the abdominal wall.
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
Define Caput Medusae.
“-Appearance of distended and engorged superficial epigastric veins, which are seen radiating from the umbilicus across the abdomen.
-Sign of liver disease.”
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 ?
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).
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
Meralgia paraesthetica, due to compression of the lateral femoral cutaneous nerve (in this case, by the tight fitting jeans)
