L2. Anatomy Of The Posterior Abdominal Wall Flashcards
Describe the Paravertebral gutters
The 5 lumbar vertebrae project into the abdominal cavity quite significantly (sit forwards) and the ribs arch backwards from the vertebral column and then around.
This creates a pair of PARAVERTEBRAL GUTTERS which sit on either side (and behind) of the column.These gutters are floored by powerful longitudinal muscles: these form the posterior abdominal wall.
What are the four major muscles of the posterior abdominal wall?
Psoas Major
Psoas Minor
Quadratus Lumborum
Iliacus Muscle
Where does the pair of psoas major muscles lie? And what is the general shape of the muscle?
It lies in the paravertebral gutter between the bodies and the transverse processes (it overlies the transverse processes) of the lumbar vertebrae.
The lateral border is straight and cuts obliquely through the body.
What are the origins of the psoas major muscle?
Where does the psoas major muscle insert?
It has one continuous origin from the lumbar vertebral column AND the discs AND the medial ends of the transverse processes = high strength
Fibres converge together and pass beneath the inguinal ligament and inserts into the LESSER TROCHANTER of the femer
How far (vertically) does the psoas major muscle span?
Runs from the lower end of T12 to the upper edge of L5
The Psoas Major can be considered a major landmark for the posterior abdominal wall. Why is this so?
- The lumbar plexus is WITHIN psoas major
- The lumbar vessels run BEHIND psoas major
- The Sympathetic trunk, ureter and psoas minor are IN FRONT
What is one of the major functions of the psoas major muscle?
It is an important flexor of the vertebral column (it is weakened in lordosis)
= maintains an erect spine
In what proportion of people does the psoas minor exist in?
In about 2/3 of people - it is phylogenetically degenerating muscle disappearing from the species: doesn’t have many functions
What is the structure of the psoas minor muscle? Where does it insert to?
It is a short, slim belly of muscle and a long and slender tendon on the surface of the psoas major muscle.
It has no real insertion, it blends with the periostium of the pelvis and petters out from there.
Where does the quadratus lumborum sit? And where does it attach to?
Superolaterally (above) the psoas major muscle.
It attaches to the 12th rib above,
to the tips of the transverse processes,
To the posterior half of the ileac crest below
What are the major functions of quadratus lumborum?
It stabilises the 12th rib
It acts as a lateral flexor
Where does the iliacus muscle sit? What is its shape?
Inferior and lateral to the psoas major muscle.
It is an inverted triangle shape
Where does the iliacus muscle attach?
The ilieac bone of the pelvis has a smooth fossa on the internal surface - origin of the iliacus muscle.
It runs edge to edge with psoas major and its fibres converge and pass beneath the inguinal ligament and into the lesser trochanter of the femur
What is important about the relationship between psoas muscle and the ilacus muscle?
They both converge beneath the inguinal ligament into the lesser trochanter of the femur by a COJOINED TENDON called the ILIOPSOAS TENDON
What is each muscle of the posterior wall enclosed by and why?
A dense fascia for firm fixation for the peritoneum
What two muscles of the posterior abdominal wall have their own fascia surrounding them?
Psoas Major
Iliacus
What is the thoracolumbar fascia? What is it made up of?
A complex fascia that has THREE DENSE fascial layers (tri-laminar structure) made up of a tough fibrous tissue
- Posterior: attached to the tip of the spinous process
- Middle: attached to the tip of the transverse process
- Anterior: attached to the anterior surface of the transverse process
What are the two compartments of the thoracolumbar fascia? What makes them and what is contained in them?
The quadratus lumborum is enclosed in the anterior compartment (made by the middle and anterior layers)
The erector spinae muscle is enclosed in the posterior compartment (made by the middle and posterior layer)
What is different about the posterior layer of the fascia?
The posterior lamina/fascia extends the whole extent of the erector spinae muscle - from cervical to sacrum
What is important about the line of fusion of these three layers of the fascia?
All the layers fuse laterally along the line/tip of the 12th rib.
It is a strong vertical fascial structure that gives attachment to the anterior abdominal walls (anchoring transversus abdominas and internal oblique)
(note: external oblique doesn’t attach here because the latissimus dorsi intervenes: instead has a free posterior edge)
What is a psoas abscess? How is this relevant to applied anatomy?
Tuberculosis can present as TB osteomyeitis affecting the vertebral processes. When this occurs in the lumbar spine, the caseous necrosis can break through boney cortex and erupt into the psoas muscle causing a psoas abscess.
But because the fascia is so dense surrounding the psoas, the necrotic tissue is retained in the fascia and tracked down into the groin and presents as a lump in the groin (not in the muscle)
Describe the peritoneum
Parietal layer lining the walls of the abdominal cavity
From various points on the posterior wall, the layer reflects off back to form a series of double layer folds lining the organs = visceral peritoneum
Together these form the MESENTERY
What is the difference between intra- and retro-peritoneal?
Intraperitoneal structures are completely surrounded by peritoneum while retroperitoneal (eg. kidney) have their backs on the posterior abdominal surface and the peritoneum reflects off their anterior surface
Describe the position of the kidneys
Lateral to the vertebral column in the paravertebral gutters
They lie on top (anterior to) the quadratus lumborum muscle
The are classically described as spanning from T12 to L3
Their superior tips lie anterior to the 12th rib
The right kidney is always slightly lower than the left (liver pushes it down)
