Download 1 Structure of the Thoracic Wall A. Sternum 1

1
Structure of the Thoracic Wall
A. Sternum
1. Location: midline of the anterior chest wall
2. Divided into three parts
a. Manubrium
i. Location: opposite T3, T4 vertebrae
ii. Articulates with:
A. Body of the sternum (see 3.a.)
B. Clavicles
C. 1st costal cartilage and the superior part of the 2nd costal cartilage
b. Body of the sternum
i. Articulates with:
A. Manubrium (see 3.a.)
B. 2nd to 7th costal cartilages
C. Xiphoid process (see 3.b.)
c. Xiphoid process
i. Location: opposite T9 vertebral body
ii. Articulates with:
A. Body of the sternum (see 3.a.)
iii. Thin plate of cartilage
iv. Proximal end becomes ossified during adult life
3. Joints of the sternum
a. Manubriosternal joint
i. Location: opposite the T4-T5 intervertebral disc
ii. Sternal angle describes the palpable traverse ridge marking the joint, lying in
between the two facets for the second costal cartilages
iii. Cartilaginous joint
iv. Movement: small amount during respiration
b. Xiphisternal joint
i. Location: opposite the body of the T9 vertebrae
ii. Cartilaginous joint
iii. Fuses with the body of the sternum during middle age
4. Clinical correlations
a. Marrow biopsy
i. Marrow cavity of sternum rich in red hematopoietic marrow throughout life
b. Median sternotomy
i. Vertical incision along the sternum to gain access to the heart, lungs, and great
vessels
B. Ribs
1. Anterior attachment
a. True ribs (superior 7 pairs): via costal cartilages to sternum
b. False ribs (8th-10th pairs): to each other, and via costal cartilages to the 7th rib
c. Floating ribs (11th-12th pairs): no anterior attachment
2. Components of a typical rib
a. Head
i. Two facets articulate with the numerically corresponding, and the immediately
superior, vertebral body
b. Neck
i. Constricted portion between the head and the tubercle
c. Tubercle
i. Prominence on the outer surface of the rib at the junction of the rib and shaft
ii. Facet for articulation with the numerically corresponding transverse process
d. Shaft
i. Thin and flatted and twisted on its long axis
ii. Inferior border has a costal groove
e. Angle
i. Where the shaft of the rib bends sharply forward
3. Atypical rib-1st rib
a. Small and flattened superiorly
b. Muscular attachements
i. Scalenus anterior: attached to the superior surface and inner border
c. Relations
i. Subclavian v. crosses the rib anterior to the scalenus anterior m.
ii. Subclavian a. and lower trunk of the brachial plexus cross the rib posterior to the
scalenus anterior m.
4. Costal Cartilages
a. Contribute to the elasticity and the mobility of the thoracic wall
i. Flexibility is lost during old age as a result of superficial calcification
b. 11th and 12th ribs end in the abdominal musculature
5. Joints of the ribs
a. Joints of the head of the ribs
i. 1st rib and the inferior 3 ribs have a single synovial joint with their corresponding
vertebral body
ii. 2nd to 9th ribs have synovial joint with the numerically corresponding, and the
immediately superior, vertebral body
1. Intra-articular lig. connects the head to the intervertebral disc
b. Joints of the tubercles of the ribs
i. Articulate by means of synovial joints with the numerically corresponding transverse
process (absent in the 11th-12th ribs)
c. Joints of the ribs and costal cartilages
i. Cartilaginous joint with no movement possible
d. Joints of the costal cartilages with the sternum
i. 1st costal cartilage-manubrium joint is cartilaginous, hence no movement possible
ii. 2nd-7th costal cartilage-lateral border of sternum joints are synovial
iii. 6th-10th costal cartilage articulate with each other along their borders via small
synovial joints
iv. 11th-12th costal cartilages are embedded in the abdominal musculature
C. Thoracic Cavity
1.
D. Intercostal Spaces
1. Musculature
a. External intercostal muscle
i. Most superficial layer, fibers directed downward and forward
ii. Attachments: inferior border of the superior rib -> superior border of the inferior rib
iii. Muscle extends forward to the costal cartilage, where it is replaced by the anterior
(external) intercostal membrane
b. Internal intercostal muscle
2.
3.
i. Intermediate layer, fibers directed downward and backward
ii. Attachments: subcostal groove of the superior rib -> superior border of the inferior
rib
iii. Muscle extends backward from the sternum to the angles of the ribs, where it is
replaced by the posterior (internal ) intercostal membrane
c. Innermost intercostal muscle
i. Deepest layer
ii. Relations
1. Internally: endothoracic fascia and the parietal pleura
2. Externally: intercostal neurovasculature
d. Action of the intercostal muscles
e. Innervation of the intercostal muscles
i. Corresponding intercostal nerves
Vasculature
a. Intercostal arteries and veins
i. Posterior intercostal arteries
1. 1st-2nd spaces: subclavian a. -> costocervical trunk -> superior intercostal a. ->
post. intercostal arteries
2. 3rd-11th spaces: descending thoracic aorta -> post. intercostal arteries
ii. Anterior intercostal arteries
1. 1st-6th spaces: subclavian a. (1st part) -> intercostal thoracic artery -> anterior
intercostal arteries
2. 7th-11th spaces: internal thoracic artery -> musculophrenic artery -> anterior
intercostal arteries
b. Intercostal arteries supply branches to the muscles, skin, and parietal pleura
i. Branches are particularly large to the superficial structures in the breast region in
females
c. Posterior intercostal veins -> azygos or hemiazygous veins
d. Anterior intercostal veins -> internal thoracic and musculophrenic veins
Nerves
a. Intercostal nerves
i. Anterior rami of the 1st-11th thoracic spinal nerves
ii. Anterior ramus of the 12th thoracic spinal nerves runs forward in the abdominal wall
as the subcostal nerve
iii. Path
1. Enters space between parietal pleura and the posterior intercostal membrane
2. Runs inferior to intercostal vessels in the subcostal groove between the
innermost intercostal and internal intercostal muscle
a. 1st-6th nerves distribute within the intercostal spaces
b. 7th-9th nerves pass deep to the costal cartilages to enter the anterior
abdominal wall
c. 10th-11th nerves pass directly into the abdominal wall (as ribs are
floating)
iv. Branches
1. Rami communicantes
a. Connect the intercostal nerve to a ganglion of the sympathetic
trunk
2. Collateral branch
a. Runs forward inferiorly to the main nerve, superior to the upper
border of the rib below
3. Lateral cutaneous branch
a. Cutaneous supply of the side of the chest
b. Divides into anterior and posterior branch
c. Exceptions
i. 1st lat. cut. branch: contributes to the brachial plexus
ii. 2nd lat. cut. branch (intercostobrachial nerve): contributes
to the medial cutaneous nerve of the arm
4. Anterior cutaneous branch
a. Terminal portion of the main trunk
b. Cutaneous supply near the midline
c. Divides into medial and lateral branch
Muscular branches
a. Supplies the intercostal muscles
6. Pleural sensory branches
a. Runs to the parietal pleura
7. Peritoneal sensory branches (7th-11th intercostal nerves)
a. Runs to the parietal peritoneum
v. 1st-6th intercostal nerves supply the skin and parietal pleura covering the outer and
inner surfaces of the intercostal space, intercostal muscles, and levatores costarum
and serratus posterior muscle
vi. 7th-11th intercostal nerves supply the skin and the parietal peritoneum covering the
outer and inner surfaces of the abdominal wall, and the anterior abdominal muscles
E. Endothoracic fascia
1. Separates the parietal pleura from the thoracic wall
2. Suprapleural membrane is thickening of the endothoracic fascia
a. Located lateral to the structures passing through the thoracic outlet
b. Membrane closes the thoracic outlet on either side of these structures
c. Attachments
i. Lateral: medial border of the 1st rib and costal cartilage
ii. Superior: transverse process of the 7th cervical vertebra
iii. Medial: fascia investing the structures passing from the thorax into the neck
d. Functions
i. Protects underlying cervical pleura
ii. Resists changes to the intrathoracic pressure during respiration
F. Diaphragm
1. Muscular, tendinous septum separating the chest cavity from the abdominal cavity
2. Three parts
a. Sternal part
b. Costal part
c. Vertebral part
3.
5.