THORAX

THE THORACIC WALL

 THE THORACIC WALL
• The thorax (or chest) is the region of the body between the neck and the abdomen. It
is flattened in front and behind but rounded at the sides.
• thoracic cage: The framework of the walls of the thorax, is formed by the vertebral
column behind, the ribs and intercostal spaces on either side, and the sternum and
costal cartilages in front.
• Superiorly, the thorax communicates with the neck, and inferiorly it is separated
from the abdomen by the diaphragm.
• The thoracic cage protects the lungs and heart and affords attachment for the muscles
of the thorax, upper extremity, abdomen, and back.
The cavity of the thorax can be divided into
(1) a median partition, called the mediastinum
(2) laterally placed pleurae and lungs.
The lungs are covered by a thin membrane called the visceral pleura, which passes
from each lung at its root (i.e., where the main air passages and blood vessels enter) to
the inner surface of the chest wall, where it is called the parietal pleura.
In this manner, two membranous sacs called the pleural cavities are formed, one on
each side of the thorax, between the lungs and the thoracic walls.
Structure of the Thoracic Wall
• The thoracic wall is covered on the outside by skin and by muscles attaching the
shoulder girdle to the trunk. It is lined with parietal pleura.
• The thoracic wall is formed posteriorly by the thoracic part of the vertebral column;
anteriorly by the sternum and costal cartilages; laterally by the ribs and intercostal
spaces; superiorly by the suprapleural membrane; and inferiorly by the diaphragm,
which separates the thoracic cavity from the abdominal cavity.
Sternum
• The sternum lies in the midline of the anterior chest wall. It is a flat bone that can be
divided into three parts: manubrium sterni, body of the sternum, and xiphoid process.
• The manubrium is the upper part of the sternum. It articulates with the body of the
sternum at the manubriosternal joint, and it also articulates with the clavicles and with the
1st costal cartilage and the upper part of the 2nd costal cartilages on each side. It lies
opposite the 3rd and 4th thoracic vertebrae.
• The body of the sternum articulates above with the manubrium at the manubriosternal
joint and below with the xiphoid process at the xiphisternal joint. On each side, it
articulates with the 2nd to the 7th costal cartilages.
• .
• The xiphoid process is a thin plate of cartilage that becomes ossified at its proximal
end during adult life. No ribs or costal cartilages are attached to it.
• The sternal angle (angle of Louis), formed by the articulation of the manubrium
with the body of the sternum, can be recognized by the presence of a transverse ridge
on the anterior aspect of the sternum.
• The transverse ridge lies at the level of the 2nd costal cartilage, the point from which
all costal cartilages and ribs are counted.
• The sternal angle lies opposite the intervertebral disc between the 4th and 5th
thoracic vertebrae.
• The xiphisternal joint lies opposite the body of the ninth thoracic vertebra
 RIBS
• There are 12 pairs of ribs, all of which are attached posteriorly to the thoracic
vertebrae. The ribs are divided into three categories:
• True ribs: The upper seven pairs are attached anteriorly to the sternum by their costal
cartilages.
• False ribs: The 8th, 9th, and 10th pairs of ribs are attached anteriorly to each other
and to the 7th rib by means of their costal cartilages and small synovial joints.
• Floating ribs: The 11th and 12th pairs have no anterior attachment.
 typical rib
• A typical rib is a long, twisted, flat bone having a rounded, smooth superior border and a sharp, thin
inferior border. The inferior border overhangs and forms the costal groove, which accommodates the
intercostal vessels and nerve. The anterior end of each rib is attached to the corresponding costal
cartilage.
• A rib has a head, neck, tubercle, shaft, and angle.
• The head has two facets for articulation with the numerically corresponding vertebral body and
that of the vertebra immediately above.
• The neck is a constricted portion situated between the head and the tubercle.
• The tubercle is a prominence on the outer surface of the rib at the junction of the neck with the
shaft. It has a facet for articulation with the transverse process of the numerically corresponding
vertebra.
• The shaft is thin and flattened and twisted on its long axis. Its inferior border has the costal groove.
The angle is where the shaft of the rib bends sharply forward.
 atypical rib

• The 1st rib is important clinically because of its close relationship to the lower nerves of
the brachial plexus and the main vessels to the arm, namely, the subclavian artery and vein.
• This rib is small and flattened from above downward. The scalenus anterior muscle is
attached to its upper surface and inner border.
• Anterior to the scalenus anterior, the subclavian vein crosses the rib; posterior to the
muscle attachment, the subclavian artery and the lower trunk of the brachial plexus cross
the rib and lie in contact with the bone.
 COSTAL CARTILAGES
• Costal cartilages are bars of cartilage connecting the upper seven ribs to the lateral
edge of the sternum and the 8th, 9th, and 10th ribs to the cartilage immediately above.
• The cartilages of the 11th and 12th ribs end in the abdominal musculature.
• The costal cartilages contribute significantly to the elasticity and mobility of the
thoracic walls.
• In old age, the costal cartilages tend to lose some of their flexibility as the result of
superficial calcification.
 JOINTS OF THE CHEST WALL
• Joints of the Sternum
• The manubriosternal joint is a cartilaginous joint between the manubrium and the
body of the sternum. A small amount of angular movement is possible during
respiration.
• The xiphisternal joint is a cartilaginous joint between the xiphoid process
(cartilage) and the body of the sternum. The xiphoid process usually fuses with the
body of the sternum during middle age.
 JOINTS OF THE RIBS

• Joints of the Heads of the Ribs

• The 1st rib and the three lowest ribs have a single synovial joint with their
corresponding vertebral body. For the 2nd to 9th ribs, the head articulates by means of a
synovial joint with the corresponding vertebral body and that of the vertebra above it.
There is a strong intraarticular ligament that connects the head to the intervertebral
disc.
• Joints of the Tubercles of the Ribs
• The tubercle of a rib articulates by means of a synovial joint with the transverse
process of the corresponding vertebra. (This joint is absent on the 11th and 12th ribs.)
• Joints of the Ribs and Costal Cartilages
These joints are cartilaginous joints. No movement is possible.
• Joints of the Costal Cartilages with the Sternum
The 1st costal cartilages articulate with the manubrium, by cartilaginous joints that permit
no movement. The 2nd to 7th costal cartilages articulate with the lateral border of the
sternum by synovial joints. In addition, the 6th, 7th, 8th, 9th, and 10th costal cartilages
articulate with one another along their borders by small synovial joints. The cartilages of
the 11th and 12th ribs are embedded in the abdominal musculature.
• Movements of the Ribs and Costal Cartilages
The 1st ribs and their costal cartilages are fixed to the manubrium and are immobile. The
raising and lowering of the ribs during respiration are accompanied by movements in both
the joints of the head and the tubercle, permitting the neck of each rib to rotate around its
own axis.