Muhammad Sohaib Shahid (Lecturer & Course Co-ordinator BS-MIT) University Institute of Radiological Sciences & Medical Imaging Technology (UIRSMIT)

Muhammad Sohaib Shahid(Lecturer & Course Co-ordinator BS-MIT)

University Institute of Radiological Sciences & Medical Imaging

Technology (UIRSMIT)

The Thoracic Wall

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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.

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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 stern• Body of the sternum • 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 first costal cartilage and the upper part of the second costal cartilages on each side . It lies opposite the third and fourth 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 second to the seventh 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.

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• 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 second costal cartilage, the point from which all costal cartilages and ribs are counted. The sternal angle lies opposite the intervertebral disc between the fourth and fifth thoracic vertebrae.

• The xiphisternal joint lies opposite the body of the ninth thoracic vertebra

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Clinical Notes

Sternum and Marrow Biopsy• Since the sternum possesses red hematopoietic

marrow throughout life, it is a common site for marrow biopsy. Under a local anaesthetic, a wide-bore needle is introduced into the marrow cavity through the anterior surface of the bone.

• The sternum may also be split at operation to allow the surgeon to gain easy access to the heart, great vessels, and thymus.

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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.

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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 (Fig. 2-4). 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.

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Atypical Rib

• The first 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.

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Clinical Notes

Cervical Rib• A cervical rib (i.e., a rib arising from the anterior tubercle

of the transverse process of the seventh cervical vertebra) occurs in about 0.5% of humans . It may have a free anterior end, may be connected to the first rib by a fibrous band, or may articulate with the first rib.

• The importance of a cervical rib is that it can cause pressure on the lower trunk of the brachial plexus in some patients, producing pain down the medial side of the forearm and hand and wasting of the small muscles of the hand. It can also exert pressure on the overlying subclavian artery and interfere with the circulation of the upper limb..

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Rib Excision• Rib excision is commonly performed by

thoracic surgeons wishing to gain entrance to the thoracic cavity. A longitudinal incision is made through the periosteum on the outer surface of the rib and a segment of the rib is removed. A second longitudinal incision is then made through the bed of the rib, which is the inner covering of periosteum. After the operation, the rib regenerates from the osteogenetic layer of the periosteum.

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Rib Fractures

• Fractures of the ribs are common chest injuries.• In children, the ribs are highly elastic, and fractures in this age group

are therefore rare. Unfortunately, the pliable chest wall in the young can be easily compressed so that the underlying lungs and heart may be injured.

• With increasing age, the rib cage becomes more rigid, owing to the deposit of calcium in the costal cartilages, and the ribs become brittle. The ribs then tend to break at their weakest part, their angles.

• The ribs prone to fracture are those that are exposed or relatively fixed. Ribs 5 through 10 are the most commonly fractured ribs. The first four ribs are protected by the clavicle and pectoral muscles anteriorly and by the scapula and its associated muscles posteriorly.

• Because the rib is sandwiched between the skin externally and the delicate pleura internally, it is not surprising that the jagged ends of a fractured rib may penetrate the lungs and present as a pneumothorax.

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Rib Contusion• Bruising of a rib, secondary to trauma, is the most

common rib injury. In this painful condition, a small haemorrhage occurs beneath the periosteum.

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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.

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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 first rib and the three lowest ribs have a single synovial joint with

their corresponding vertebral body. For the second to the ninth 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

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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 first costal cartilages articulate with the manubrium, by

cartilaginous joints that permit no movement . The 2nd to the 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.

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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.

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Thoracic Outlet

• The chest cavity communicates with the root of the neck through an opening called the thoracic outlet. It is called an outlet because important vessels and nerves emerge from the thorax here to enter the neck and upper limbs.

• The opening is bounded posteriorly by the first thoracic vertebra, laterally by the medial borders of the first ribs and their costal cartilages, and anteriorly by the superior border of the manubrium sterni. The opening is obliquely placed facing upward and forward. Through this small opening pass the oesophagus and trachea and many vessels and nerves. Because of the obliquity of the opening, the apices of the lung and pleurae project upward into the neck.

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• The thoracic cavity communicates with the abdomen through a large opening. The opening is bounded posteriorly by the 12th thoracic vertebra, laterally by the curving costal margin, and anteriorly by the xiphisternal joint. Through this large opening, which is closed by the diaphragm, pass the oesophagus and many large vessels and nerves, all of which pierce the diaphragm.

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Clinical Notes

• The Thoracic Outlet Syndrome• The brachial plexus of nerves (C5, 6, 7, and 8 and T1)

and the subclavian artery and vein are closely related to the upper surface of the first rib and the clavicle as they enter the upper limb . It is here that the nerves or blood vessels may be compressed between the bones. Most of the symptoms are caused by pressure on the lower trunk of the plexus producing pain down the medial side of the forearm and hand and wasting of the small muscles of the hand. Pressure on the blood vessels may compromise the circulation of the upper limb.

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Intercostal Spaces

• The spaces between the ribs contain three muscles of respiration:

• The external intercostal• The internal intercostal• The innermost intercostal muscle.

The innermost intercostal muscle is lined internally by the endothoracic fascia, which is lined internally by the parietal pleura. The intercostal nerves and blood vessels run between the intermediate and deepest layers of muscles . They are arranged in the following order from above downward: intercostal vein, intercostal artery, and intercostal nerve (i.e., VAN).

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Intercostal Muscles

• The external intercostal muscle forms the most superficial layer. Its fibers are directed downward and forward from the inferior border of the rib above to the superior border of the rib below . The muscle extends forward to the costal cartilage where it is replaced by an aponeurosis, the anterior (external) intercostal membrane .

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• The internal intercostal muscle forms the intermediate layer. Its fibers are directed downward and backward from the subcostal groove of the rib above to the upper border of the rib below . The muscle extends backward from the sternum in front to the angles of the ribs behind, where the muscle is replaced by an aponeurosis, the posterior (internal) intercostal membrane

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• The innermost intercostal muscle forms the deepest layer and corresponds to the transversus abdominis muscle in the anterior abdominal wall. It is an incomplete muscle layer and crosses more than one intercostal space within the ribs. It is related internally to fascia (endothoracic fascia) and parietal pleura and externally to the intercostal nerves and vessels. The innermost intercostal muscle can be divided into three portions , which are more or less separate from one another.

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Action

• When the intercostal muscles contract, they all tend to pull the ribs nearer to one another. If the 1st rib is fixed by the contraction of the muscles in the root of the neck, namely, the scaleni muscles, the intercostal muscles raise the 2nd to the 12th ribs toward the first rib, as in inspiration. If, conversely, the 12th rib is fixed by the quadratus lumborum muscle and the oblique muscles of the abdomen, the 1st to the 11th ribs will be lowered by the contraction of the intercostal muscles, as in expiration.

• In addition, the tone of the intercostal muscles during the different phases of respiration serves to strengthen the tissues of the intercostal spaces, thus preventing the sucking in or the blowing out of the tissues with changes in intrathoracic pressure.

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Nerve Supply

• The intercostal muscles are supplied by the corresponding intercostal nerves.

• The intercostal nerves and blood vessels (the neurovascular bundle), as in the abdominal wall, run between the middle and innermost layers of muscles . They are arranged in the following order from above downward: intercostal vein, intercostal artery, and intercostal nerve (i.e., VAN).

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Suprapleural Membrane

• Superiorly, the thorax opens into the root of the neck by a narrow aperture, the thoracic outlet . The outlet transmits structures that pass between the thorax and the neck (oesophagus, trachea, blood vessels, etc.) and for the most part lie close to the midline.

• On either side of these structures the outlet is closed by a dense fascial layer called the suprapleural membrane .

• This tent-shaped fibrous sheet is attached laterally to the medial border of the first rib and costal cartilage. It is attached at its apex to the tip of the transverse process of the seventh cervical vertebra and medially to the fascia investing the structures passing from the thorax into the neck.

• It protects the underlying cervical pleura and resists the changes in intrathoracic pressure occurring during respiratory movements.

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Diaphragm

• The diaphragm is a thin muscular and tendinous septum that separates the chest cavity above from the abdominal cavity below . It is pierced by the structures that pass between the chest and the abdomen.

• The diaphragm is the most important muscle of respiration. It is dome shaped and consists of a peripheral muscular part, which arises from the margins of the thoracic opening, and a centrally placed tendon .

The origin of the diaphragm can be divided into three parts:• A sternal part arising from the posterior surface of the xiphoid

process .• A costal part arising from the deep surfaces of the lower six ribs

and their costal cartilages .• A vertebral part arising by vertical columns or crura and from

the arcuate ligaments

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• The right crus arises from the sides of the bodies of the first three lumbar vertebrae and the intervertebral discs.

• The left crus arises from the sides of the bodies of the first two lumbar vertebrae and the intervertebral disc . Lateral to the crura the diaphragm arises from the medial and lateral arcuate ligaments .

• The medial arcuate ligament extends from the side of the body of the second lumbar vertebra to the tip of the transverse process of the first lumbar vertebra.

• The lateral arcuate ligament extends from the tip of the transverse process of the first lumbar vertebra to the lower border of the 12th rib.

• The medial borders of the two crura are connected by a median arcuate ligament, which crosses over the anterior surface of the aorta

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• The diaphragm is inserted into a central tendon, which is shaped like three leaves.

• The superior surface of the tendon is partially fused with the inferior surface of the fibrous pericardium.

• Some of the muscle fibers of the right crus pass up to the left and surround the esophageal orifice in a sling like loop. These fibers appear to act as a sphincter and possibly assist in the prevention of regurgitation of the stomach contents into the thoracic part of the oesophagus

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Shape of the Diaphragm

• As seen from in front, the diaphragm curves up into right and left domes, or cupulae. The right dome reaches as high as the upper border of the fifth rib, and the left dome may reach the lower border of the fifth rib.

• (The right dome lies at a higher level, because of the large size of the right lobe of the liver.)

• The central tendon lies at the level of the xiphisternal joint. The domes support the right and left lungs, whereas the central tendon supports the heart.

• The levels of the diaphragm vary with the phase of respiration, the posture, and the degree of distention of the abdominal viscera. The diaphragm is lower when a person is sitting or standing; it is higher in the supine position and after a large meal.

• When seen from the side, the diaphragm has the appearance of an inverted J, the long limb extending up from the vertebral column and the short limb extending forward to the xiphoid process

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Openings in the Diaphragm

• The diaphragm has three main openings:• The aortic opening lies anterior to the body of the 12th

thoracic vertebra between the crura . It transmits the aorta, the thoracic duct, and the azygos vein.

• The esophageal opening lies at the level of the 10th thoracic vertebra in a sling of muscle fibers derived from the right crus . It transmits the oesophagus, the right and left vagus nerves, the esophageal branches of the left gastric vessels, and the lymphatics from the lower third of the oesophagus.

• The caval opening lies at the level of the eighth 8th thoracic vertebra in the central tendon . It transmits the inferior vena cava and terminal branches of the right phrenic nerve.

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Functions of the Diaphragm

• Muscle of inspiration: On contraction, the diaphragm pulls its central tendon down and increases the vertical diameter of the thorax. The diaphragm is the most important muscle used in inspiration.

• Muscle of abdominal straining: The contraction of the diaphragm assists the contraction of the muscles of the anterior abdominal wall in raising the intra-abdominal pressure for micturition, defecation, and parturition. This mechanism is further aided by the person taking a deep breath and closing the glottis of the larynx. The diaphragm is unable to rise because of the air trapped in the respiratory tract. Now and again, air is allowed to escape, producing a grunting sound.

• Weight-lifting muscle: In a person taking a deep breath and holding it (fixing the diaphragm), the diaphragm assists the muscles of the anterior abdominal wall in raising the intra-abdominal pressure to such an extent that it helps support the vertebral column and prevent flexion. This greatly assists the postvertebral muscles in the lifting of heavy weights. Needless to say, it is important to have adequate sphincteric control of the bladder and anal canal under these circumstances.

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• Thoracoabdominal pump: The descent of the diaphragm decreases the intrathoracic pressure and at the same time increases the intra-abdominal pressure. This pressure change compresses the blood in the inferior vena cava and forces it upward into the right atrium of the heart. Lymph within the abdominal lymph vessels is also compressed, and its passage upward within the thoracic duct is aided by the negative intrathoracic pressure. The presence of valves within the thoracic duct prevents backflow.

Action of the Diaphragm• On contraction, the diaphragm pulls down its central

tendon and increases the vertical diameter of the thorax.

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Nerve Supply of the Diaphragm

• Motor nerve supply: The right and left phrenic nerves (C3, 4, 5)

• Sensory nerve supply: The parietal pleura and peritoneum covering the central surfaces of the diaphragm are from the phrenic nerve and the periphery of the diaphragm is from the lower six intercostal nerves.

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Paralysis of the Diaphragm

• A single dome of the diaphragm may be paralyzed by crushing or sectioning of the phrenic nerve in the neck.

• This may be necessary in the treatment of certain forms of lung tuberculosis, when the physician wishes to rest the lower lobe of the lung on one side.

• Occasionally, the contribution from the fifth cervical spinal nerve joins the phrenic nerve late as a branch from the nerve to the subclavius muscle. This is known as the accessory phrenic nerve. To obtain complete paralysis under these circumstances, the nerve to the subclavius muscle must also be sectioned.

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Hiccup

• Hiccup is the involuntary spasmodic contraction of the diaphragm accompanied by the approximation of the vocal folds and closure of the glottis of the larynx.

• It is a common condition in normal individuals and occurs after eating or drinking as a result of gastric irritation of the vagus nerve endings.

• It may, however, be a symptom of disease such as pleurisy, peritonitis, pericarditis, or uraemia.

Thoracotomy• In patients with penetrating chest wounds with uncontrolled

intrathoracic haemorrhage, thoracotomy may be a life-saving procedure

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Internal Thoracic Artery

• The internal thoracic artery supplies the anterior wall of the body from the clavicle to the umbilicus. It is a branch of the first part of the subclavian artery in the neck. It descends vertically on the pleura behind the costal cartilages, a fingerbreadth lateral to the sternum, and ends in the sixth intercostal space by dividing into the superior epigastric and musculophrenic arteries .

• Branches• Two anterior intercostal arteries for the upper six intercostal spaces• Perforating arteries, which accompany the terminal branches of the

corresponding intercostal nerves• The pericardiacophrenic artery, which accompanies the phrenic nerve and

supplies the pericardium• Mediastinal arteries to the contents of the anterior mediastinum (e.g., the

thymus)• The superior epigastric artery, which enters the rectus sheath of the anterior

abdominal wall and supplies the rectus muscle as far as the umbilicus• The musculophrenic artery, which runs around the costal margin of the

diaphragm and supplies the lower intercostal spaces and the diaphragm

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Internal Thoracic Vein• The internal thoracic vein accompanies the internal

thoracic artery and drains into the brachiocephalic vein on each side.

Levatores Costarum• There are 12 pairs of muscles. Each levator costa is

triangular in shape and arises by its apex from the tip of the transverse process and is inserted into the rib below.

• Action: Each raises the rib below and is therefore an inspiratory muscle.

• Nerve supply: Posterior rami of thoracic spinal nerves

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• Serratus Posterior Superior Muscle• The serratus posterior superior is a thin, flat muscle that

arises from the lower cervical and upper thoracic spines. Its fibers pass downward and laterally and are inserted into the upper ribs.

• Action: It elevates the ribs and is therefore an inspiratory muscle.

• Nerve supply: Intercostal nerves• Serratus Posterior Inferior Muscle• The serratus posterior inferior is a thin, flat muscle that arises

from the upper lumbar and lower thoracic spines. Its fibers pass upward and laterally and are inserted into the lower ribs.

• Action: It depresses the ribs and is therefore an expiratory muscle.

• Nerve supply: Intercostal nerves

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Internal Thoracic Artery in the Treatment of Coronary Artery Disease

• In patients with occlusive coronary disease caused by atherosclerosis, the diseased arterial segment can be bypassed by inserting a graft. The graft most commonly used is the great saphenous vein of the leg .

• In some patients, the myocardium can be revascularize by surgically mobilizing one of the internal thoracic arteries and joining its distal cut end to a coronary artery.

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Radiographic Anatomy of Chest