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Chapter 2 The Thorax: Part I—The Thoracic Wall A 20-year-old woman was the innocent victim of a street shoot-out involving drugs. On examination, the patient showed signs of severe hemorrhage and was in a state of shock. Her pulse was rapid and her blood pressure was dangerously low. There was a small entrance wound about 1 cm across in the fourth left intercostal space about 3 cm from the lateral margin of the sternum. There was no exit wound. The left side of her chest was dull on percussion, and breath sounds were absent on that side of the chest. A chest tube was immediately introduced through the chest wall. Because of the massive amounts of blood pouring out of the tube, it was decided to enter the chest (thoracotomy). The physician carefully counted the ribs to find the fourth intercostal space and cut the layers of tissue to enter the pleural space (cavity). She was particularly careful to avoid important anatomic structures. The incision was made in the fourth left intercostal space along a line that extended from the lateral margin of the sternum to the anterior axillary line. The following structures were incised: skin, subcutaneous tissue, pectoral muscles and serratus anterior muscle, external intercostal muscle and anterior intercostal membrane, internal intercostal muscle, innermost intercostal muscle, endothoracic fascia, and parietal pleura. The internal thoracic artery, which descends just lateral to the sternum and the intercostal vessels and nerve, must be avoided as the knife cuts through the layers of tissue to enter the chest. The cause of the hemorrhage was perforation of the left atrium of the heart by the bullet. A physician must have a knowledge of chest wall anatomy to make a reasoned diagnosis and institute treatment. Chapter Objectives

  • An understanding of the structure of the chest wall and the diaphragm is essential if one is to understand the normal movements of the chest wall in the process of aeration of the lungs.
  • Contained within the protective thoracic cage are the important life-sustaining organs—lungs, heart, and major blood vessels. In addition, the lower part of the cage overlaps the upper abdominal organs, such as the liver, stomach, and spleen, and offers them considerable protection. Although the chest wall is strong, blunt or penetrating wounds can injure the soft organs beneath it. This is especially so in an era in which automobile accidents, stab wounds, and gunshot wounds are commonplace.
  • Because of the clinical importance of the chest wall, examiners tend to focus on this area. Questions concerning the ribs and their movements; the diaphragm, its attachments, and its function; and the contents of an intercostal space have been asked many times.

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Basic Anatomy 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. The framework of the walls of the thorax, which is referred to as the thoracic cage, 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 a median partition, called the mediastinum, and the 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 (Fig. 2-1); 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. P.47
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 (Fig. 2-1). 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 (Fig. 2-1). The xiphoid process (Fig. 2-1) 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 (Fig. 2-2). 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 (Fig. 2-2).

Figure 2-1 A. Anterior view of the sternum. B. Sternum, ribs, and costal cartilages forming the thoracic skeleton.

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 anesthetic, 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. Ribs There are 12 pairs of ribs, all of which are attached posteriorly to the thoracic vertebrae (Figs. 2-1, 2-3, 2-4, and 2-5). 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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Figure 2-2 Lateral view of the thorax showing the relationship of the surface markings to the vertebral levels.
Figure 2-3 Thoracic vertebra. A. Superior surface. B. Lateral surface.

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Figure 2-4 Fifth right rib as it articulates with the vertebral column posteriorly and the sternum anteriorly. Note that the rib head articulates with the vertebral body of its own number and that of the vertebra immediately above. Note also the presence of the costal groove along the inferior border of the rib.

Typical Rib A typical rib is a long, twisted, flat bone having a rounded, smooth superior border and a sharp, thin inferior border (Figs. 2-4 and 2-5). 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 (Fig. 2-4).

Figure 2-5 Fifth right rib, as seen from the posterior aspect.

A rib has a head, neck, tubercle, shaft, and angle (Figs. 2-4 and 2-5). The head has two facets for articulation with the numerically corresponding vertebral body and that of the vertebra immediately above (Fig. 2-4). The neck is a constricted portion situated between the head and the P.50
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.

Figure 2-6 Thoracic outlet showing the cervical dome of pleura on the left side of the body and its relationship to the inner border of the first rib. Note also the presence of brachial plexus and subclavian vessels. (Anatomists often refer to the thoracic outlet as the thoracic inlet.)

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 (Fig. 2-6). 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. 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 (Fig. 2-7). 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. 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. P.51
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 (Fig. 2-1). 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 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 (Fig. 2-4). 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 (Fig. 2-4). (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.

Figure 2-7 Thoracic outlet as seen from above. Note the presence of the cervical ribs (black) on both sides. On the right side of the thorax, the rib is almost complete and articulates anteriorly with the first rib. On the left side of the thorax, the rib is rudimentary but is continued forward as a fibrous band that is attached to the first costal cartilage. Note that the cervical rib may exert pressure on the lower trunk of the brachial plexus and may kink the subclavian artery.

Joints of the Costal Cartilages with the Sternum The first costal cartilages articulate with the manubrium, by cartilaginous joints that permit no movement (Fig. 2-1). 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. 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. Openings of the Thorax 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 esophagus 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. 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 esophagus and many large vessels and nerves, all of which pierce the diaphragm. 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 (see Fig. 2-6). 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. P.52
Intercostal Spaces The spaces between the ribs contain three muscles of respiration: the external intercostal, the internal intercostal, and 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 (Fig. 2-8). They are arranged in the following order from above downward: intercostal vein, intercostal artery, and intercostal nerve (i.e., VAN). 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 P.53
border of the rib below (Fig. 2-8). The muscle extends forward to the costal cartilage where it is replaced by an aponeurosis, the anterior (external) intercostal membrane (Fig. 2-9).

Figure 2-8 A. Section through an intercostal space. B. Structures penetrated by a needle when it passes from skin surface to pleural cavity. Depending on the site of penetration, the pectoral muscles will be pierced in addition to the serratus anterior muscle.
Figure 2-9 Cross section of the thorax showing distribution of a typical intercostal nerve and a posterior and an anterior intercostal artery.

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 (Fig. 2-8). 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 (Fig. 2-9). 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 (Fig. 2-9), which are more or less separate from one another. 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. For further details concerning the action of these muscles, see mechanics of respiration on page 100. 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 (Figs. 2-8 and 2-9). They are arranged in the following order from above downward: intercostal vein, intercostal artery, and intercostal nerve (i.e., VAN). Intercostal Arteries and Veins Each intercostal space contains a large single posterior intercostal artery and two small anterior intercostal arteries.

  • The posterior intercostal arteries of the first two spaces are branches from the superior intercostal artery, a branch of the costocervical trunk of the subclavian artery. The posterior intercostal arteries of the lower nine spaces are branches of the descending thoracic aorta (Figs. 2-9 and 2-10).
  • The anterior intercostal arteries of the first six spaces are branches of the internal thoracic artery (Figs. 2-9 and 2-10), which arises from the first part of the subclavian artery. The anterior intercostal arteries of the lower spaces are branches of the musculophrenic artery, one of the terminal branches of the internal thoracic artery.

Each intercostal artery gives off branches to the muscles, skin, and parietal pleura. In the region of the breast in the female, the branches to the superficial structures are particularly large. The corresponding posterior intercostal veins drain backward into the azygos or hemiazygos veins (Figs. 2-10 and 2-11), and the anterior intercostal veins drain forward into the internal thoracic and musculophrenic veins. P.54

Figure 2-10 A. Internal view of the posterior end of two typical intercostal spaces; the posterior intercostal membrane has been removed for clarity. B. Anterior view of the chest showing the courses of the internal thoracic vessels. These vessels descend about one fingerbreadth from the lateral margin of the sternum.

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Figure 2-11 The common arrangement of the azygos vein, the superior hemiazygos (accessory hemiazygos) vein, and the inferior hemiazygos (hemiazygos) vein.

Intercostal Nerves The intercostal nerves are the anterior rami of the first 11 thoracic spinal nerves (Fig. 2-12). The anterior ramus of the 12th thoracic nerve lies in the abdomen and runs forward in the abdominal wall as the subcostal nerve. Each intercostal nerve enters an intercostal space between the parietal pleura and the posterior intercostal membrane (Figs. 2-8 and 2-9). It then runs forward inferiorly to the intercostal vessels in the subcostal groove of the corresponding rib, between the innermost intercostal and internal intercostal muscle. The first six nerves are distributed within their intercostal spaces. The seventh to ninth intercostal nerves leave the anterior ends of their intercostal spaces by passing deep to the costal cartilages, to enter the anterior abdominal wall. The 10th and 11th nerves, since the corresponding ribs are floating, pass directly into the abdominal wall. Branches See Figures 2-9 and 2-12.

  • Rami communicantes connect the intercostal nerve to a ganglion of the sympathetic trunk (see Fig. 1-26). The gray ramus joins the nerve medial at the point at which the white ramus leaves it.
  • The collateral branch runs forward inferiorly to the main nerve on the upper border of the rib below.
  • The lateral cutaneous branch reaches the skin on the side of the chest. It divides into an anterior and a posterior branch.
  • The anterior cutaneous branch, which is the terminal portion of the main trunk, reaches the skin near the midline. It divides into a medial and a lateral branch.
  • Muscular branches run to the intercostal muscles.
  • Pleural sensory branches go to the parietal pleura.
  • Peritoneal sensory branches (7th to 11th intercostal nerves only) run to the parietal peritoneum.

Clinical Notes Skin Innervation of the Chest Wall and Referred Pain Above the level of the sternal angle, the cutaneous innervation of the anterior chest wall is derived from the supraclavicular nerves (C3 and 4). Below this level, the anterior and lateral cutaneous branches of the intercostal nerves supply oblique bands of skin in regular sequence. The skin on the posterior surface of the chest wall is supplied by the posterior rami of the spinal nerves. The arrangement of the dermatomes is shown in Figures 1-23 and 1-24. An intercostal nerve not only supplies areas of skin, but also supplies the ribs, costal cartilages, intercostal muscles, and parietal pleura lining the intercostal space. Furthermore, the 7th to 11th intercostal nerves leave the thoracic wall and enter the anterior abdominal wall so that they, in addition, supply dermatomes on the anterior abdominal wall, muscles of the anterior abdominal wall, and parietal peritoneum. This latter fact is of great clinical importance because it means that disease in the thoracic wall may be revealed as pain in a dermatome that extends across the costal margin into the anterior abdominal wall. For example, a pulmonary thromboembolism or a pneumonia with pleurisy involving the costal parietal pleura could give rise to abdominal pain and tenderness and rigidity of the abdominal musculature. The abdominal pain in these instances is called referred pain. Herpes Zoster Herpes zoster, or shingles, is a relatively common condition caused by the reactivation of the latent varicella-zoster virus in a patient who has previously had chickenpox. The lesion is seen as an inflammation and degeneration of the sensory neuron in a cranial or spinal nerve with the formation of vesicles with inflammation of the skin. In the thorax the first symptom is a band of dermatomal pain in the distribution of the sensory neuron in a thoracic spinal nerve, followed in a few days by a skin eruption. The condition occurs most frequently in patients older than 50 years. The first intercostal nerve is joined to the brachial plexus by a large branch that is equivalent to the lateral cutaneous branch of typical intercostal nerves. The remainder of the first intercostal nerve is small, and there is no anterior cutaneous branch. The second intercostal nerve is joined to the medial cutaneous nerve of the arm by a branch called the intercostobrachial nerve, which is equivalent to the P.56
lateral cutaneous branch of other nerves. The second intercostal nerve therefore supplies the skin of the armpit and the upper medial side of the arm. In coronary artery disease, pain is referred along this nerve to the medial side of the arm.

Figure 2-12 The distribution of two intercostal nerves relative to the rib cage.

Clinical Notes Intercostal Nerve Block Area of Anesthesia The skin and the parietal pleura cover the outer and inner surfaces of each intercostal space, respectively; the 7th to 11th intercostal nerves supply the skin and the parietal peritoneum covering the outer and inner surfaces of the abdominal wall, respectively. Therefore, an intercostal nerve block will also anesthetize these areas. In addition, the periosteum of the adjacent ribs is anesthetized. Indications Intercostal nerve block is indicated for repair of lacerations of the thoracic and abdominal walls, for relief of pain in rib fractures, and to allow pain-free respiratory movements. Procedure To produce analgesia of the anterior and lateral thoracic and abdominal walls, the intercostal nerve should be blocked before the lateral cutaneous branch arises at the midaxillary line. The ribs may be identified by counting down from the 2nd (opposite sternal angle) or up from the 12th. The needle is directed toward the rib near the lower border (Fig. 2-8), and the tip comes to rest near the subcostal groove, where the local anesthetic is infiltrated around the nerve. Remember that the order of structures lying in the neurovascular bundle from above downward is intercostal vein, artery, and nerve and that these structures are situated between the posterior intercostal membrane of the internal intercostal muscle and the parietal pleura. Furthermore, laterally the nerve lies between the internal intercostal muscle and the innermost intercostal muscle. Anatomy of Complications Complications include pneumothorax and hemorrhage. Pneumothorax can occur if the needle point misses the subcostal groove and penetrates too deeply through the parietal pleura. Hemorrhage is caused by the puncture of the intercostal blood vessels. This is a common complication, so aspiration should always be performed before injecting the anesthetic. A small hematoma may result. P.57
With the exceptions noted, the first six intercostal nerves therefore supply the skin and the parietal pleura covering the outer and inner surfaces of each intercostal space, respectively, and the intercostal muscles of each intercostal space and the levatores costarum and serratus posterior muscles. In addition, the 7th to the 11th intercostal nerves supply the skin and the parietal peritoneum covering the outer and inner surfaces of the abdominal wall, respectively, and the anterior abdominal muscles, which include the external oblique, internal oblique, transversus abdominis, and rectus abdominis muscles. Suprapleural Membrane Superiorly, the thorax opens into the root of the neck by a narrow aperture, the thoracic outlet (see page 51). The outlet transmits structures that pass between the thorax and the neck (esophagus, 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 (Fig. 2-13). 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. Endothoracic Fascia The endothoracic fascia is a thin layer of loose connective tissue that separates the parietal pleura from the thoracic wall. The suprapleural membrane is a thickening of this fascia. Diaphragm The diaphragm is a thin muscular and tendinous septum that separates the chest cavity above from the abdominal cavity below (Fig. 2-16). 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 (Fig. 2-16). The origin of the diaphragm can be divided into three parts:

  • A sternal part arising from the posterior surface of the xiphoid process (Fig. 2-2)
  • A costal part arising from the deep surfaces of the lower six ribs and their costal cartilages (Fig. 2-16)
  • A vertebral part arising by vertical columns or crura and from the arcuate ligaments

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 (Fig. 2-16). Lateral to the crura the diaphragm arises from the medial and lateral arcuate ligaments (Fig. 2-16). 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 (Fig. 2-16).

Figure 2-13 Lateral view of the upper opening of the thoracic cage showing how the apex of the lung projects superiorly into the root of the neck. The apex of the lung is covered with visceral and parietal layers of pleura and is protected by the suprapleural membrane, which is a thickening of the endothoracic fascia.

Clinical Notes Thoracic Cage Distortion The shape of the thorax can be distorted by congenital anomalies of the vertebral column or by the ribs. Destructive disease of the vertebral column that produces lateral flexion or scoliosis results in marked distortion of the thoracic cage. Clinical Notes Traumatic Injury to the Thorax Traumatic injury to the thorax is common, especially as a result of automobile accidents. Fractured Sternum The sternum is a resilient structure that is held in position by relatively pliable costal cartilages and bendable ribs. For these reasons, fracture of the sternum is not common; however, it does occur in high-speed motor vehicle accidents. Remember that the heart lies posterior to the sternum and may be severely contused by the sternum on impact. Rib Contusion Bruising of a rib, secondary to trauma, is the most common rib injury. In this painful condition, a small hemorrhage occurs beneath the periosteum. 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. The 11th and 12th ribs float and move with the force of impact. 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. Severe localized pain is usually the most important symptom of a fractured rib. The periosteum of each rib is innervated by the intercostal nerves above and below the rib. To encourage the patient to breathe adequately, it may be necessary to relieve the pain by performing an intercostal nerve block. Flail Chest In severe crush injuries, a number of ribs may break. If limited to one side, the fractures may occur near the rib angles and anteriorly near the costochondral junctions. This causes flail chest, in which a section of the chest wall is disconnected to the rest of the thoracic wall. If the fractures occur on either side of the sternum, the sternum may be flail. In either case, the stability of the chest wall is lost, and the flail segment is sucked in during inspiration and driven out during expiration, producing paradoxical and ineffective respiratory movements. Traumatic Injury to the Back of the Chest The posterior wall of the chest in the midline is formed by the vertebral column. In severe posterior chest injuries the possibility of a vertebral fracture with associated injury to the spinal cord should be considered. Remember also the presence of the scapula, which overlies the upper seven ribs. This bone is covered with muscles and is fractured only in cases of severe trauma. Traumatic Injury to the Abdominal Viscera and the Chest When the anatomy of the thorax is reviewed, it is important to remember that the upper abdominal organs—namely, the liver, stomach, and spleen—may be injured by trauma to the rib cage. In fact, any injury to the chest below the level of the nipple line may involve abdominal organs as well as chest organs. P.58
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 slinglike 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 esophagus (Fig. 2-16). 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 (Fig. 2-2). 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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Figure 2-14 Tube thoracostomy. A. The site for insertion of the tube at the anterior axillary line. The skin incision is usually made over the intercostal space one below the space to be pierced. B. The various layers of tissue penetrated by the scalpel and later the tube as they pass through the chest wall to enter the pleural cavity (space). The incision through the intercostal space is kept close to the upper border of the rib to avoid injuring the intercostal vessels and nerve. C. The tube advancing superiorly and posteriorly in the pleural space.

Action of the Diaphragm On contraction, the diaphragm pulls down its central tendon and increases the vertical diameter of the thorax. 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.
  • 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 P.60
    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.

Clinical Notes Needle Thoracostomy A needle thoracostomy is necessary in patients with tension pneumothorax (air in the pleural cavity under pressure) or to drain fluid (blood or pus) away from the pleural cavity to allow the lung to re-expand. It may also be necessary to withdraw a sample of pleural fluid for microbiologic examination. Anterior Approach For the anterior approach, the patient is in the supine position. The sternal angle is identified, and then the second costal cartilage, the second rib, and the second intercostal space are found in the midclavicular line. Lateral Approach For the lateral approach, the patient is lying on the lateral side. The second intercostal space is identified as above, but the anterior axillary line is used. The skin is prepared in the usual way, and a local anesthetic is introduced along the course of the needle above the upper border of the third rib. The thoracostomy needle will pierce the following structures as it passes through the chest wall (Fig. 2-8): (a) skin, (b) superficial fascia (in the anterior approach the pectoral muscles are then penetrated), (c) serratus anterior muscle, (d) external intercostal muscle, (e) internal intercostal muscle, (f) innermost intercostal muscle, (g) endothoracic fascia, and (h) parietal pleura. The needle should be kept close to the upper border of the third rib to avoid injuring the intercostal vessels and nerve in the subcostal groove. Tube Thoracostomy The preferred insertion site for a tube thoracostomy is the fourth or fifth intercostal space at the anterior axillary line (Fig. 2-14). The tube is introduced through a small incision. The neurovascular bundle changes its relationship to the ribs as it passes forward in the intercostal space. In the most posterior part of the space, the bundle lies in the middle of the intercostal space. As the bundle passes forward to the rib angle, it becomes closely related to the lower border of the rib above and maintains that position as it courses forward. The introduction of a thoracostomy tube or needle through the lower intercostal spaces is possible provided that the presence of the domes of the diaphragm is remembered as they curve upward into the rib cage as far as the fifth rib (higher on the right). Avoid damaging the diaphragm and entering the peritoneal cavity and injuring the liver, spleen, or stomach. Thoracotomy In patients with penetrating chest wounds with uncontrolled intrathoracic hemorrhage, thoracotomy may be a life-saving procedure. After preparing the skin in the usual way, the physician makes an incision over the fourth or fifth intercostal space, extending from the lateral margin of the sternum to the anterior axillary line (Fig. 2-15). Whether to make a right or left incision depends on the site of the injury. For access to the heart and aorta, the chest should be entered from the left side. The following tissues will be incised (Fig. 2-14): (a) skin, (b) subcutaneous tissue, (c) serratus anterior and pectoral muscles, (d) external intercostal muscle and anterior intercostal membrane, (e) internal intercostal muscle, (f) innermost intercostal muscle, (g) endothoracic fascia, and (h) parietal pleura. Avoid the internal thoracic artery, which runs vertically downward behind the costal cartilages about a fingerbreadth lateral to the margin of the sternum, and the intercostal vessels and nerve, which extend forward in the subcostal groove in the upper part of the intercostal space (Fig. 2-14). 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 uremia. 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. Penetrating Injuries of the Diaphragm Penetrating injuries can result from stab or bullet wounds to the chest or abdomen. Any penetrating wound to the chest below the level of the nipples should be suspected of causing damage to the diaphragm until proved otherwise. The arching domes of the diaphragm can reach the level of the fifth rib (the right dome can reach a higher level). 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 (Fig. 2-16). 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 (Fig. 2-16). It transmits the esophagus, the right and left vagus nerves, the esophageal branches of the left gastric vessels, and the lymphatics from the lower third of the esophagus.
  • The caval opening lies at the level of the eighth thoracic vertebra in the central tendon (Fig. 2-16). It transmits the inferior vena cava and terminal branches of the right phrenic nerve.

In addition to these openings, the sympathetic splanchnic nerves pierce the crura; the sympathetic trunks pass posterior to the medial arcuate ligament on each side; and the superior epigastric vessels pass between the sternal and costal origins of the diaphragm on each side (Fig. 2-16). P.61

Figure 2-15 Left thoracotomy. A. Site of skin incision over fourth or fifth intercostal space. B. The exposed ribs and associated muscles. The line of incision through the intercostal space should be placed close to the upper border of the rib to avoid injuring the intercostal vessels and nerve. C. The pleural space opened and the left side of the mediastinum exposed. The left phrenic nerve descends over the pericardium beneath the mediastinal pleura. The collapsed left lung must be pushed out of the way to visualize the mediastinum.

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Figure 2-16 Diaphragm as seen from below. The anterior portion of the right side has been removed. Note the sternal, costal, and vertebral origins of the muscle and the important structures that pass through it.

Embryologic Notes Development of the Diaphragm The diaphragm is formed from the following structures: (a) the septum transversum, which forms the muscle and central tendon; (b) the two pleuroperitoneal membranes, which are largely responsible for the peripheral areas of the diaphragmatic pleura and peritoneum that cover its upper and lower surfaces, respectively; and (c) the dorsal mesentery of the esophagus, in which the crura develop. The septum transversum is a mass of mesoderm that is formed in the neck by the fusion of the myotomes of the third, fourth, and fifth cervical segments. With the descent of the heart from the neck to the thorax, the septum is pushed caudally, pulling its nerve supply with it; thus, its motor nerve supply is derived from the third, fourth, and fifth cervical nerves, which are contained within the phrenic nerve. The pleuroperitoneal membranes grow medially from the body wall on each side until they fuse with the septum transversum anterior to the esophagus and with the dorsal mesentery posterior to the esophagus. During the process of fusion, the mesoderm of the septum transversum extends into the other parts, forming all the muscles of the diaphragm. The motor nerve supply to the entire muscle of the diaphragm is the phrenic nerve. The central pleura on the upper surface of the diaphragm and the peritoneum on the lower surface are also formed from the septum transversum, which explains their sensory innervation from the phrenic nerve. The sensory innervation of the peripheral parts of the pleura and peritoneum covering the peripheral areas of the upper and lower surfaces of the diaphragm is from the lower six thoracic nerves. This is understandable, since the peripheral pleura and peritoneum from the pleuroperitoneal membranes are derived from the body wall. Diaphragmatic Herniae Congenital herniae occur as the result of incomplete fusion of the septum transversum, the dorsal mesentery, and the pleuroperitoneal membranes from the body wall. The herniae occur at the following sites: (a) the pleuroperitoneal canal (more common on the left side; caused by failure of fusion of the septum transversum with the pleuroperitoneal membrane), (b) the opening between the xiphoid and costal origins of the diaphragm, and (c) the esophageal hiatus. Acquired herniae may occur in middle-aged people with weak musculature around the esophageal opening in the diaphragm. These herniae may be either sliding or paraesophageal (Fig. 2-17). P.63

Figure 2-17 A. Sliding esophageal hernia. B. Paraesophageal hernia.

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 (Figs. 2-9 and 2-10). 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

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

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

A summary of the muscles of the thorax, their nerve supply, and their actions is given in Table 2-1. Radiographic Anatomy This is fully described on page 131. Clinical Notes 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 (see page 572). In some patients, the myocardium can be revascularized by surgically mobilizing one of the internal thoracic arteries and joining its distal cut end to a coronary artery. Lymph Drainage of the Thoracic Wall The lymph drainage of the skin of the anterior chest wall passes to the anterior axillary lymph nodes; that from the posterior chest wall passes to the posterior axillary nodes (Fig. 2-18). The lymph drainage of the intercostal spaces passes forward to the internal thoracic nodes, situated along the internal thoracic artery, and posteriorly to the posterior intercostal nodes and the para-aortic nodes in the posterior mediastinum. The lymphatic drainage of the breast is described on page 427. P.64
Surface Anatomy Anterior Chest Wall The suprasternal notch is the superior margin of the manubrium sterni and is easily felt between the prominent medial ends of the clavicles in the midline (Figs. 2-19 and 2-20). It lies opposite the lower border of the body of the second thoracic vertebra (Fig. 2-2). The sternal angle (angle of Louis) is the angle made between the manubrium and body of the sternum (Figs. 2-19 and 2-20). It lies opposite the intervertebral disc between the fourth and fifth thoracic vertebrae (Fig. 2-2). The position of the sternal angle can easily be felt and is often seen as a transverse ridge. The finger moved to the right or to the left will pass directly onto the second costal cartilage and then the second rib. All ribs may be counted from this point. Occasionally in a very muscular male, the ribs and intercostal spaces are often obscured by large pectoral muscles. In these cases, it may be easier to count up from the 12th rib.

Figure 2-18 Lymph drainage of the skin of the thorax and abdomen. Note that levels of the umbilicus anteriorly and iliac crests posteriorly may be regarded as watersheds for lymph flow.

The xiphisternal joint is the joint between the xiphoid process of the sternum and the body of the sternum (Fig. 2-21). It lies opposite the body of the ninth thoracic vertebra (Fig. 2-2). The subcostal angle is situated at the inferior end of the sternum, between the sternal attachments of the seventh costal cartilages (Fig. 2-21). The costal margin is the lower boundary of the thorax and is formed by the cartilages of the 7th, 8th, 9th, and 10th ribs and the ends of the 11th and 12th cartilages (Figs. 2-19 and 2-20). The lowest part of the costal margin is formed by the 10th rib and lies at the level of the third lumbar vertebra. P.65

Table 2-1 Muscles of the Thorax
Name of Muscle Origin Insertion Nerve Supply Action
External intercostal muscle (11) (fibers pass downward and forward) Inferior border of rib Superior border of rib below Intercostal nerves With first rib fixed, they raise ribs during inspiration and thus increase anteroposterior and transverse diameters of thorax
Internal intercostal muscle (11) (fibers pass downward and backward) Inferior border of rib Superior border of rib below Intercostal nerves With last rib fixed by abdominal muscles, they lower ribs during expiration
Innermost intercostal muscle (incomplete layer) Adjacent ribs Adjacent ribs Intercostal nerves Assists external and internal intercostal muscles
Diaphragm (most important muscle of respiration) Xiphoid process; lower six costal cartilages, first three lumbar vertebrae Central tendon Phrenic nerve Very important muscle of inspiration; increases vertical diameter of thorax by pulling central tendon downward; assists in raising lower ribs
Also used in abdominal straining and weight lifting
Levatores costarum (12) Tip of transverse process of C7 and T1–11 vertebrae Rib below Posterior rami of thoracic spinal nerves Raises ribs and therefore inspiratory muscles
Serratus posterior superior Lower cervical and upper thoracic spines Upper ribs Intercostal nerves Raises ribs and therefore inspiratory muscles
Serratus posterior inferior Upper lumbar and lower thoracic spines Lower ribs Intercostal nerves Depresses ribs and therefore expiratory muscles

Clinical Notes Anatomic and Physiologic Changes in the Thorax with Aging Certain anatomic and physiologic changes take place in the thorax with advancing years:

  • The rib cage becomes more rigid and loses its elasticity as the result of calcification and even ossification of the costal cartilages; this also alters their usual radiographic appearance.
  • The stooped posture (kyphosis), so often seen in the old because of degeneration of the intervertebral discs, decreases the chest capacity.
  • Disuse atrophy of the thoracic and abdominal muscles can result in poor respiratory movements.
  • Degeneration of the elastic tissue in the lungs and bronchi results in impairment of the movement of expiration.

These changes, when severe, diminish the efficiency of respiratory movements and impair the ability of the individual to withstand respiratory disease. The clavicle is subcutaneous throughout its entire length and can be easily palpated (Figs. 2-19 and 2-20). It articulates at its lateral extremity with the acromion process of the scapula. Ribs The first rib lies deep to the clavicle and cannot be palpated. The lateral surfaces of the remaining ribs can be felt by pressing the fingers upward into the axilla and drawing them downward over the lateral surface of the chest wall. The 12th rib can be used to identify a particular rib by counting from below. However, in some individuals, the 12th rib is very short and difficult to feel. For this reason, an alternative method may be used to identify ribs by first palpating the sternal angle and the second costal cartilage. Diaphragm The central tendon of the diaphragm lies directly behind the xiphisternal joint. In the midrespiratory position the summit of the right dome of the diaphragm arches upward as far as the upper border of the fifth rib in the midclavicular line, but the left dome only reaches as far as the lower border of the fifth rib. P.66

Figure 2-19 Anterior view of the thorax of a 27-year-old man.

Nipple In the male, the nipple usually lies in the fourth intercostal space about 4 in. (10 cm) from the midline. In the female, its position is not constant. Apex Beat of the Heart The apex of the heart is formed by the lower portion of the left ventricle. The apex beat is caused by the apex of the heart being thrust forward against the thoracic wall as the heart contracts. (The heart is thrust forward with each ventricular contraction because of the ejection of blood from the left ventricle into the aorta; the force of the blood in the aorta tends to cause the curved aorta to straighten slightly, thus pushing the heart forward.) The apex beat can usually be felt by placing the flat of the hand on the chest wall over the heart. After the area of cardiac pulsation has been determined, the apex beat is accurately localized by placing two fingers over the intercostal spaces and moving them until the point of maximum pulsation is found. The apex beat is normally found in the fifth left intercostal space 3.5 in. (9 cm) from the midline. Should you have difficulty in finding the apex beat, have the patient lean forward in the sitting position. In a female with pendulous breasts, the examining fingers should gently raise the left breast from below as the intercostal spaces are palpated. Axillary Folds The anterior fold is formed by the lower border of the pectoralis major muscle (Figs. 2-19 and 2-20). This can be made to stand out by asking the patient to press a hand hard against the hip. The posterior fold is formed by the tendon of the latissimus dorsi muscle as it passes around the lower border of the teres major muscle. Posterior Chest Wall The spinous processes of the thoracic vertebrae can be palpated in the midline posteriorly (Fig. 2-22). The index finger should be placed on the skin in the midline on the posterior surface of the neck and drawn downward in the nuchal groove. The first spinous process to be felt is that of the seventh cervical vertebrae (vertebra prominens). Below this level are the overlapping spines of the thoracic vertebrae. The spines of C1 to 6 vertebrae are covered by a large ligament, the ligamentum nuchae. It should be noted that the tip of a spinous process of a thoracic vertebra lies posterior to the body of the next vertebra below. The scapula (shoulder blade) is flat and triangular in shape and is located on the upper part of the posterior surface of the thorax. The superior angle lies opposite the spine of the second thoracic vertebra (Figs. 2-20 and 2-22). The spine of the scapula is subcutaneous, and the root of the spine lies on a level with the spine of the third thoracic vertebra (Figs. 2-21 and 2-22). The inferior angle lies on a level with the spine of the seventh thoracic vertebra (Figs. 2-20 and 2-22). P.67

Figure 2-20 A. Anterior view of the thorax and abdomen of a 29-year-old woman. B. Posterior view of the thorax of a 29-year-old woman.

Clinical Notes Clinical Examination of the Chest As medical personnel, you will be examining the chest to detect evidence of disease. Your examination consists of inspection, palpation, percussion, and auscultation. Inspection shows the configuration of the chest, the range of respiratory movement, and any inequalities on the two sides. The type and rate of respiration are also noted. Palpation enables the physician to confirm the impressions gained by inspection, especially of the respiratory movements of the chest wall. Abnormal protuberances or recession of part of the chest wall is noted. Abnormal pulsations are felt and tender areas detected. Percussion is a sharp tapping of the chest wall with the fingers. This produces vibrations that extend through the tissues of the thorax. Air-containing organs such as the lungs produce a resonant note; conversely, a more solid viscus such as the heart produces a dull note. With practice, it is possible to distinguish the lungs from the heart or liver by percussion. Auscultation enables the physician to listen to the breath sounds as the air enters and leaves the respiratory passages. Should the alveoli or bronchi be diseased and filled with fluid, the nature of the breath sounds will be altered. The rate and rhythm of the heart can be confirmed by auscultation, and the various sounds produced by the heart and its valves during the different phases of the cardiac cycle can be heard. It may be possible to detect friction sounds produced by the rubbing together of diseased layers of pleura or pericardium. To make these examinations, the physician must be familiar with the normal structure of the thorax and must have a mental image of the normal position of the lungs and heart in relation to identifiable surface landmarks. Furthermore, it is essential that the physician be able to relate any abnormal findings to easily identifiable bony landmarks so that he or she can accurately record and communicate them to colleagues. Since the thoracic wall actively participates in the movements of respiration, many bony landmarks change their levels with each phase of respiration. In practice, to simplify matters, the levels given are those usually found at about midway between full inspiration and full expiration. P.68
Lines of Orientation Several imaginary lines are sometimes used to describe surface locations on the anterior and posterior chest walls.

  • Midsternal line: Lies in the median plane over the sternum (Fig. 2-21)
  • Midclavicular line: Runs vertically downward from the midpoint of the clavicle (Fig. 2-21)
  • Anterior axillary line: Runs vertically downward from the anterior axillary fold (Fig. 2-21)
  • Posterior axillary line: Runs vertically downward from the posterior axillary fold
  • Midaxillary line: Runs vertically downward from a point situated midway between the anterior and posterior axillary folds
  • Scapular line: Runs vertically downward on the posterior wall of the thorax (Fig. 2-22), passing through the inferior angle of the scapula (arms at the sides)

Clinical Notes Rib and Costal Cartilage Identification When one is examining the chest from in front, the sternal angle is an important landmark. Its position can easily be felt and often be seen by the presence of a transverse ridge. The finger moved to the right or to the left passes directly onto the second costal cartilage and then the second rib. All other ribs can be counted from this point. The 12th rib can usually be felt from behind, but in some obese persons this may prove difficult. Trachea The trachea extends from the lower border of the cricoid cartilage (opposite the body of the sixth cervical vertebra) in the neck to the level of the sternal angle in the thorax (Fig. 2-23). It commences in the midline and ends just to the right of the midline by dividing into the right and left principal bronchi. At the root of the neck it may be palpated in the midline in the suprasternal notch. Lungs The apex of the lung projects into the neck. It can be mapped out on the anterior surface of the body by drawing a curved line, convex upward, from the sternoclavicular joint to a point 1 in. (2.5 cm) above the junction of the medial and intermediate thirds of the clavicle (Fig. 2-23). The anterior border of the right lung begins behind the sternoclavicular joint and runs downward, almost reaching the midline behind the sternal angle. It then continues downward until it reaches the xiphisternal joint (Fig. 2-23). The anterior border of the left lung has a similar course, but at the level of the fourth costal cartilage it deviates laterally and extends for a variable distance beyond the lateral margin of the sternum to form the cardiac notch (Fig. 2-23). This notch is produced by the heart displacing the lung to the left. The anterior border then turns sharply downward to the level of the xiphisternal joint. The lower border of the lung in midinspiration follows a curving line, which crosses the 6th rib in the midclavicular line and the 8th rib in the midaxillary line, and reaches the 10th rib adjacent to the vertebral column posteriorly (Figs. 2-23, 2-24, and 2-25). It is important to understand that the level of the inferior border of the lung changes during inspiration and expiration. The posterior border of the lung extends downward from the spinous process of the 7th cervical vertebra to the level of the 10th thoracic vertebra and lies about 1.5 in. (4 cm) from the midline (Fig. 2-24). The oblique fissure of the lung can be indicated on the surface by a line drawn from the root of the spine of the scapula obliquely downward, laterally and anteriorly, following the course of the sixth rib to the sixth costochondral junction. In the left lung the upper lobe lies above and anterior to this line; the lower lobe lies below and posterior to it (Figs. 2-23 and 2-24). In the right lung is an additional fissure, the horizontal fissure, which may be represented by a line drawn P.69
horizontally along the fourth costal cartilage to meet the oblique fissure in the midaxillary line (Figs. 2-23 and 2-25). Above the horizontal fissure lies the upper lobe and below it lies the middle lobe; below and posterior to the oblique fissure lies the lower lobe.

Figure 2-21 Surface landmarks of anterior (A) and posterior (B) thoracic walls.

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Figure 2-22 Surface landmarks of the posterior thoracic wall.
Figure 2-23 Surface markings of lungs and parietal pleura on the anterior thoracic wall.

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Figure 2-24 Surface markings of the lungs and parietal pleura on the posterior thoracic wall.
Figure 2-25 Surface markings of the lungs and parietal pleura on the lateral thoracic walls.

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Pleura The boundaries of the pleural sac can be marked out as lines on the surface of the body. The lines, which indicate the limits of the parietal pleura where it lies close to the body surface, are referred to as the lines of pleural reflection. The cervical pleura bulges upward into the neck and has a surface marking identical to that of the apex of the lung. A curved line may be drawn, convex upward, from the sternoclavicular joint to a point 1 in. (2.5 cm) above the junction of the medial and intermediate thirds of the clavicle (Fig. 2-23). The anterior border of the right pleura runs down behind the sternoclavicular joint, almost reaching the midline behind the sternal angle. It then continues downward until it reaches the xiphisternal joint. The anterior border of the left pleura has a similar course, but at the level of the fourth costal cartilage it deviates laterally and extends to the lateral margin of the sternum to form the cardiac notch. (Note that the pleural cardiac notch is not as large as the cardiac notch of the lung.) It then turns sharply downward to the xiphisternal joint (Fig. 2-23). The lower border of the pleura on both sides follows a curved line, which crosses the 8th rib in the midclavicular line and the 10th rib in the midaxillary line, and reaches the 12th rib adjacent to the vertebral column—that is, at the lateral border of the erector spinae muscle (Figs. 2-23, 2-24, and 2-25). Note that the lower margins of the lungs cross the 6th, 8th, and 10th ribs at the midclavicular lines, the midaxillary lines, and the sides of the vertebral column, respectively; the lower margins of the pleura cross, at the same points, the 8th, 10th, and 12th ribs, respectively. The distance between the two borders corresponds to the costodiaphragmatic recess. (See page 84.) Clinical Notes Pleural Reflections It is hardly necessary to emphasize the importance of knowing the surface markings of the pleural reflections and the lobes of the lungs. When listening to the breath sounds of the respiratory tract, it should be possible to have a mental image of the structures that lie beneath the stethoscope. The cervical dome of the pleura and the apex of the lungs extend up into the neck so that at their highest point they lie about 1 in. (2.5 cm) above the clavicle (Figs. 2-6, 2-13, and 2-23). Consequently, they are vulnerable to stab wounds in the root of the neck or to damage by an anesthetist’s needle when a nerve block of the lower trunk of the brachial plexus is being performed. Remember also that the lower limit of the pleural reflection, as seen from the back, may be damaged during a nephrectomy. The pleura crosses the 12th rib and may be damaged during removal of the kidney through an incision in the loin.

Figure 2-26 Surface markings of the heart.

Heart For practical purposes, the heart may be considered to have both an apex and four borders. The apex, formed by the left ventricle, corresponds to the apex beat and is found in the fifth left intercostal space 3.5 in. (9 cm) from the midline (Fig. 2-26). The superior border, formed by the roots of the great blood vessels, extends from a point on the second left costal cartilage (remember sternal angle) 0.5 in. (1.3 cm) from the edge of the sternum to a point on the third right costal cartilage 0.5 in. (1.3 cm) from the edge of the sternum (Fig. 2-26). The right border, formed by the right atrium, extends from a point on the third right costal cartilage 0.5 in. (1.3 cm) from the edge of the sternum downward to a point on the sixth right costal cartilage 0.5 in. (1.3 cm) from the edge of the sternum (Fig. 2-26). The left border, formed by the left ventricle, extends from a point on the second left costal cartilage 0.5 in. (1.3 cm) from the edge of the sternum to the apex beat of the heart (Fig. 2-26). The inferior border, formed by the right ventricle and the apical part of the left ventricle, extends from the sixth P.73
right costal cartilage 0.5 in. (1.3 cm) from the sternum to the apex beat (Fig. 2-26). Clinical Notes Position and Enlargement of the Heart The surface markings of the heart and the position of the apex beat may enable a physician to determine whether the heart has shifted its position in relation to the chest wall or whether the heart is enlarged by disease. The apex beat can often be seen and almost always can be felt. The position of the margins of the heart can be determined by percussion. Thoracic Blood Vessels The arch of the aorta and the roots of the brachiocephalic and left common carotid arteries lie behind the manubrium sterni (Fig. 2-2). The superior vena cava and the terminal parts of the right and left brachiocephalic veins also lie behind the manubrium sterni. The internal thoracic vessels run vertically downward, posterior to the costal cartilages, 0.5 in. (1.3 cm) lateral to the edge of the sternum (Figs. 2-9 and 2-10), as far as the sixth intercostal space. The intercostal vessels and nerve (“vein, artery, nerve”—VAN—is the order from above downward) are situated immediately below their corresponding ribs (Fig. 2-8). Mammary Gland The mammary gland lies in the superficial fascia covering the anterior chest wall (Fig. 2-20). In the child and in men, it is rudimentary. In the female after puberty, it enlarges and assumes its hemispherical shape. In the young adult female, it overlies the second to the sixth ribs and their costal cartilages and extends from the lateral margin of the sternum to the midaxillary line. Its upper lateral edge extends around the lower border of the pectoralis major and enters the axilla. In middle-aged multiparous women, the breasts may be large and pendulous. In older women past menopause, the adipose tissue of the breast may become reduced in amount and the hemispherical shape lost; the breasts then become smaller, and the overlying skin is wrinkled. The structure of the mammary gland is described fully on page 427. Clinical Problem Solving Study the following case histories and select the best answer to the questions following them. On percussing the anterior chest wall of a patient, you find the right margin of the heart to lie 2 in. (5 cm) to the right of the edge of the sternum. 1. Which chamber of the heart is likely to be enlarged? (a) The left ventricle (b) The left atrium (c) The right ventricle (d) The right atrium View Answer1. D A 31-year-old soldier received a shrapnel wound in the neck during the Persian Gulf War. Recently, during a physical examination, it was noticed that when he blew his nose or sneezed, the skin above the right clavicle bulged upward. 2. The upward bulging of the skin could be explained by (a) injury to the cervical pleura. (b) damage to the suprapleural membrane. (c) damage to the deep fascia in the root of the neck. (d) ununited fracture of the first rib. View Answer2. B. The suprapleural membrane prevents the cervical dome of the pleura from bulging up into the neck. A 52-year-old woman was admitted to the hospital with a diagnosis of right-sided pleurisy with pneumonia. It was decided to remove a sample of pleural fluid from her pleural cavity. The resident inserted the needle close to the lower border of the eighth rib in the anterior axillary line. The next morning he was surprised to hear that the patient had complained of altered skin sensation extending from the point where the needle was inserted downward and forward to the midline of the abdominal wall above the umbilicus. 3. The altered skin sensation in this patient after the needle thoracostomy could be explained by which of the following? (a) The needle was inserted too low down in the intercostal space. (b) The needle was inserted too close to the lower border of the eighth rib and damaged the eighth intercostal nerve. (c) The needle had impaled the eighth rib. (d) The needle had penetrated too deeply and pierced the lung. View Answer3. B A 68-year-old man complained of a swelling in the skin on the back of the chest. He had noticed it for the last 3 years and was concerned because it was rapidly enlarging. On examination, a hard lump was found in the skin in the right scapula line opposite the seventh thoracic vertebra. A biopsy revealed that the lump was malignant. 4. Because of the rapid increase in size of the tumor, which of the following lymph nodes were examined for metastases? (a) Superficial inguinal nodes (b) Anterior axillary nodes (c) Posterior axillary nodes (d) External iliac nodes (e) Deep cervical nodes View Answer4. C A 65-year-old man and a 10-year-old boy were involved in a severe automobile accident. In both patients the thorax had been badly crushed. Radiographic examination revealed that the man had five fractured ribs but the boy had no fractures. 5. What is the most likely explanation for this difference in medical findings? (a) The patients were in different seats in the vehicle. (b) The boy was wearing his seat belt and the man was not. (c) The chest wall of a child is very elastic, and fractures of ribs in children are rare. (d) The man anticipated the impact and tensed his muscles, including those of the shoulder girdle and abdomen. View Answer5. C On examination of a posteroanterior chest radiograph of an 18-year-old woman, it was seen that the left dome of the diaphragm was higher than the right dome and reached to the upper border of the fourth rib. 6. The position of the left dome of the diaphragm could be explained by one of the following conditions except which? (a) The left lung could be collapsed. (b) There is a collection of blood under the diaphragm on the left side. (c) There is an amebic abscess in the left lobe of the liver. (d) The left dome of the diaphragm is normally higher than the right dome. (e) There is a peritoneal abscess beneath the diaphragm on the left side. View Answer6. D A 43-year-old man was involved in a violent quarrel with his wife over another woman. In a fit of rage, the wife picked up a carving knife and lunged forward at her husband, striking his anterior neck over the left clavicle. The husband collapsed on the kitchen floor, bleeding profusely from the wound. The distraught wife called an ambulance. 7. On examination in the emergency department of the hospital, the following conditions were found except which? (a) A wound was seen about 1 in. (2.5 cm) wide over the left clavicle. (b) Auscultation revealed diminished breath sounds over the left hemithorax. (c) The trachea was deflected to the left. (d) The left upper limb was lying stationary on the table, and active movement of the small muscles of the left hand was absent. (e) The patient was insensitive to pin prick along the lateral side of the left arm, forearm, and hand. View Answer7. E. The lower trunk of the brachial plexus was cut by the knife. This would explain the loss of movement of the small muscles of the left hand. It would also explain the loss of skin sensation that occurred in the C8 and T1 dermatomes on the medial, not on the lateral, side of the left forearm and hand. The knife had also pierced the left dome of the cervical pleura, causing a left pneumothorax with left-sided diminished breath sounds and a deflection of the trachea to the left. A 72-year-old man complaining of burning pain on the right side of his chest was seen by his physician. On examination the patient indicated that the pain passed forward over the right sixth intercostal space from the posterior axillary line forward as far as the midline over the sternum. The physician noted that there were several watery blebs on the skin in the painful area. 8. The following statements are correct except which? (a) This patient has herpes zoster. (b) A virus descends along the cutaneous nerves, causing dermatomal pain and the eruption of vesicles. (c) The sixth right intercostal nerve was involved. (d) The condition was confined to the anterior cutaneous branch of the sixth intercostal nerve. View Answer8. D. The skin over the sixth intercostal space is innervated by the lateral cutaneous branch as well as the anterior cutaneous branch of the sixth intercostal nerve. An 18-year-old woman was thrown from a horse while attempting to jump a fence. She landed heavily on the ground, striking the lower part of her chest on the left side. On examination in the emergency department she was conscious but breathless. The lower left side of her chest was badly bruised, and the 9th and 10th ribs were extremely tender to touch. She had severe tachycardia, and her systolic blood pressure was low. 9. The following statements are possibly correct except which? (a) There was evidence of tenderness and muscle spasm in the left upper quadrant of the anterior abdominal wall. (b) A posteroanterior radiograph of the chest revealed fractures of the left 9th and 10th ribs near their angles. (c) The blunt trauma to the ribs had resulted in a tear of the underlying spleen. (d) The presence of blood in the peritoneal cavity had irritated the parietal peritoneum, producing reflex spasm of the upper abdominal muscles. (e) The muscles of the anterior abdominal wall are not supplied by thoracic spinal nerves. View Answer9. E. The 7th to the 11th intercostal nerves supply the muscles of the anterior abdominal wall. Review Questions Multiple-Choice Questions Select the best answer for each question. 1. The following statements concerning structures in the intercostal space are correct except which? (a) The anterior intercostal arteries of the upper six intercostal spaces are branches of the internal thoracic artery. (b) The intercostal nerves travel forward in an intercostal space between the internal intercostal and innermost intercostal muscles. (c) The intercostal blood vessels and nerves are positioned in the order of vein, nerve, and artery from superior to inferior in a subcostal groove. (d) The lower five intercostal nerves supply sensory innervation to the skin of the lateral thoracic and anterior abdominal walls. (e) The posterior intercostal veins drain backward into the azygos and hemiazygos veins. View Answer1. C. The order from superior to inferior is intercostal vein, artery, and nerve. 2. The following statements concerning the diaphragm are correct except which? (a) The right crus provides a muscular sling around the esophagus and possibly prevents regurgitation of stomach contents into the esophagus. (b) On contraction, the diaphragm raises the intra- abdominal pressure and assists in the return of the venous blood to the right atrium of the heart. (c) The level of the diaphragm is higher in the recumbent position than in the standing position. (d) On contraction, the central tendon descends, reducing the intrathoracic pressure. (e) The esophagus passes through the diaphragm at the level of the eighth thoracic vertebra. View Answer2. E. The esophagus passes through the diaphragm at the level of the 10th thoracic vertebra. 3. The following statements concerning the intercostal nerves are correct except which? (a) They provide motor innervation to the peripheral parts of the diaphragm. (b) They provide motor innervation to the intercostal muscles. (c) They provide sensory innervation to the costal parietal pleura. (d) They contain sympathetic fibers to innervate the vascular smooth muscle. (e) The 7th to the 11th intercostal nerves provide sensory innervation to the parietal peritoneum. View Answer3. A. They provide sensory innervation to the pleura and peritoneum covering the peripheral parts of the diaphragm. 4. To pass a needle into the pleural space (cavity) in the midaxillary line, the following structures will have to be pierced except which? (a) Internal intercostal muscle (b) Levatores costarum (c) External intercostal muscle (d) Parietal pleura (e) Innermost intercostal muscle View Answer4. B. The levator costarum is located on the back away from the area involved. 5. The following statements concerning the thoracic outlet (anatomic inlet) are true except which? (a) The manubrium sterni form the anterior border. (b) On each side, the lower trunk of the brachial plexus and the subclavian artery emerge through the outlet and pass laterally over the surface of the first rib. (c) The body of the seventh cervical vertebra forms the posterior boundary. (d) The first ribs form the lateral boundaries. (e) The esophagus and trachea pass through the outlet. View Answer5. C. The body of the first thoracic vertebra forms the posterior boundary. 6. The following statements concerning the thoracic wall are correct except which? (a) The trachea bifurcates opposite the manubriosternal joint (angle of Louis) in the midrespiratory position. (b) The arch of the aorta lies behind the body of the sternum. (c) The apex beat of the heart can normally be felt in the left intercostal space about 3.5 in. (9 cm) from the midline. (d) The lower margin of the right lung on full inspiration could extend down in the midclavicular line to the eighth costal cartilage. (e) All intercostal nerves are derived from the anterior rami of thoracic spinal nerves. View Answer6. B. The arch of the aorta lies behind the manubrium sterni. Completion Questions Select the phrase that best completes each statement. 7. Clinicians define the thoracic outlet as (a) the lower opening in the thoracic cage. (b) the gap between the crura of the diaphragm. (c) the esophageal opening in the diaphragm. (d) the upper opening in the thoracic cage. (e) the gap between the sternal and costal origins of the diaphragm. View Answer7. D 8. The costal margin is formed by (a) the 6th, 8th, and 10th ribs. (b) the inner margins of the 1st ribs. (c) the edge of the xiphoid process. (d) the costal cartilages of the 7th, 8th, 9th, and 10th ribs. (e) the costal cartilages of the 7th to the 10th ribs and the ends of the cartilages of the 11th and 12th ribs. View Answer8. E 9. The lower margin of the left lung in midrespiration crosses (a) the 6th, 8th, and 10th ribs. (b) the 7th, 8th, and 9th ribs. (c) the 10th, 11th, and 12th ribs. (d) the 8th rib only. (e) the 6th, 11th, and 12th ribs. View Answer9. A 10. The suprapleural membrane is attached laterally to the margins of (a) the 1st rib. (b) the 6th, 8th, and 10th ribs. (c) the manubriosternal junction. (d) the 2nd rib. (e) the xiphoid cartilage. View Answer10. A 11. The mammary gland in the young adult female overlies (a) the 1st to the 5th ribs. (b) the 2nd to the 6th ribs. (c) the 1st and 2nd ribs. (d) the 2nd and 3rd ribs. (e) the 4th to the 6th ribs. View Answer11. B 12. The parietal pleura (a) is sensitive only to the sensation of stretch. (b) is separated from the pleural space by endothoracic fascia. (c) is sensitive to the sensations of pain and touch. (d) receives its sensory innervation from the autonomic nervous system. (e) is formed from splanchnopleuric mesoderm. View Answer12. C Fill-in-the-Blank Questions Fill in the blank with the best answer. 13. The thoracic duct passes through the ________ opening in the diaphragm. 14. The superior epigastric artery passes through the ________ opening in the diaphragm. 15. The right phrenic nerve passes through the ________ opening in the diaphragm. 16. The left vagus nerve passes through the ________ opening in the diaphragm. (a) aortic (b) esophageal (c) caval (d) none of the above View Answer13. A 14. D. The superior epigastric artery enters the anterior abdominal wall between the sternal and the costal origins of the diaphragm. 15. C 16. B 17. The aortic opening in the diaphragm lies at the level of the ________ thoracic vertebra. 18. The xiphisternal joint lies at the level of the ________ thoracic vertebra. 19. The caval opening in the diaphragm lies at the level of the ________ thoracic vertebra. (a) 10th (b) 12th (c) 8th (d) 9th (e) 7th View Answer17. B 18. D 19. C Multiple-Choice Questions Read the case history and select the best answer to the question following it. A 35-year-old man complaining of severe pain in the lower part of his left chest was seen by his physician. The patient had been coughing for the last 4 days and was producing blood-stained sputum. He had an increased respiratory rate and had a pyrexia of 104°F. On examination, the patient was found to have fluid in the left pleural space. 20. With the patient in the standing position, the pleural fluid would most likely gravitate down to the (a) oblique fissure. (b) cardiac notch. (c) costomediastinal recess. (d) horizontal fissure. (e) costodiaphragmatic recess. View Answer20. E. This patient started his illness with an upper respiratory infection, which he ignored. Now he has left-sided pneumonia complicated by pleurisy. With pleurisy, the inflammatory exudate may remain at the site of the pneumonia. If the pleural fluid is excessive and the patient assumes the upright position, the fluid may gravitate downward to the lowest part of the pleural space—namely, the costodiaphragmatic recess.

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