The Lung, Pleura, Diaphragm, and Chest Wall

Editors: Shields, Thomas W.; LoCicero, Joseph; Ponn, Ronald B.; Rusch, Valerie W.

Title: General Thoracic Surgery, 6th Edition

Copyright 2005 Lippincott Williams & Wilkins

> Table of Contents > Volume I - The Lung, Pleura, Diaphragm, and Chest Wall > Section I - Anatomy of the Chest Wall and Lungs > Chapter 1 - Anatomy of the Thorax

Chapter 1

Anatomy of the Thorax

Charles E. Blevins

The thorax is a flexible, airtight cage, the framework of which comprises the most continuously active combination of skeletal, muscular, and articulating tissues in the body. Its primary function is to produce movements responsible for ventilation of the lungs. It also affords protection for thoracic viscera and support for the upper extremities, but such responsibilities are secondary to the vital function of producing the alternating changes in pressure required for inflation and deflation of the lungs. Such pressure changes must be orderly, well coordinated, and accompanied by close compliance of the lungs with changes in thoracic dimensions. The volume and rate of air movement must be compatible with vital needs for oxygen under a variety of conditions. To meet such requirements, a uniquely functional anatomic apparatus is required.

RESPIRATORY MOVEMENTS

Movements of the thorax are the result of both active and passive events. During inspiration, the thorax is enlarged actively by coordinated muscle contractions. As a direct result of increased thoracic dimensions, intrathoracic, intrapleural, and intrapulmonic pressures are reduced sequentially so that atmospheric air is forced into the lungs. Expiration is a passive event, largely a result of the relaxation of forces generated during inspiration. It is marked by the return of thoracic dimensions to resting levels and by increased pressure within the chest, pleural cavities, and lungs. Muscle activity may facilitate the expiratory phase of breathing, but it is not essential.

Inspiratory movements enlarge the thorax in all dimensions. They are a blend of efforts directed in the anteroposterior, bilateral, and superoinferior axes. An increase in anteroposterior dimensions is marked by forward and upward movement of the lower part of the sternum, which is called the pump handle movement. The sternum is anchored more firmly at its upper extent by relatively short ribs and costal cartilages than at its lower limits, where both ribs and cartilages are longer. Because the points of pivot of the ribs are located at their vertebral articulations, elevation of the ribs lifts the body of the sternum outward and forward. The greatest excursion occurs at the level of the longest ribs, that is, ribs 5 to 7. The axis for such movement is on a line drawn through the head, neck, and tubercle of each rib (Fig. 1-1).

During normal quiet respiration, the ribs are elevated by contraction of the intercostal muscles. Taylor (1960) and Campbell (1955) reported that the scalene muscles also aid in elevation in some individuals. Jones and associates (1953) reported that the effect of muscles within individual intercostal spaces is apparently small but that synchronous contraction of all intercostal muscles is sufficient to elevate the rib cage as a unit. The resultant increase in anteroposterior dimension is greatest at the level of ribs 5 to 7 (see Fig. 1-1).

Increase in bilateral dimensions is marked by upward and lateral excursion in the vicinity of the midaxillary line. The greatest degree of movement is noted in ribs 7 to 10, the costal cartilages of which descend and then ascend before articulation with the sternum. Because the middle of each rib cartilage unit is lower than either costovertebral or costosternal articulations, elevation swings each unit upward and laterally, much like the action of lifting a bucket handle upward toward the middle of its arc of swing (Fig. 1-2). This action is accomplished by contraction of intercostal muscles also, but Cherniack and Cherniack (1961) suggested that it is facilitated by muscle fibers of the diaphragm that are perpendicular to the costal margin.

The greatest increase in thoracic dimensions during inspiration is in the superoinferior dimensions. It is accomplished by contraction of the diaphragm, which is generally described as dome shaped. The dome, however, is uneven; its anterolateral attachments are at higher levels than its posterolateral attachments. Furthermore, the dome is indented by the heart and may present two domes, one related to the liver and one related to the stomach and spleen. Contraction of most of its muscle fibers flattens the diaphragm against the abdominal viscera, thereby increasing vertical intrathoracic dimensions. Contraction of its peripheral or costal

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muscle fibers also may produce an outward flaring of the lowest costal margin. During quiet respiration, the diaphragm undergoes an excursion of about 1 to 2 cm, but it may move as much as 6 to 7 cm during deep breathing. The lower ribs are believed to be helpful in resisting upward and medial pull of the diaphragm as a result of stabilization by the serratus posterior inferior muscles. The quadratus lumborum may stabilize the twelfth rib, but its effect on respiration is probably insignificant.

Fig. 1-1. The pump handle movement in breathing. Compare the position of the sternum and ribs at the beginning (A) and the end (B) of inspiration. Note the increase in anteroposterior dimensions.

The diaphragm and intercostal muscles are therefore the primary muscles of inspiration. Movements of the diaphragm account for 75% to 80% of pulmonary ventilation during quiet respiration, compared with 20% to 25% contributed by the intercostal muscles, mainly the external intercostals and the anterior portions of the internal intercostals. During severe or labored breathing, however, other skeletal muscles may be used. The sternocleidomastoid, serratus posterosuperior, and levatores costarum may be active in elevation of the ribs. Muscles of the extremities also may be helpful in moments of severe need. With the torso in fixed position, movement of the arms and shoulders away from the thorax may be sufficient to enlarge thoracic dimensions to a small but sometimes necessary degree. Deltoid, trapezius, pectoral, and latissimus dorsi muscles are involved in such activity.

Expiration can occur only when intrapulmonic pressure exceeds that of the atmosphere. At the end of inspiration, the lungs are inflated and stretched. Inspiratory muscles have reached optimal efficiency in expanding the rib cage against atmospheric pressure. At this point, elastic resistance of lung tissue is at first equal to and then greater than muscular forces that would retain the expanded state of the thorax. The lungs recoil elastically, and the consequent increase in intrapulmonic pressure is sufficient to force air out of the lungs. Both soft and hard tissues of the thoracic wall comply passively with the reduction of lung volume, aided by atmospheric pressure directed against them. Expiration stops when intrapulmonic pressure is once again equal to atmospheric pressure. In quiet breathing, expiration is accomplished almost exclusively by elastic recoil of the lungs and rib cage. During vigorous or carefully controlled expiration, however, such as while singing, shouting, abdominal straining, or playing a wind instrument, muscles of the abdominal wall may aid in the reduction of thoracic dimensions by compression of abdominal viscera against the diaphragm.

Fig. 1-2. The bucket handle movement in breathing. Compare the distance of the ribs from the central axis of the thorax at the beginning (A) and the end (B) of inspiration. Note the increase in lateral dimensions.

Although the change from inspiratory to expiratory efforts thus represents a shift from active to passive events, the change in airflow is not a chaotic event. Rather, it is well regulated by the diaphragm, which continues to contract with decreasing efficiency but does not reach the zero

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point until the middle of expiration. In this respect, it is similar to the action of limb musculature, in which gradual relaxation of flexor muscles prevents uncoordinated movement of an extremity in the opposite direction by antagonistic extensors. As described by Agostini and Torri (1962), during maximal breathing efforts, the diaphragm also contracts toward the end of vigorous expiration, limiting the extent to which the lungs can collapse.

SURFACE LANDMARKS AND STRUCTURES SUPERFICIAL TO THE THORAX

The thoracic surgeon is primarily concerned with the thoracic wall and the thoracic contents; however, a few overall considerations of structures related to surface features are helpful in orientation to deeper structures of the thorax itself (Fig. 1-3). In all but the most obese subjects, the outline of the sternum can be visualized in the thoracic midline. Extending laterally and slightly upward from the jugular notch of the sternum, the clavicles curve forward and then backward toward the shoulders. From the lowermost margin of the body of the sternum, the lower margin of the rib cage diverges bilaterally to reach its lowest level at the midaxillary line.

The outline of the sternocleidomastoid muscles may be seen extending diagonally upward from the upper part of the anterior surface of the manubrium of the sternum and the medial one third of the clavicle toward the base of the skull. Immediately below the clavicle, the outline of the pectoralis major muscle is evident. These muscles extend bilaterally from broad clavicular, sternal, and costal origins, converge toward the axilla, and form a bilaminar, U-shaped tendon that attaches to the lateral lip of the intertubercular sulcus of the humerus. The lower margin of each pectoralis major muscle forms the anterior fold of the axilla. The pectoralis major muscles are supplied by medial and lateral pectoral nerves from the brachial plexus and are versatile in function. They adduct and rotate the arm medially and in addition may elevate it (clavicular portion) or depress it (sternocostal portion). If the shoulder girdle is held in fixed position, these muscles also may elevate the upper ribs in forced inspiration. During artificial respiration, pulling the flexed upper extremity toward the head may also force the pectoralis major muscles to elevate the upper ribs.

Fig. 1-3. Surface features and details of structures superficial to the thoracic wall in the pectoral region and the axilla. Musculoskeletal features are shown on the left. Surface features and cutaneous innervation are shown on the right. Cutaneous branches of the fifth intercostal space are illustrated as typical of other intercostal spaces not shown. Common lines of reference are shown. A, midsternal line; B, lateral sternal line; C, midclavicular line; D, anterior axillary fold; E, posterior axillary fold.

Deep to the pectoralis major muscles lie the pectoralis minor muscles. They originate by slips from the second to fifth ribs and converge upward to a tendon that inserts on the coracoid process of the scapula. Supplied also by the medial and lateral pectoral nerves, these muscles are active in depressing and rotating the shoulders downward.

In thin, muscular subjects, the serratus anterior muscles can be visualized along the anterolateral aspects of the thoracic wall. They originate by slips from the upper eight ribs. They are applied closely to the thoracic wall as they pass upward and laterally to attach to the anterior surface and medial border of the scapula on either side. They hold the scapulae toward the thoracic wall and are important in adduction and elevation of the arms above the horizontal position during scapulohumeral movement. On each side, the serratus anterior is supplied by the long thoracic nerve, which passes downward in the midaxillary line on the external surface of the muscle.

In men, the nipple lies near the lower border of the pectoralis major muscles, just lateral to the midclavicular line, over the fourth intercostal space or fourth or fifth ribs. Nipple position is inconsistent in women because of the variable size of the mammary gland, which lies generally over the second to sixth ribs. The axillary tail extends upward into the axilla along the lower border of the pectoralis major muscle.

Cutaneous innervation of the anterolateral thoracic wall is supplied by supraclavicular nerves and terminal filaments of thoracic spinal nerves. Skin above, overlying, and slightly below the clavicle is supplied by supraclavicular nerves, which arise as terminal filaments of spinal nerves C3 and C4. The remainder of the thoracic wall is supplied by anterior cutaneous and lateral cutaneous branches of thoracic spinal nerves.

The posterior aspect of the thorax is covered almost completely by superficial muscles of the back, but a few bony landmarks are either visible or palpable (Fig. 1-4). In the midline, the spinous process of the seventh cervical vertebra (vertebra prominens) stands out clearly. Below this process, the spine of the first thoracic vertebra may be equally visible. Spines of the remaining 11 thoracic vertebrae extend downward so that the tip of each overlies the body of

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the vertebra below. In the midthoracic levels, the vertebral spines may be sufficiently long to overlie the intervertebral disc below the subjacent vertebra. The medial border of each scapula lies lateral to the midline at the level of the second to seventh ribs. The spine of the scapula extends diagonally upward from the medial border at about the third thoracic vertebra to end in the acromion at the shoulder.

Fig. 1-4. Surface features and details of structures superficial to the posterior aspect of the thorax. The scapula has been displaced upward and laterally on the right side to permit a better view of muscles superficial to the thorax.

Surface contours of the back of the thorax are formed by muscles of the shoulder and scapular region; these muscles support and help move the upper extremity. Posterolateral margins of the neck and uppermost limits of the shoulder are marked by the trapezius muscles. Each of these arises from broad origins, including the superior nuchal line of the occipital bone, the ligamentum nuchae of the neck, the spine of the seventh cervical vertebra, and spines and supraspinous ligaments of all thoracic vertebrae. Fibers sweep downward, laterally, and upward toward the shoulder, where they insert on the spine and acromion of the scapula and on the lateral one third of the clavicle. In lower cervical and upper thoracic levels, their aponeurotic origin is sufficiently devoid of muscle fibers to allow spines of thoracic vertebrae to be easily palpable. The trapezius muscles are supplied by spinal accessory nerves and by filaments from cervical spinal levels C3 and C4. They are powerful stabilizers of the scapulae and shoulders and can elevate, depress, or adduct the scapulae, thereby aiding in the entire spectrum of scapulohumeral movements.

Lower and lateral parts of the back of the thorax are covered by the latissimus dorsi muscles. These muscles arise by broad aponeurotic origins, from spines of lower thoracic vertebrae, the lumbodorsal fascia, and the iliac crests. Additional slips of muscle also arise from outer surfaces of the lower three or four ribs and blend with overlying components. Muscle fibers converge upward to insert by tendons into the intertubercular groove of the humerus on each side. In their upper thirds, these muscles converge with the teres major muscles to form the posterior folds of the axillae. The latissimus dorsi muscles are adductors, extensors, and medial rotators of the arm. Each is supplied by a thoracodorsal nerve from the posterior cord of the brachial plexus. Because of attachment to the ribs, the latissimus dorsi muscles also can be considered accessory muscles of respiration.

The lower border of the trapezius muscle overlies the upper border of the latissimus dorsi. Near the point of overlap, a triangle is formed by the lateral border of the trapezius, the upper border of the latissimus dorsi, and the medial border of the scapula. Save for lower fibers of the rhomboid muscles, this area is free of an intervening mass of muscle tissue. Because a stethoscope placed over this triangle can detect respiratory sounds relatively free of distortion, it is called the triangle of auscultation.

Deep to the trapezius and latissimus dorsi muscles lies a layer of muscles involved in scapular movements and, to a lesser degree, movements of the ribs. Those related to the scapula are the levator scapulae, rhomboid major, and rhomboid minor muscles. The thin levator scapulae extend from the transverse processes of the first three or four cervical vertebrae diagonally downward to attach at the superior angle of the scapula on each side. The rhomboid minor may be fused with the rhomboid major. It extends from spines of the seventh cervical vertebra and first thoracic vertebra to the medial border of the scapula near the base of its spine. The rhomboid major arises from the spines of the second to fifth thoracic vertebrae and the supraspinous ligament between these vertebrae and is attached to the medial border of the scapula, usually below the spine of the scapula. The levator scapulae, rhomboid major, and rhomboid minor elevate, adduct, and retract the scapula. All are supplied by the dorsal scapular nerve, but the levator scapulae are supplied also by branches from C4 and C5.

The serratus posterior muscles are said to be inspiratory muscles and thus merit brief attention. The serratus posterosuperior muscles arise by aponeuroses from the ligamentum nuchae and spinous processes of the seventh cervical vertebra and the first to third thoracic vertebrae and are attached to the upper borders of the first three to five ribs. They are supplied by ventral rami of segmental spinal nerves (intercostal nerves) and are said to be active in the elevation of the upper ribs. The serratus posterior inferior muscles take aponeurotic origins from spinous processes of the lower two thoracic and upper two lumbar vertebrae; they insert by muscular slips on the lower three or four ribs. They are supplied also by ventral rami of segmental spinal nerves and are presumably able to prevent upward displacement of their ribs during inspiration.

Innervation of skin over the back is provided by medial cutaneous branches of dorsal rami of C4, C5, C8, T1, and T2 and by medial and lateral cutaneous branches of T3 T10. Considerable overlap and asymmetry of these nerves have been described by Johnston (1908).

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ANATOMIC FEATURES

Firm structural support for the thorax is provided by the sternum, 10 pairs of costae (ribs and costal cartilages), 2 pairs of ribs without cartilage, and 12 thoracic vertebrae and their intervertebral discs. Collectively, these components surround a cavity that is reniform in cross section, related to the neck above by a narrow thoracic inlet and to the abdominal cavity below by a larger thoracic outlet. The inlet is surrounded by the manubrium of the sternum, the first ribs, and the first thoracic vertebra. Its anterior boundaries lie about 1 inch below the posterior limits. The inlet is roofed by bilateral thickened endothoracic fascia (Sibson's fascia or suprapleural membrane) and subjacent parietal pleurae, which project upward into the base of the neck. Additional details of soft tissue relations of the thoracic inlet are considered later in this chapter (see Surface Anatomy). The outlet is formed by the xiphoid process, fused costal cartilages of ribs 7 to 10, the anterior portions of the eleventh ribs, the shafts of the twelfth ribs, and the body of the twelfth thoracic vertebra. The anterior margin of the outlet is at the level of the tenth thoracic, the lateral limits at the second lumbar, and the posterior margin at the twelfth thoracic vertebra. The outlet is therefore higher at its anterior margin than at its posterior limit and reaches its lowest level in the lateral aspect near the midaxillary line. It is sealed off from the abdominal cavity by the diaphragm.

Sternum and Its Joints

The sternum is an elongated, flat bone that lies in the anterior midline. It is 15 to 20 cm long and is formed from cartilaginous precursors that ossify separately to form three components: the manubrium, body, and xiphoid process (Fig. 1-5).

The manubrium is about 5 cm wide in its upper half and 2.5 to 3.0 cm wide in its lower half. Its upper border is thickened and marked on either side by a notch for articulation with the clavicle. Centrally, an indentation is present, which, together with the sternal ends of each clavicle, forms the jugular, suprasternal notch. The widest portion of the manubrium is marked by bilateral indentations, the costal incisura, to accommodate articulation of the first costal cartilage. At the lower limits, each lateral margin of the bone is indented by a demifacet for articulation of the upper half of the second costal cartilage. The lower margin of the manubrium articulates with the body of the sternum.

The body or longest portion of the sternum is slightly more than twice the length of the manubrium. It is slanted at a steeper angle than the manubrium; hence, its articulation with that bone forms an angle, called the sternal angle. The outer border of this angle is readily palpable and lies at the level of the fourth to fifth thoracic vertebrae or their intervening intervertebral disc. The joint is a synchondrosis: Articular surfaces of each bone are covered with hyaline cartilage and are united by fibrocartilage. It is sufficiently flexible to allow movement of the body on the more stable manubrium during respiratory movements. Ossification of the joint may form a synostosis during adult years, thus limiting flexibility, but as noted by Trotter (1934), correlation is not observed between age and its incidence.

Lateral margins of the body exhibit segmental incisurae for articulation of costal cartilages 2 to 7. The incisura for the second costal cartilage is incomplete because it represents only the lower half of the articulation surface that is completed by the demifacet on the lower margin of the manubrium. The body ends at about the level of the tenth to eleventh thoracic vertebrae, where it forms a cartilaginous joint with the xiphoid process.

The xiphoid is a cartilaginous process that is usually ossified by middle age. It is the shortest and thinnest part of the sternum and may occasionally be bifid or perforated. It extends downward for a variable distance to end in the sheath of the rectus abdominis muscle. Its posterior surface is even with that of the sternal body; its anterior surface is somewhat recessed. The xiphoid is flexible at the xiphisternal joint, but it moves with the sternum during respiratory movements. Supportive costoxiphoid ligaments, extending from its anterior surface to the front of the seventh costal cartilage, prevent its backward displacement by contractions of the diaphragm.

The midline of the sternum is almost completely subcutaneous and is therefore easily accessible for sternal puncture, sternal transfusion, or incision during thoracic surgery. Its lateral margins are covered by origins of the sternal components of the pectoralis major muscles.

Ribs and Their Joints

The size and shape of the thorax are largely determined by the ribs and costal cartilages. A rib and its associated cartilage are properly termed a costa. The costae form continuous arches that extend backward for a short distance in relation to the vertebrae, turn forward at the angle, and extend toward the sternum, with which all but two pairs of them articulate directly or indirectly. Developmentally, the costae arise as arched, cartilaginous struts extending serially and horizontally from their respective vertebral bodies to the sternum. As development proceeds, the vertebral ends of each costal pair migrate cephalad. This shift in position is more pronounced in costal pairs 2 to 9, and as a result, the head of each of these ribs becomes pressed against the body of the vertebra immediately above. At the end of the growth period, ribs 2 to 9 articulate with both their own and the immediately rostral vertebrae. The tenth rib may migrate sufficiently to articulate with the ninth and tenth thoracic vertebrae, or it may remain low enough to articulate only with the body of the tenth thoracic vertebra. The eleventh and twelfth ribs migrate only slightly and thus form joints only with their own vertebrae. The angle of costal elements of the thoracic wall relative to the vertebrae and the sternum is therefore the result of cephalic migration of vertebral extremities

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and relative retention of sternal extremities at their original levels.

Fig. 1-5. Anterior view of the skeleton of the thorax and bones of the pectoral girdle. Bilateral asymmetry is evident in the body and xiphoid process of the sternum. The left subcostal arch is slightly higher than the right one.

Ossification is initiated at the bend or angle of the costae. It spreads posteriorly toward the vertebrae and anteriorly toward the sternum. By the time bone deposition stops, the short vertebral portion is completely ossified. Because that part of the costa from the angle forward is longer, its ossification is not complete by the time bone formation ceases. The ossified portion of each costa becomes the rib proper, and the unossified part remains as costal cartilage.

Relations of ribs and their costal cartilages to the sternum and to each other vary at different levels (Fig. 1-6; see Fig. 1-5). The upper seven pairs of ribs articulate directly with the sternum by way of costal cartilages and are therefore called true or vertebrosternal ribs. In contrast, the lower five pairs are called false ribs because they do not articulate with the sternum at all. Of the false ribs, three pairs (the eighth, ninth, and tenth) are called vertebrocostal because their associated cartilages articulate with immediately supradjacent cartilages. The remaining pairs, 11 and 12, terminate in cartilaginous tips, ending in muscles of the abdominal wall. Because their only articulation is with the vertebrae, they are called vertebral ribs.

The costal cartilages change sequentially in length and direction. The first and second costal cartilages are short and follow a slightly downward course. The third and fourth gradually increase in length and are horizontal, or nearly so. The fifth to seventh cartilages extend downward from the tip of their ribs and then turn upward to meet the sternum. Because both ribs and cartilages of these costae are the longest and most flexible, they are maximally involved in the bucket handle movement of the rib. The fused cartilages of ribs 7 to 10 course diagonally upward to the lower end of the sternum to form the infrasternal angle.

Ribs exhibit many similar features, but their form is variable at different levels. They increase in length from the first to the seventh and then gradually shorten to the twelfth. The most common features are characteristic of ribs 3 to 9, which are frequently called typical ribs. From their vertebral to sternal ends, each of these ribs is formed by a head, a neck, and a shaft (Fig. 1-7). The head is enlarged and marked by two facets, separated by an interarticular crest. The upper facet articulates with a facet on the body of the rostral vertebra. A slightly larger inferior facet articulates with a facet on the body of the adjacent vertebra whose number corresponds with that of the rib. The joint formed between costal facets, supradjacent, and adjacent vertebral bodies is termed a costovertebral joint.

The neck of each rib extends dorsolaterally for about 2.5 cm and is marked by a crest on its upper border. The end of the neck and beginning of the shaft are marked by a tubercle. The tubercle bears a roughened elevation and a smooth articular surface. The elevation serves as an attachment for costotransverse ligaments. The articular surface meets a facet on the transverse process of the corresponding vertebra to form the costotransverse joint.

The shaft of the rib extends dorsolaterally for an additional 5.0 to 7.5 cm and then turns gradually forward and downward. The accentuated portion of this forward curvature is called the angle of the rib. The angle marks the lateral extent of the erector spinae muscles of the back. Throughout its course, the shaft is twisted slightly so that its

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superolateral border is rounded and convex. The lower margin of the inferomedial surface is scored by a costal groove for the intercostal vessels and nerves. This groove is most clearly defined on the inner aspect of the posterior half of each rib. The shaft terminates in a small indentation, which forms a hyaline cartilaginous joint with its costal cartilage.

Fig. 1-6. Lateral view of the thoracic cage.

The less typical ribs differ in the following respects. The first rib is shorter than the rest and, beyond its neck, is wider and more curved. The head is small and bears only one facet for articulation with the body of the first thoracic vertebra. The upper and lower surfaces of the shaft are flat, and its edges are sharp. Near the middle of the shaft, a rounded tubercle is present that serves as an attachment for the anterior scalene muscle. Behind the tubercle is a depression where the first rib is crossed by the subclavian artery. A smaller depression for the subclavian vein may sometimes be noted in front of the tubercle.

The second rib is nearly twice the length of the first and articulates with the bodies of the first and second thoracic vertebrae. Its shaft is curved but not twisted and is marked by a roughened tubercle for upper digitations of the serratus anterior muscle.

The eleventh and twelfth ribs are sequentially shorter than supradjacent ones and bear only one articular surface for their corresponding vertebrae. They exhibit poorly defined or completely absent necks, angles, and costal grooves. The length of the twelfth rib is of consequence in renal surgery. Although it is often shorter in a woman than in a man, Hughes (1949) has shown that longer ones, 11 to 14 cm, are more common than shorter ones, 1.5 to 6.0 cm. The posterior margin of parietal pleura normally crosses the twelfth rib at the lateral margin of the erector spinae muscles. If the twelfth rib is short, the surgeon may inadvertently palpate the lower border of the eleventh rib to determine the level for the initial incision. Such an incision

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risks entering the thoracic cavity instead of extraperitoneal tissue or renal fascia behind the kidneys.

Fig. 1-7. A typical rib. A. Inferior view. B. Superior view.

Variations in rib structure may be of clinical significance. The first rib may be fused with the second at the scalene tubercle. This union is usually associated with other variations in the second rib, sternum, or associated thoracic vertebrae. The seventh cervical vertebra may bear a cartilaginous or ossified rib called a cervical rib. Such a rib may be short, or it may be attached to the first costal cartilage or to the manubrium. Variations in the thoracic inlet or the presence of a cervical rib can produce compression of the subclavian artery and the brachial plexus, resulting in compromise of neurovascular supply to the upper extremity. Occasionally, the sternal extremity of the third or fourth rib may be bifid, and the eighth rib may reach the sternum on one or both sides. A lumbar rib may be associated with the first lumbar vertebra.

The structure of the heads of ribs 2 through 9 and the associated vertebrae shows that the costovertebral joints consist of two joint cavities, each composed of costal and vertebral facets. The cavities are separated by a ligament extending from the interarticular crest of the rib to the intervertebral disc. Articular surfaces are covered with fibrous cartilage; joint cavities are surrounded by a synovial articular capsule. The capsule is thickened by radiate ligaments that fan out from the head of the rib to adjacent vertebral bodies.

Costotransverse joints, between the articular tubercle and the transverse process of the rib, are also synovial. Articular surfaces are covered with hyaline cartilage, and the joint is enclosed by a fibrous capsule. The capsule is reinforced by costotransverse ligaments, which connect the neck and tubercle of the rib to the transverse process of its own vertebra and to that immediately above. Motions involved in both the bucket handle and pump handle movements of breathing are permitted by the flexibility of both the costovertebral and costotransverse joints. Fixation of these joints adversely affects pulmonary function.

Intercostal Spaces

The frequency with which the spaces between ribs are used in surgical approaches to the thorax prescribes an understanding of their muscular, fascial, and neurovascular features (Figs. FIG. 1-8,FIG. 1-9,FIG. 1-10,FIG. 1-11). Lying deep to the skin, superficial fascia (tela subcutanea), and muscles related to the thoracic girdle and upper extremity, each intercostal space is traversed by three layers of muscle and their related deep fascia. Both muscles and fascia are attached to periosteum at the upper and lower borders of the ribs. During thoracoplasty, an incision over the body of the rib and subsequent retraction of its periosteum during removal of the rib do not violate the contents of the intercostal spaces.

From the surgical approach, the first layer of tissue to be encountered within the intercostal space is composed of the external intercostal muscles. Their fibers extend diagonally downward and forward from the lower margin of each rib to the upper margin of the subjacent rib. Musculature of this layer is continuous from a posterior position at the tubercle of the rib and posterior fibers of the costotransverse ligament (Fig. 1-12; see FIG. 1-9 and FIG. 1-11) to an anterior position at or near the costal cartilages. At this point, the investing fascia of the muscle continues farther anteriorly to the sternum as the external, anterior intercostal membrane (Fig. 1-13; see Fig. 1-12). Intercostal muscles of the lower seven intercostal spaces interdigitate with the external oblique muscle of the abdominal wall. The next layer encountered consists of the internal intercostal muscles and their fascia. Muscle fibers

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extend downward and backward between costal cartilages in the anteromedial part of the intercostal space and between the ribs proper farther laterally and posteriorly in the intercostal space. The reverse direction of these muscle fibers from those of the external intercostal muscle lends a cross-diagonal supportive force. Musculature of this layer extends from the sternum (see Figs. 1-12 and Fig. 1-13) as far posterior as the angle of the ribs (see Figs. 1-11 and Fig. 1-12). At this point, their investing fasciae form the internal-posterior-intercostal membrane, which attaches to the tubercle of each rib and the adjacent vertebra (see Fig. 1-11). Neurovascular components of the intercostal spaces are encountered immediately deep to these two layers. From above downward, the intercostal vein, artery, and nerve enter the posterior part of the intercostal space (see Figs. 1-11 and Fig. 1-12). In this region, they lie within the endothoracic fascia deep to the internal intercostal membrane and just superficial to parietal pleura (see Fig. 1-12). They remain in this position for a distance of 4 to 6 cm, at which point they gain the space between the internal and innermost intercostal muscles along the costal groove near the angle of the ribs (see Figs. 1-7 and Fig. 1-10, 1-11 and 1-12). The neurovascular component therefore lies in the upper limits of the intercostal space, in contrast to the collateral branches, which lie in the lower limits. The origin and distribution of these neurovascular elements are considered in detail later. Their position with respect to the ribs is important during incision of the intercostal space. Because major intercostal vessels and nerves lie in close relation to the lower border of each rib, incisions near this level are to be avoided. A preferable site is along the upper margin of each rib. Although accessory nerves and vessels may be sectioned at this level, loss of function or sensitivity is negligible. It is equally important, however, to understand that the overlap of adjacent nerves is so great that paralysis and complete anesthesia are seldom produced within one intercostal space unless its nerve, the one above, and the one below are all severed.

Fig. 1-8. Anterior view of the thoracic wall and muscles of the intercostal spaces. The left side of the thorax is intact. The anterior half of the right side has been removed to demonstrate the inner aspect of the posterolateral thoracic wall.

Fig. 1-9. Posterior view of the thoracic wall and muscles of the intercostal spaces. The right side of the thorax is intact. The posterior half of the left side has been removed to show the inner aspect of the anterior thoracic wall.

Fig. 1-10. Relations of structures within an intercostal space. A. Intercostal vessels and nerves are shown. B. Collateral vessels are shown. A, artery; N, nerve; V, vein.

Fig. 1-11. Exposure of the posterior part of intercostal spaces 8, 9, and 10. Note that the intercostal vein (v.), artery (a.), and nerve (n.) lie between the internal intercostal muscle and the innermost intercostal muscle layers. From the intervertebral foramen to the angle of the rib, the intercostal vessels and nerves are covered by the internal intercostal membrane.

The next layer of tissue encountered is less well defined. It consists of the innermost intercostal, subcostal, and transversus thoracis muscles and their fasciae. The innermost intercostals are best developed in the middle portion of the intercostal space (see Figs. 1-9,Fig. 1-10,Fig. 1-11,Fig. 1-12) and may be absent completely in the upper regions of the thoracic wall. They extend between adjacent ribs in the same direction as the internal intercostal muscles. Davies and associates (1932) considered them inner laminae of the internal intercostal muscles. The subcostal muscles extend as a variable number of slips from the lower margin of the angle of the ribs, diagonally across more than one intercostal space to the upper margin of the second or third rib below. The transversus thoracis is a thin layer of muscle on the inner aspect of the anterior thoracic wall. Aponeurotic slips of this muscle extend diagonally upward from the body and xiphoid process of the sternum to costal cartilages. The lowermost fibers of the transversus thoracis are almost horizontal and are continuous with the transversus abdominis muscle of the abdominal wall.

Deep to the third layer of muscles is the endothoracic fascia. It consists of variable amounts of areolar connective tissue, affording a natural cleavage plane for separation of the subjacent pleura from the thoracic wall.

The arterial supply of the intercostal spaces consists of posterior and anterior intercostal arteries. The posterior intercostal arteries of the first and second intercostal spaces arise from the highest intercostal arteries, which are branches of the subclavian artery; those of the remaining nine intercostal spaces are branches of the thoracic aorta. These arteries supply

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most of their respective intercostal spaces except the anteriormost limits. Each gives rise to a posterior branch supplying the spinal cord and deep muscles and skin of the back, an anterior branch running between the vein and nerve in the costal groove, and a collateral branch arising near the angle of the rib and descending to the upper border of the rib below. In the midaxillary line, each anterior branch gives rise to a lateral cutaneous branch, which perforates the intercostal space to supply overlying skin. The posterior intercostal artery coursing below the twelfth rib is called the subcostal artery. It follows a course similar to those above but has no collateral branches.

Fig. 1-12. Summary scheme of structures within an intercostal space. Arteries are shown on the left, nerves on the right.

The anterior intercostal arteries arise as segmental branches of the internal thoracic arteries in the first five or six intercostal spaces and as branches of the musculophrenic arteries in the lower intercostal spaces. Two such arteries are given off in each intercostal space, one passing toward the upper rib and one toward the lower. They continue laterally to anastomose with terminal branches of anterior and collateral branches of the posterior intercostal arteries.

The intercostal spaces are drained by 11 pairs of posterior intercostal veins and one pair of subcostal veins. These vessels follow the course of the posterior intercostal arteries and for the most part are tributaries to the azygos or hemiazygos venous system. They lie above the nerve and artery throughout their course. Major blood flow is directed posteriorly by valves, but terminal vessels also may be tributaries to the internal thoracic veins by way of small anterior intercostal veins. Posterior intercostal veins of the first intercostal space may be tributaries to the brachiocephalic, vertebral, or superior intercostal veins. The second, third, and fourth posterior intercostal veins drain into the superior intercostal vein on each side; these in turn drain into the brachiocephalic vein on the left and into the azygos vein on the right. Right and left subcostal veins join the ascending lumbar veins on their respective sides of the thorax and ascend as the azygos and hemiazygos veins, respectively.

Fig. 1-13. Anterior view of the left half of the thorax. Note the opposing diagonal course of the external intercostal muscle fibers compared with that of the internal intercostal muscle fibers. The external, anterior intercostal membrane extends from the costochondral junction to the sternum in the intercostal spaces.

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Lymphatic drainage of the anterior limits of the upper four or five intercostal spaces enters the sternal, internal thoracic nodes, which lie along the internal thoracic arteries. Their efferent vessels are tributary to a single vessel that joins the bronchomediastinal trunk. These nodes may be invaded commonly by metastases from breast carcinoma. Posterolateral portions of the intercostal spaces are drained by lymphatics that are tributary to one or two nodes near the vertebral ends of each intercostal space. Such nodes also receive lymphatic tributaries from the pleura. Nodes of upper intercostal spaces drain into the thoracic duct; those of the lower spaces are tributary to the cisterna chyli.

The thoracic wall is innervated segmentally by 12 pairs of thoracic spinal nerves. Upper thoracic spinal nerves also supply innervation to the axilla and upper extremity. Lower thoracic spinal nerves also supply portions of the abdominal wall and are called thoracoabdominal nerves. The midthoracic spinal nerves, T4 T6, exhibit the most common pattern and are considered typical nerves to the thoracic wall. Each spinal nerve is formed from a dorsal and a ventral root. The dorsal root contains sensory neurons that are distributed to posterior gray columns of the spinal cord. The ventral root contains somatic motor neurons originating in anterior gray columns of the spinal cord. Near the intervertebral foramen, the dorsal and ventral roots unite to form a mixed spinal nerve. Each spinal nerve gives rise to a small meningeal nerve and then passes out of the intervertebral foramen, to branch into a dorsal and ventral ramus (see Fig. 1-12).

The dorsal ramus of the thoracic spinal nerve passes backward to supply paravertebral back muscles and skin of the back. It forms medial and lateral cutaneous branches. Medial branches supply periosteum, ligaments, and joints of the vertebrae, as well as deep muscles of the back, before terminating in cutaneous filaments. Lateral branches supply the small levator costae muscles and deep back muscles and follow a long descending course before becoming cutaneous. Extensive terminal overlap and anastomoses occur among medial and lateral cutaneous branches of dorsal rami from different spinal levels. Consequently, cutaneous pain is difficult to localize in this region.

Just lateral to the intervertebral foramen, the ventral ramus of the thoracic nerve establishes communications with the sympathetic chain by two branches or rami communicantes (see Fig. 1-12). The white ramus contains preganglionic sympathetic fibers, and the gray ramus contains postganglionic sympathetic fibers. Beyond this point, the ramus continues as the intercostal nerve and is responsible for segmental distribution to skin, muscle, and serous membranes of the thoracic wall. Each intercostal nerve passes backward below the rib in the vicinity of costotransverse ligaments and then gains the costal groove. It continues its course in the plane between the innermost intercostal and internal intercostal muscles. Near the angle of the rib, a collateral branch is given off. This branch passes laterally and then forward in the lower part of the intercostal space, terminating as a lower anterior cutaneous nerve.

Near the midaxillary line, a lateral cutaneous branch is given off. It pierces the intercostal muscles, passes through the serratus anterior muscles, and then forms anterior and posterior cutaneous branches.

Just lateral to the sternal margin, the intercostal nerve lies between transversus thoracis and internal intercostal muscles. At this point, it pierces overlying internal and external intercostal muscles, becomes subcutaneous, and forms anterior and median cutaneous branches.

Each segment of the thoracic wall is thus supplied circumferentially from behind and forward by branches of the dorsal ramus and collateral, lateral, and anterior branches of the ventral ramus. The ventral rami (intercostal nerves) supply the intercostal, subcostal, serratus posterior superior, and transversus thoracis muscles and the skin overlying the intercostal spaces. Although the pattern of innervation for each intercostal space is basically similar, considerable intersegmental overlap is characteristic. For that reason, complete paralysis or anesthesia in only one intercostal space does not occur unless the nerve of that space, as well as the nerves of the intercostal spaces above and below, is sectioned.

SURFACE ANATOMY

Knowledge of the surface relations of lobes and fissures of the lungs is important in percussion, auscultation, and radiographic evaluation of the pulmonary field. Although the lungs are in constant motion during respiration, the surface relations observed by Brock (1954) are essentially as described in Chapter 5. Knowledge of the topography of the various fissures of the lung is helpful in localizing abnormal pulmonary sounds as well as in localizing abnormal densities in radiographs of the chest (Figs. 1-14 and FIG. 1-15).

Fig. 1-14. Anterior view of the thorax showing surface relations of pleura and lungs. Pleural borders subjacent to bone are shown by interrupted lines.

Fig. 1-15. Lateral view of the thorax showing surface relations of pleura and lungs.

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For surgical purposes, the lungs and pleura may be considered coextensive, with their respective costal, mediastinal, and diaphragmatic surfaces separated only by a film of serous fluid. In quiet respiration, those parts of the lung within the costomediastinal and costodiaphragmatic recesses are inflated insufficiently to be identified by percussion. Percussible limits of the lower border of the lung normally lie at slightly higher levels than the lower limits of the pleura. The frequency with which indwelling lines or catheters are surgically inserted into the subclavian veins and the consequence of damaging nearby pleura or neurovascular structures require special knowledge of soft tissue relations at the thoracic inlet (Figs. 1-16 and FIG. 1-17). On both sides of the thorax, the subclavian vein lies deep to the clavicle and crosses the first rib anterior to the attachment of the serratus anterior muscle on the scalene tubercle of the first rib. The second part of the subclavian artery passes posterior to the scalenus anterior muscle and its third part lies lateral to the attachment of muscle on the first rib. Likewise, components of the brachial plexus pass behind and then lateral to the scalenus anterior muscle. More important, in relation to pulmonary function, the cupola of the pleura is consistently related to the inferior and medial border of the scalenus anterior muscle. In this position, the cupola reaches its most superficial position and therefore is susceptible to damage during invasive surgical procedures. This portion of the cupola also is crossed superficially by the phrenic nerve and the vagus nerve. On the right side, the vagus nerve descends within the carotid fascia between the internal jugular vein and the common carotid artery and subsequently crosses the first part of the subclavian artery to enter the thorax between the common carotid and subclavian arteries. On the left side, the vagus nerve lies on the cupola of the pleura between the internal jugular vein and the common carotid artery to enter the thorax between the common carotid and subclavian arteries.

Fig. 1-16. Relations of the pleural cupola on the right side. Note the position of the cupola near the inferior and medial border of the scalenus anterior muscle, where it is crossed by the phrenic and vagus nerves. The subclavian artery passes anterior to the insertion of the scalenus anterior muscle on the first rib. The subclavian artery and the brachial plexus lie posterior and lateral to the muscle.

Fig. 1-17. Relations of the pleural cupola on the left side. Note the position of the cupola near the inferior and medial border of the scalenus anterior muscle. The cupola is crossed by the phrenic and vagus nerves. The vagus nerve lies between the internal jugular vein and the common carotid artery, but it is not visible in this dissection.

REFERENCES

Agostini E, Torri G: Diaphragm contraction as a limiting factor to maximum expiration. J Appl Physiol 17:427, 1962.

Brock RC: The Anatomy of the Bronchial Tree: With Special Reference to the Surgery of Lung Abscess. 2nd Ed. London: Oxford University Press, 1954.

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Campbell ETM: The role of the scalene and sternomastoid muscles in breathing in normal subjects. An electromyographic study. J Anat 89: 378, 1955.

Cherniack RM, Cherniack L: Respiration in Health and Disease. Philadelphia: WB Saunders, 1961.

Davies F, Gladstone RJ, Stibbe EP: Anatomy of intercostal nerves. J Anat 66:323, 1932.

Hughes FA: Resection of twelfth rib in surgical approach to renal fossa. J Urol 61:159, 1949.

Johnston HM: The cutaneous branches of the posterior primary divisions of the spinal nerves and their distribution in the skin. J Anat Physiol 43: 80, 1908.

Jones DS, Beargie RT, Pauly TE: Electromyographic study of some muscles of costal respiration in man. Anat Rec 117:17, 1953.

Taylor A: The contribution of the intercostal muscles to the effort of respiration in man. J Physiol (Lond) 151:390, 1960.

Trotter M: Synostosis between manubrium and body of sternum in Whites and Negroes. Am J Phys Anthropol 18:439, 1934.

READING REFERENCES

Basmajian JV: Grant's Method of Anatomy. 10th Ed. Baltimore: Williams&Wilkins, 1980.

Gardner E, et al: Anatomy. 3rd Ed. Philadelphia: WB Saunders, 1969.

Healy JE, Seybold WD: A Synopsis of Clinical Anatomy. Philadelphia: WB Saunders, 1969.

Hollinshead WH, Rosse C: Textbook of Anatomy. 4th Ed. Philadelphia: JB Lippincott, 1985.

Lachman E: Comparison of posterior boundaries of lungs and pleura as demonstrated on cadaver and on roentgenogram of the living. Anat Rec 83:521, 1942.

Mainland D, Gordon ET: Position of organs determined from thoracic radiographs of young adult males, with study of cardiac apex beat. Am J Anat 68:457, 1941.

Woodbourne RT: Essentials of Human Anatomy. 7th Ed. New York: Oxford University Press, 1983.



General Thoracic Surgery. Two Volume Set. 6th Edition
General Thoracic Surgery (General Thoracic Surgery (Shields)) [2 VOLUME SET]
ISBN: 0781779820
EAN: 2147483647
Year: 2004
Pages: 203

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