Chest wall and breast

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CHAPTER 54 Chest wall and breast

The chest wall surrounds the thoracic cavity. The skin and soft tissue cover a musculoskeletal frame consisting of 12 pairs of ribs which articulate with 12 thoracic vertebrae posteriorly, and (except for the last two pairs of ribs) with the sternum anteriorly, via their costal cartilages; intrinsic muscles and muscles which connect the chest wall with the upper limb and the vertebral column; numerous blood and lymphatic vessels and nerves which supply the components of the musculoskeletal frame and the overlying skin and breast tissue.

SKIN AND SOFT TISSUE

SKIN

Vascular supply

Arteries

The skin of the thorax is supplied by a combination of direct cutaneous vessels and musculocutaneous perforators which reach the skin primarily via the intercostal muscles, pectoralis major, latissimus dorsi and trapezius. Branches from the thoracoacromial axis, lateral thoracic artery, internal thoracic artery, anterior and posterior intercostal arteries, thoracodorsal, transverse cervical/dorsal scapular and circumflex scapular arteries are the major contributing vessels (Figs 54.1, 54.2; see Fig. 42.4).

Fig. 54.1 Anatomical territories of cutaneous blood vessels on the anterior trunk.

(By permission from Cormack GC, Lamberty BGH 1994 The Arterial Anatomy of Skin Flaps, 2nd edn. Edinburgh: Churchill Livingstone.)

Fig. 54.2 Anatomical territories of cutaneous blood vessels on the lateral trunk.

(By permission from Cormack GC, Lamberty BGH 1994 The Arterial Anatomy of Skin Flaps, 2nd edn. Edinburgh: Churchill Livingstone.)

The anterior aspect of the thoracic skin is supplied by the thoracoacromial axis, the internal thoracic arteries, perforating branches from the intercostal arteries and branches from the lateral thoracic and superficial thoracic arteries. The thoracoacromial axis supplies the skin primarily via musculocutaneous perforators from its pectoral branch, which reach the skin through pectoralis major. In addition, direct cutaneous branches arise from the acromial and deltoid branches. The internal thoracic artery sends direct perforating branches to the skin of the upper six intercostal spaces, accompanied by the cutaneous branches of the anterior intercostal nerves. The branches reach the skin after passing through pectoralis major and travelling laterally in the subcutaneous fat as direct cutaneous vessels: the second intercostal perforator is usually the largest.

The lateral aspect of the thoracic skin is supplied by the lateral thoracic, superficial thoracic and lateral cutaneous branches of the intercostal arteries. The lateral thoracic artery gives off direct cutaneous branches to the lateral chest wall in addition to musculocutaneous branches that pass through pectoralis major.

The posterior aspect of the thoracic skin is supplied by the medial and lateral dorsal cutaneous branches of the posterior intercostal arteries (which reach the skin by passing through erector spinae and latissimus dorsi), musculocutaneous perforating branches from the superficial cervical artery and the transverse cervical/dorsal scapular artery (via trapezius), musculocutaneous perforating branches from the thoracodorsal artery and the intercostal arteries (via latissimus dorsi), and direct cutaneous branches from the circumflex scapular artery.

The intercostal veins accompany the similarly named arteries in the intercostal spaces (see Fig. 53.3). The small anterior intercostal veins are tributaries of the internal thoracic and musculophrenic veins; the internal thoracic veins drain into the appropriate brachiocephalic vein. The posterior intercostal veins drain backwards and most drain directly or indirectly into the azygos vein on the right and the hemiazygos or accessory hemiazygos veins on the left. The azygos veins exhibit great variation in their origin, course, tributaries, anastomoses and termination (see Ch. 55).

Lymphatic drainage

Superficial lymphatic vessels of the thoracic wall ramify subcutaneously and converge on the axillary nodes (see p. 928, Figs 54.19, 54.21). Lymph vessels from the deeper tissues of the thoracic walls drain mainly to the parasternal, intercostal and diaphragmatic lymphatic nodes.

Fig. 54.19 The relations of the breast.

(From Drake, Vogl and Mitchell 2005.)

Fig. 54.21 Lymph vessels of the breast and the axillary lymph nodes.

Innervation

The skin of the thorax is supplied by cutaneous branches of cervical and thoracic nerves in consecutive, curved zones, the upper almost horizontal and the lower oblique. On the upper ventral thoracic aspect, the third and fourth cervical areas adjoin the first and second thoracic areas (Fig. 54.3; see Fig. 42.3) because the intervening nerves provide the sensory and motor supply to the upper limb. There is a similar, but less extensive, posterior ‘gap’: most of the skin of the back of the thorax is supplied by the dorsal rami of the thoracic nerves. The subcostal margin is supplied by the seventh thoracic nerve.

Fig. 54.3 The approximate segmental distribution of the cutaneous nerves on the front of the trunk. The contribution from the first thoracic spinal nerve is not shown and the considerable overlap that occurs between adjacent segments is not indicated.

The ventral rami of the first to the eleventh thoracic nerves pass into the intercostal spaces. Each intercostal nerve gives off a lateral cutaneous branch, which arises beyond the angle of the ribs and divides into anterior and posterior branches, and terminates near the sternum in an anterior cutaneous branch (see Fig. 54.18).

Fig. 54.18 The course of a typical intercostal nerve. The muscular and the collateral branches are not shown.

Branches of the supraclavicular nerve, which originates from the third and fourth cervical nerve roots, supply the skin in the upper pectoral region. Most of the first thoracic nerve joins the brachial plexus: it gives off a small inferior branch, which becomes the first intercostal nerve. The lateral cutaneous branch of the second intercostal nerve supplies the skin of the axilla and is known as the intercostobrachial nerve. The costal margin is supplied by a branch from the seventh thoracic nerve, and the tenth thoracic nerve supplies the skin of the abdomen at the level of the umbilicus. The seventh to eleventh thoracic nerves supply the skin of the thoracic wall as they pass anteriorly and inferiorly; they continue beyond the costal cartilages and supply the skin and subcutaneous tissues of the abdominal wall. The subcostal nerve follows the inferior border of the twelfth rib and supplies the skin of the lower abdominal wall (Fig. 54.3).

SOFT TISSUE

BONE AND CARTILAGE

The 12 thoracic vertebrae and their associated intervertebral discs are described in detail in Chapter 42.

STERNUM

The sternum consists of a cranial manubrium, an intermediate body (mesosternum) and a caudal xiphoid process (Figs 54.4, 54.5). Until puberty, the mesosternum consists of four sternebrae, which, from their costal relations, appear to be intersegmental. The total length of the sternum is approximately 17 cm in males, less in females. The ratio between manubrial and mesosternal lengths differs between the sexes. Growth may continue beyond the third decade and possibly throughout life.

Fig. 54.4 The sternum. A, Anterior aspect. B, Posterior aspect.

Part A: 1. Jugular notch. 2. Attachment for sternocleidomastoid. 3. Sternal angle and manubriosternal joint. 4. Attachment for pectoralis major. 5. Notch for seventh costal cartilage. 6. Clavicular notch. 7. Notch for first costal cartilage 8. Manubrium. 9. Notch for second costal cartilage. 10. Notch for third costal cartilage. 11. Body of sternum. 12. Notch for fourth costal cartilage. 13. Notch for sixth costal cartilage. 14. Xiphisternal joint.

Part B: 1. Jugular notch. 2. Attachment for sternohyoid. 3. Attachment for sternothyroid. 4. Edge of area covered by left pleura. 5. Edge of area covered by right pleura. 6. Attachment for transversus thoracis. 7. Area in contact with pericardium. 8. Attachment for transversus thoracis. 9. Clavicular notch. 10. Notch for first costal cartilage. 11. Manubrium. 12. Notch for second costal cartilage. 13. Sternal angle and manubriosternal joint. 14. Notch for third costal cartilage. 15. Body of sternum. 16. Notch for fourth costal cartilage. 17. Notch for fifth costal cartilage. 18. Notch for seventh costal cartilage.

Fig. 54.5 The sternum, left lateral aspect.

(From Sobotta 2006.)

In natural stance, the sternum slopes down and slightly forwards. It is convex in front, concave behind, and broadest at the junction with the first costal cartilages. It is narrow at the manubriosternal joint, below which it widens to its articulation with the fifth cartilages, and narrows again below this.

The sternum contains highly vascular trabecular bone enclosed by a compact layer that is thickest in the manubrium between the clavicular notches. Centrally, the bone is lightly constructed, whereas laterally the trabeculae are thicker and wider. The medulla contains haemopoietic bone marrow.

Manubrium

The manubrium is level with the third and fourth thoracic vertebrae. It is broad and thick above, and narrows to its junction with the body. The anterior surface is smooth, transversely convex and vertically concave, and the posterior surface is concave and smooth. The superior border is thick, and contains a central jugular (suprasternal) notch between two oval fossae, the clavicular notches, which are directed up and posterolaterally for articulation with the sternal ends of the clavicles. Fibres of the interclavicular ligament are attached to the jugular notch. The inferior border, oval and rough, carries a thin layer of cartilage for articulation with the body. The lateral borders are marked above by a depression for the first costal cartilage and below by a small articular demifacet, which articulates with part of the second costal cartilage. The narrow curved edge descends medially between these facets.

Unlike all the other sternocostal joints, the manubriocostal joint between the manubrium and the first costal cartilage is an unusual form of synarthrosis.

Body

The body is level with the fifth to ninth thoracic vertebrae. It is longer, narrower and thinner than the manubrium, and is broadest near its lower end. The anterior surface is nearly flat and faces slightly upwards. It bears three variable transverse ridges, which mark the levels of fusion of its four sternebrae. A sternal foramen, of varying size and form, may occur between the third and fourth sternebrae. The posterior surface, slightly concave, also displays three less distinct transverse lines. The oval upper end articulates with the manubrium at the level of the sternal angle (manubriosternal joint), which lies opposite the inferior border of the fourth vertebral body. The manubriosternal joint is marked by a posterior transverse groove and is palpable anteriorly as a ridge (Fig. 54.5).

The lower end of the body is narrow and continuous with the xiphoid process. On each lateral border, at its superior angle, a small notch articulates with part of the second costal cartilage (Fig. 54.4). Below this, four costal notches articulate with the third to sixth costal cartilages. The inferior angle bears a small facet which, together with the xiphoid process, articulates with the seventh costal cartilage. Between these articular depressions, a series of curved edges diminish in length downwards and form the anterior limits of the intercostal spaces.

Xiphoid process (xiphisternum)

The xiphoid process is in the epigastrium. It is the smallest and most variable sternal element, and may be broad and thin, pointed, bifid, perforated, curved or deflected. The xiphoid is cartilaginous in youth, but more or less ossified in adults. It is continuous with the lower end of the body at the xiphisternal joint. Anterior to its superolateral angles there are demifacets that articulate with parts of the seventh costal cartilages (Fig. 54.5).

Muscle attachments

The sternal ends of pectoralis major and sternocleidomastoid are attached to the anterior surface of the manubrium. Sternothyroid is attached to the posterior surface, opposite the first costal cartilage, and the most medial fibres of sternohyoid are attached above sternothyroid. The articular capsules of the sternocostal joints and sternal fibres of pectoralis major are attached to the anterior surface of the body. Transversus thoracis (sternocostalis) is attached to its posterior surface. The external intercostal membranes are attached to the borders of the body between the costal facets. The most medial fibres of rectus abdominis and the aponeuroses of external and internal oblique are attached to the anterior surface of the xiphoid. The linea alba is attached to its lower end, and the aponeuroses of internal oblique and transversus abdominis are attached to its borders. Slips of the diaphragm are attached to its posterior aspect, and the sternum is here related to the liver.

Vascular supply

The internal thoracic artery provides the main blood supply for the sternum. A sternal network of vessels derived from the internal thoracic arteries provides a network of perforating arteries at the level of each intercostal space. An anterior network formed by anastomoses between anterior superior and anterior inferior sternal branches and laterosternal and anterosternal arches provides branches that go directly into the sternum. A similar network of vessels exists posteriorly and is formed by anastomoses between posterior superior and posterior inferior vessels and laterosternal and retrosternal arches. The posterior network is more highly developed than the anterior system; these networks are particularly developed at the level of the fourth and fifth intercostal spaces.

The venous network is less developed and formed mainly by large vessels. The inframedullary network of sinuses form a network in the bone and then drain into the venous system. They are transcortical veins, and drain either into the peripheral sternal networks or into the internal thoracic vein.

Innervation

The manubrium is supplied by the anterior branch of the supraclavicular nerve and the anterior cutaneous branch of the first intercostal nerve, whereas the body of the sternum is supplied largely by anterior branches of the intercostal nerves. The anterior branch of the phrenic nerve runs anteromedially from the diaphragm and supplies the lower portion of the sternum with its contralateral counterpart.

Ossification

The sternum is formed by fusion of two cartilaginous sternal plates flanking the median plane. The arrangement and number of centres of ossification vary according to the level of completeness and time of fusion of the sternal plates, and to the width of the adult bone. Incomplete fusion leaves a sternal foramen. The manubrium is ossified from one to three centres appearing in the fifth fetal month. The first and second sternebrae usually ossify from single centres that appear at about the same time (Fig. 54.6A). Centres in the third and fourth sternebrae are commonly paired, and appear in the fifth and sixth months, respectively, but one of either pair may be delayed until the seventh or even eighth month, and the fourth sternebral centre may be absent. The xiphoid process begins to ossify in the third year or later. In some sterna, all centres are single and median; in others, the manubrial centre is single and the sternebral centres are all paired, symmetric or asymmetric. Union between mesosternal centres begins at puberty and proceeds from below upwards: by the age of 25 years, they are all united (Fig. 54.6B).

Fig. 54.6 The ossification of the sternum. A, Before birth. B, After birth.

Suprasternal ossicles, paired or single, occur sometimes. They may fuse to the manubrium or articulate posteriorly at the lateral border of the jugular notch. When well formed, they are pyramidal, and their base is articular. The ossicles are cartilaginous at birth, and ossify during adolescence.

Pectus excavatum and carinatum

Pectus excavatum occurs to some extent in about 1 in 500 live births. It is a depression of the sternum and costal cartilage that results in a funnel-shaped chest. The lower costal cartilages and the body of the sternum are depressed and there is some asymmetric curving of the ribs posteriorly. There is frequently an abnormal posture with dorsal lordosis, and some patients also develop a scoliosis. The deformity is either found at birth or occurs early in life: the majority of affected individuals show signs of the abnormality in the first 12 months of life. The aetiology is unknown, but some cases are associated with conditions such as Marfan’s syndrome, in which the connective tissue is abnormal.

Pectus carinatum is the anterior protrusion of the sternum or a pigeon chest. The deformity is less common than pectus excavatum, and although present in early childhood, it usually progresses during adolescence and then remains the same from age 18 throughout adulthood.

CLAVICLE

The clavicle is described in Chapter 46.

RIBS

The ribs are 12 pairs of elastic arches (Fig. 54.7). They articulate posteriorly with the vertebral column and form the greater part of the thoracic skeleton. Their number may be increased by cervical or lumbar ribs or reduced by the absence of the twelfth pair. The first seven pairs are connected to the sternum by costal cartilages, and are referred to as the true ribs. The remaining five are the so-called false ribs: the cartilages of the eighth to tenth usually join the superjacent costal cartilage, whereas the eleventh and twelfth ribs, which are free at their anterior ends, are sometimes termed the ‘floating’ ribs. The tenth rib may also be a floating rib; the incidence varies from 35% to 70% in different races.

Fig. 54.7 The skeleton of the thorax, anterior aspect, showing muscle attachments.

The ribs are separated by the intercostal spaces, which are deeper in front and between the upper ribs. The latter are less oblique than the lower ribs; obliquity is maximal at the ninth rib and decreases to the twelfth. Ribs increase in length from the first to seventh, and thereafter diminish to the twelfth. They decrease in breadth downwards; in the upper ten, the greatest breadth is anterior. The first two and last three ribs present special features, whereas the remainder conform to a common plan.

Ribs consist of highly vascular trabecular bone, enclosed in a thin layer of compact bone and containing large amounts of red marrow.

Typical rib

A typical rib has a shaft with anterior and posterior ends (Fig. 54.8). The anterior, costal, end has a small concave depression for the lateral end of its cartilage. The shaft has an external convexity and is grooved internally near its lower border, which is sharp, whereas its upper border is rounded. The posterior, vertebral, end has a head, neck and tubercle. The head presents two facets, separated by a transverse crest. The lower and larger facet articulates with the body of the corresponding vertebra, its crest attaching to the intervertebral disc above it. The neck is the flat part beyond the head, anterior to the corresponding transverse process. It is oblique, and faces anterosuperiorly. Its posteroinferior surface is rough and pierced by foramina. Its upper border is the sharp crest of the neck, its lower border rounded. The tubercle, which is more prominent in upper ribs, is posteroexternal at the junction of the neck and shaft and is divided into medial articular and lateral non-articular areas. The articular part bears a small, oval facet for the transverse process of the corresponding vertebra. The nonarticular area is roughened by ligaments. The shaft is thin and flat and has external and internal surfaces, and superior and inferior borders. It is curved, bent at the posterior angle (5–6 cm from the tubercle), and twisted about its long axis. The part behind the angle inclines superomedially, and so its external surface is posteroinferior. In front of the angle it faces slightly up. It is convex and smooth, and near the tubercle is crossed by a rough line, directed inferolaterally, towards the posterior angle. The smooth internal surface is marked by a costal groove, bounded below by the inferior border. The superior border of the groove continues behind the lower border of the neck, but terminates anteriorly at the junction of the middle and anterior thirds of the shaft, anterior to which the groove is absent.

Fig. 54.8 Superior surfaces of a first rib (A) and of second (B) and third (C) ribs, and the inferior surface of an eighth (D) rib, left side.

(From Sobotta 2006.)

Attachments and relations

A radiate ligament is attached along the anterior border of the head and an intra-articular ligament is attached to the crest of the head. The anterior surface of the head is related to costal pleura and, in lower ribs, to the sympathetic trunk. The anterior surface of the neck is divided by a faint transverse ridge for the internal intercostal membrane and is continuous with the inner lip of the superior border of the shaft. The area above the ridge, which is more or less triangular, is separated from the membrane by fatty tissue. The lower, smooth area is covered by costal pleura. The posterior surface of the neck gives attachment to the costotransverse ligament and is pierced by vascular foramina. The superior costotransverse ligament is attached to the crest of the neck, which extends laterally into the outer lip of the superior border of the shaft. The rounded inferior border of the neck continues laterally into the upper border of the costal groove, and gives attachment to the internal intercostal membrane. The articular area of the tubercle in the upper six ribs is convex and faces posteromedially. In the succeeding three or four ribs it is almost flat, and faces down, back and slightly medially. The lateral costotransverse ligament is attached to the non-articular area.

The ridge on the external surface of the shaft (near its posterior angle) gives attachment to an upward continuation of the thoracolumbar fascia and lateral fibres of iliocostalis thoracis. From the second to the tenth ribs, the distance between angle and tubercle increases. Medial to the angle, the external surface gives attachment to a levator costae and is covered by erector spinae. Near the sternal end of this surface an indistinct oblique line, the anterior ‘angle’, separates the attachments of external oblique and serratus anterior (or latissimus dorsi, in the case of the ninth and tenth ribs). The internal intercostal muscle is attached to the costal groove on the internal surface, and separates the bone and the intercostal neurovascular bundle. At its vertebral end, the groove faces down, its borders in the same plane. The shaft broadens near the posterior angle, and the groove reaches its internal surface. The innermost intercostal is attached to the superior rim of the groove, and this attachment occasionally extends to the anterior quarter of the rib. Posteriorly, the superior rim meets the lower border of the neck. The external intercostal muscle is attached to the sharp inferior costal border. The superior border has two lips posteriorly: an inner and an outer lip. The internal intercostal muscles and the innermost intercostal muscles are attached to the inner lip. The external intercostal muscle is attached to the outer lip.

Vascular supply and innervation

Typical ribs receive their blood supply anteriorly via branches from the internal thoracic artery (first six intercostal spaces) or musculophrenic artery (subsequent spaces), and posteriorly from intercostal arteries derived directly from the aorta. Venous drainage is into the corresponding intercostal vein and then into the azygos system. Typical ribs are innervated segmentally by branches from the corresponding intercostal nerves.

Cervical rib

A cervical rib, the costal element of the seventh cervical vertebra, may be a mere epiphysis on its transverse process, but more often it has a head, neck and tubercle. When a shaft is present, it is of variable length, and extends anterolaterally into the posterior triangle of the neck, where it may end freely or join the first rib or costal cartilage, or even the sternum. A cervical rib may be partly fibrous, but its effects are not related to the size of its osseous part. If it is long enough, its relations are those of a first thoracic rib: the brachial plexus (usually lower trunk) and subclavian vessels are superior and apt to suffer compression in a narrow angle between the rib and scalenus anterior. Hence, cervical ribs may first be revealed by nervous and vascular symptoms, particularly those caused by pressure on the eighth cervical and first thoracic spinal nerves.

A cervical rib or pleurapophysis may show synostosis or diarthrosis with either the anterior (parapophysial) or posterior (diapophysial) ‘roots’ of the so-called seventh cervical transverse process or, more usually, with both.

First rib

Most acutely curved and usually shortest, the first rib is broad and flat, its surfaces are superior and inferior, and its borders are internal and external (Fig. 54.8). It slopes obliquely down and forwards to its sternal end. The obliquity of the first ribs accounts for the appearance of pulmonary and pleural apices in the neck.

The head of the first rib is small and round. It bears an almost circular facet, and articulates with the body of the first thoracic vertebra. The neck is rounded and ascends posterolaterally. The tubercle, wide and prominent, is directed up and backwards; medially, an oval facet articulates with the transverse process of the first thoracic vertebra. At the tubercle, the rib is bent, its head turned slightly down, and so the angle and tubercle coincide. The superior surface of the flattened shaft is crossed obliquely by two shallow grooves, separated by a slight ridge, which usually ends at the internal border as a small pointed projection, the scalene tubercle, to which scalenus anterior is attached. The groove anterior to the scalene tubercle forms a bed for the subclavian vein, and the rough area between this and the first costal cartilage gives attachment to the costoclavicular ligament and, more anteriorly, to subclavius. The subclavian artery and (usually) the lower trunk of the brachial plexus pass in the groove behind the tubercle. Behind this, scalenus medius is attached as far as the costal tubercle.

The external border is convex, thick posteriorly and thin anteriorly. It is covered behind by scalenus posterior descending to the second rib. The first digitation of serratus anterior is, in part, attached to it, behind the subclavian (arterial) groove. The internal border is concave and thin, and the scalene tubercle is near its midpoint. The suprapleural membrane, which covers the cervical dome of the pleura, is attached to the internal border. The inferior surface is smooth. The anterior end is larger than in any other rib.

Vascular supply and innervation

The first rib is supplied by the internal thoracic artery and the superior intercostal artery. Venous drainage is via the intercostal vein. The rib is innervated by the first intercostal nerve.

Ossification

The first rib has a primary centre for the shaft, and secondary ossification centres for the head of the rib and the tubercle.

Second rib

The second rib is twice the length of the first rib, and has a similar curvature. The non-articular area of the tubercle is small. The angle is slight and near the tubercle. The shaft is not twisted, but at the tubercle is convex upwards, as in the first rib, but less so. The external surface of the shaft is convex and superolaterally is marked centrally by a rough, muscular impression that continues posteromedially towards the tubercle as a narrow, roughened ridge. The internal surface, smooth and concave, faces inferomedially and there is a short costal groove posteriorly.

The lower parts of the first and second digitations of serratus anterior are attached to a rough prominence that extends from just behind the midpoint of the external surface (Fig. 54.8). The distinct lips of the upper border are widely separated behind; scalenus posterior and serratus posterior superior are attached to the outer lip in front of the angle.

Vascular supply and innervation

The blood supply of the second rib is the internal thoracic artery and the superior intercostal artery. Venous drainage is via the superior intercostal vein, which drains into the brachiocephalic vein, and the anterior intercostal veins, which drain into the internal thoracic vein. The bone is innervated by branches of the first intercostal nerve.

Ossification

The second rib is ossified from a primary centre for the shaft, which appears near the angle, late in the second month. The secondary centres for the head and articular and non-articular parts of the tubercle appear about puberty, uniting to the shaft soon after the age of 20 years.

Tenth, eleventh and twelfth ribs

The tenth rib has a single facet on its head that may articulate with the intervertebral disc above, in addition to the upper border of the tenth thoracic vertebra near its pedicle. The ninth and tenth ribs are usually united anteriorly by a fibrous joint. However, the tenth rib may be free, in which case it is pointed like the eleventh and twelfth ribs.

The eleventh and twelfth ribs each have one large, articular facet on the head, but no neck or tubercle. Their pointed anterior ends are tipped with cartilage. The eleventh rib has a slight angle and shallow costal groove. The twelfth rib has neither, is much shorter and slopes cranially at its vertebral end. The internal surfaces of both ribs face slightly upwards, more so in the twelfth.

Numerous muscles and ligaments are attached to the twelfth rib (Fig. 54.9). Quadratus lumborum and its anterior covering layer of thoracolumbar fascia are attached to the lower part of its anterior surface in its medial one-half to two-thirds; the upper part is related to the costodiaphragmatic pleural recess. The internal intercostal muscle (medially) and the diaphragm (laterally) are attached at or near the upper border. The lower border gives attachment to the middle lamella of the thoracolumbar fascia and, lateral to quadratus lumborum, to the lateral arcuate ligament and posterior lamella of the thoracolumbar fascia. The lumbocostal ligament is attached posteriorly, close to the head, connecting it to the first lumbar transverse process. The lowest levator costae, longissimus thoracis and iliocostalis are attached to the medial half of the external surface, and serratus posterior inferior, latissimus dorsi and external oblique are attached to its lateral half. The external intercostal muscle is attached along the upper border. These attachments vary: those of the internal intercostal, levator costae and erector spinae merge and those of latissimus dorsi, diaphragm and external oblique may reach the costal cartilage. The lower limit of the pleural sac crosses in front of the rib, approximately at the point where it is crossed by the lateral border of iliocostalis. Its lateral end is usually below the line of costodiaphragmatic pleural reflection and is therefore not covered by pleura.

Fig. 54.9 The twelfth rib of the left side. A, Anterior aspect. B, Posterior aspect. A: 1. Attachment of internal intercostal muscle. 2. Attachment of costotransverse ligament. 3. Head. 4. Area covered by pleura. 5. Attachment of diaphragm. 6. Line of pleural reflection. 7. Attachment of quadratus lumborum. B: 1. Attachment of latissimus dorsi. 2. Attachment of external oblique. 3. Attachment of serratus posterior inferior. 4. Attachment of external intercostal muscle. 5. Attachment of levator costae. 6. Head. 7. Attachment of erector spinae.

Vascular supply and innervation

The tenth and eleventh ribs are supplied by the posterior intercostal artery and branches from the musculophrenic artery. The twelfth rib is supplied by the subcostal artery. Venous drainage is via the posterior intercostal and subcostal veins, which in turn drain into the azygos system. There is additional drainage via the anterior intercostal veins (branches of the musculophrenic vein). The tenth and eleventh ribs are innervated by the corresponding intercostal nerve, and the twelfth rib is innervated by the subcostal nerve.

Ossification

The tenth rib ossifies from a primary centre in the shaft and secondary centres for the head and articular parts of the tubercle. The eleventh and twelfth ribs, without tubercles, have two centres each.

Costal cartilages

Costal cartilages are the persistent, unossified anterior parts of the cartilaginous models in which the ribs develop. They are flat bars of hyaline cartilage that extend from the anterior ends of the ribs, and contribute greatly to thoracic mobility and elasticity (Fig. 54.7). The upper seven pairs join the sternum; the eighth to tenth articulate with the lower border of the cartilage above; the lowest two have free, pointed ends in the abdominal wall. They increase in length from the first to the seventh, and then decrease to the twelfth. They diminish in breadth from first to last, like the intercostal spaces. The costal cartilages are broad at their costal continuity and taper as they pass forward. The first and second are of even breadth and the sixth to eighth enlarge where their margins are in contact. The first descends a little, the second is horizontal and the third ascends slightly; the others are angulated and incline up towards the sternum or cartilage above, a little anterior to their ribs.

Each costal cartilage has two surfaces, borders and ends. The anterior surface is convex, facing anterosuperiorly. The sternoclavicular articular disc, costoclavicular ligament and subclavius are attached to the first costal cartilage. Pectoralis major is attached to the medial aspect of the first six cartilages and the others are covered by the partial attachments of the anterior abdominal muscles. The posterior surface is concave, and really posteroinferior. Sternothyroid is attached to the first cartilage, transversus thoracis is attached to the second to sixth, and transversus abdominis is attached to the lower six. The internal intercostal muscles and external intercostal membranes are attached to the concave superior and convex inferior borders. The inferior borders of the fifth (sometimes), and sixth to ninth cartilages project at points of greatest convexity. Oblong facets on these projections articulate with facets on slight projections from the superior borders of subjacent cartilages. The lateral end of each cartilage is continuous with its rib. The medial end of the first is continuous with the sternum; those of the six succeeding cartilages are round and articulate with shallow costal notches on the lateral margins of the sternum; those of the eighth to tenth are pointed, each connected with the cartilage above; those of the eleventh and twelfth are pointed and free. With the exception of the synarthrosis between the first rib and sternum, all these articulations are synovial.

In old age the costal cartilages tend to ossify superficially, lose their pliability and become brittle.

Rib fractures

Elastic recoil of the ribs which suspend the sternum may explain the rarity of sternal fractures. Despite their pliability, the ribs are much more frequently broken, the middle ribs being the most vulnerable. Because traumatic stress is often the result of compression of the thorax, the usual site of fracture is just in front of the angle, which is the weakest point of the rib. Direct impact may fracture a rib at any point; the ends of the broken bone may be driven inwards, and potentially may injure thoracic or upper abdominal viscera.

JOINTS

MANUBRIOSTERNAL JOINT

The manubriosternal joint lies between the manubrium and sternal body, and is usually a symphysis. The bony surfaces are covered by hyaline cartilage and connected by a fibrocartilage, which may ossify in the aged. Sometimes, the central part of the disc is absorbed and the joint appears synovial. The manubriosternal joint is connected by a fibrous membrane enveloping the entire bone. In occasional individuals over the age of 30 years, the manubrium is joined to the sternal body by bone, but the intervening cartilage may be only superficially ossified; ossification becomes complete only in the aged. Early synostosis has been attributed to a persistent synchondrosis in place of a symphysis. In the newborn, union is by collagenous and elastic fibres, without chondrocytes.

Movements

The symphysis permits a small range of angulation between the longitudinal axes of the manubrium and body of the sternum, and also limited anteroposterior displacement. A study of these movements in 62 male athletes yielded (standing position) mean values of 162.7° (full inspiration) and 164.7° (full expiration) for the manubriosternal angle: both movements contribute to respiratory excursions of the sternum.

Heads of typical ribs articulate with facets (often termed demifacets) on the margins of adjacent thoracic vertebral bodies and with the intervertebral discs between them (Fig. 54.10). The first and tenth to twelfth ribs articulate with a single vertebra by a simple synovial joint. In the others, an intra-articular ligament bisects the joint, producing a double synovial compartment, so the joint is classified as both compound and complex. Often inaccurately described as plane, their articular surfaces are slightly ovoid and the upper and lower synovial articulations are obtusely angled to each other. The ligaments are capsular, radiate and intra-articular.

Fig. 54.10 Ligaments of the vertebral column and costovertebral joints, lateral parts of the anterior longitudinal ligament removed, left lateral aspect.

(From Sobotta 2006.)

Fibrous capsules

The fibrous capsule connects the costal head to the circumference of the articular surface formed by an intervertebral disc and the demifacets of two adjacent vertebrae. Some of the upper fibres traverse their intervertebral foramina to blend with the posterior aspects of the intervertebral discs; the posterior fibres are continuous with the costotransverse ligaments.

Radiate ligaments

Radiate ligaments connect the anterior parts of each costal head to the bodies of two vertebrae and their intervening intervertebral disc. Each is attached to the head just beyond its articular surface. Superior fibres ascend to the vertebral body above, inferior to the body below. Intermediate fibres, shortest and least distinct, are horizontal and attached to the disc. The radiate ligament associated with the first rib is attached to the seventh cervical and first thoracic vertebrae. In the joints of the tenth to twelfth ribs, which articulate with single vertebrae, the radiate ligament is attached to the numbered vertebra and the one above.

Intra-articular ligament

The intra-articular ligament is a short, flat band, attached laterally to the crest between the costal articular facets and medially to the intervertebral disc, dividing the joint. The ligament is absent from the first and tenth to twelfth joints.

Costotransverse joints

The facet of a costal tubercle articulates reciprocally with the transverse process of its corresponding vertebra (Fig. 54.11). The eleventh and twelfth ribs lack this articulation. In the upper five or six joints, articular surfaces are reciprocally curved, but below this they are flatter (Fig. 54.12). Their ligaments are capsular, costotransverse, superior and lateral costotransverse, and accessory.