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.)
Veins
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.
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.
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).
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.
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).
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).
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.
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.
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.
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.
Second rib
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.
Tenth, eleventh and twelfth ribs
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.
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.
JOINTS
COSTOVERTEBRAL, STERNOCOSTAL AND INTERCHONDRAL JOINTS
Joints of costal heads
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.
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.
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.
