Physical Address
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Chest wall and breast
The chest wall surrounds the thoracic cavity. It is formed by: an osseocartilaginous frame consisting normally of 12 pairs of ribs, which articulate with the 12 thoracic vertebrae posteriorly and (except for the last two or three pairs of ribs) with the sternum anteriorly, via their costal cartilages; intrinsic muscles and muscles that connect the chest wall with the upper limb and the vertebral column; overlying skin, fasciae and breast tissue; and numerous blood and lymphatic vessels and nerves that supply the components of the musculoskeletal frame.
Skin and Fascia
Skin
Vascular supply
Arteries
The skin of the thorax is supplied by a combination of direct cutaneous vessels and musculocutaneous perforators that reach the skin primarily via the intercostal muscles, pectoralis major, latissimus dorsi and trapezius. The major contributing vessels are branches from the thoraco-acromial, lateral thoracic, superficial thoracic and internal thoracic, anterior and posterior intercostal, thoracodorsal, transverse cervical, dorsal scapular and circumflex scapular arteries ( Figs 53.1 – 53.2 ; see Fig. 46.4 ).
The anterior aspect of the thoracic skin is supplied by branches of the thoraco-acromial artery, the internal thoracic arteries, perforating branches from the intercostal arteries and branches from the lateral thoracic and superficial thoracic arteries. The thoraco-acromial artery supplies the skin primarily via musculocutaneous perforators from its pectoral branch that reach the skin through pectoralis major. Direct cutaneous branches also arise from the acromial and deltoid branches. The internal thoracic artery sends direct perforating branches to the skin covering the first (superior) six intercostal spaces and associated costal cartilages, 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 right internal thoracic artery is normally larger than the left and the perforator in the second intercostal space is usually the largest. The lateral aspect of the thoracic skin is supplied by the lateral thoracic and superficial thoracic arteries, lateral cutaneous branches of the intercostal arteries, and musculocutaneous branches of the thoracodorsal artery (via latissimus dorsi). 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 (via erector spinae and latissimus dorsi) (see Fig. 53.18 ); musculocutaneous perforating branches from the superficial cervical, transverse cervical and dorsal scapular arteries (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.
Veins
The intercostal veins accompany the similarly named arteries in the intercostal spaces (see Fig. 52.4 ). The small anterior intercostal veins are tributaries of the musculophrenic and internal thoracic veins, the latter draining into the ipsilateral brachiocephalic vein. The posterior intercostal veins 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 ( Ch. 56 ).
Lymphatic drainage
Superficial lymphatic vessels of the thoracic wall ramify subcutaneously and converge on the axillary nodes (see Figs 53.22 , 53.24 , 46.5 and Ch. 49 ). Lymph vessels from the deeper tissues of the thoracic walls drain mainly to the parasternal, intercostal and diaphragmatic lymph nodes.
Innervation
The skin of the thorax is supplied by cutaneous branches of cervical and thoracic spinal nerves in consecutive overlapping curved zones; the upper zones are almost horizontal and the lower curve obliquely inferiorly around the thoracic wall as they pass to the anterior midline (median plane). On the upper anterior aspect of the thorax, the areas innervated by the ventral rami of the third and fourth cervical nerves adjoin those innervated by the ventral rami of the second (and sometimes first) thoracic spinal nerves because the intervening thoracic spinal nerves are distributed to the upper limb ( ) ( Fig. 53.3 ). There is a similar but less extensive ‘gap’ in innervation on the upper posterior thoracic wall (see Fig. 47.8 ). Most of the skin covering the posterior thorax is supplied by the dorsal rami of the thoracic spinal nerves.
The ventral rami of the first to the eleventh thoracic spinal nerves pass into the correspondingly numbered intercostal space, give off a lateral cutaneous branch distal to the angle of the rib (that then divides into anterior and posterior rami) and terminate near the sternum as an anterior cutaneous branch (that divides into medial and lateral branches) (see Fig. 53.21 ).
Branches of the supraclavicular nerves, which originate from the ventral rami of the third and fourth cervical spinal nerves, supply the skin in the upper pectoral region. Most of the ventral ramus of the first thoracic spinal nerve joins the brachial plexus, apart from a small inferior branch that becomes the first intercostal nerve. The lateral cutaneous branch of the second intercostal nerve (intercostobrachial nerve) supplies the skin of the axilla, lateral chest and medial arm. It courses as either a single trunk or in a bifurcating pattern ( ): its variability puts it at increased risk of injury during breast-related surgery, potentially resulting in postoperative pain and paraesthesia. The ventral rami of the seventh to eleventh thoracic spinal nerves supply the skin of the thoracic wall as they pass anteriorly and inferiorly; they continue beyond the costal cartilages to supply the skin and subcutaneous tissues of the abdominal wall (see Fig. 60.5 ). The skin of the abdomen at the level of the umbilicus is supplied by the ventral ramus of the tenth thoracic spinal nerve. The subcostal nerve (ventral ramus of twelfth thoracic spinal nerve) follows the inferior border of the twelfth rib and supplies the skin of the lower abdominal wall.
Fascia
Superficial fascia
The superficial fascia consists primarily of fat and is only loosely attached to the skin, an arrangement that allows movement of the underlying structures. Small blood vessels and nerves perforate the superficial fascia to supply the skin. The breast lies within the superficial fascia, apart from a superolateral extension that pierces the deep fascia to form the axillary process (tail, tail of Spence) in the female.
Deep fascia
Clavipectoral fascia
The clavipectoral fascia is the cranial continuation of the deep lamina of the pectoral fascia and the medial continuation of the parietal layer of the subscapular bursal fascia. It extends between the clavicle and pectoralis minor, surrounds subclavius and extends medially to the first rib. It is described in detail in Chapter 49 .
Bone and Cartilage
The 12 thoracic vertebrae and associated intervertebral discs are described in detail in Chapter 46 .
Sternum
The sternum is an elongated, flattened bone that forms the middle portion of the anterior thoracic wall. It consists of three parts, namely (from cranial to caudal): manubrium, body and xiphoid process ( Figs 53.4 – 53.5 ) and articulates with the clavicles at the sternoclavicular joints and with the cartilages of the first seven pairs of ribs at the costosternal joints. Until puberty, the body consists of four intersegmental sternebrae. The average length of the adult sternum is 16.5 cm in males and 15.0 cm in females: the ratio between the length of the sternal manubrium and body differs between males and females. Sternal growth may continue beyond the third decade and possibly throughout life.
The sternum projects (slopes) anteroinferiorly from the jugular notch. Viewed as a whole, and due to the angulation of the manubriosternal joint, the majority of the anterior surface of the sternum appears vertically convex and the posterior surface appears vertically concave. Inferiorly and proximal to the xiphoid process, the shape transitions to become vertically concave on both anterior and posterior surfaces. The geometry of the individual parts of the sternum vary with surface and region ( , ). The manubrium is the broadest part, at its joints (articulations) with the first costal cartilages. It narrows at the manubriosternal joint, gradually widens to its joints with the fifth costal cartilages, and then narrows to the xiphoid process. 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 relatively lightly constructed; the trabeculae are thicker and wider laterally. The medullary cavity contains haematopoietic bone marrow. The sternum and its component parts may be variable in morphology, joint alignment and fusion, and can contain clefts or foramen ( ).
Manubrium of sternum
The jugular notch (superior border) of the manubrium of the sternum commonly aligns with the bodies of the second to third thoracic vertebrae, and the inferior border with the bodies of the fourth to fifth thoracic vertebrae at the manubriosternal joint. It has an average length of 5.1 cm and forms up to 35% of the total sternal length. It has a somewhat quadrangular shape, being broad and thick superiorly and narrowing inferiorly to its junction with the sternal body. The anterior and posterior surfaces are smooth in appearance. The anterior surface is transversely convex and vertically concave in shape, whereas the posterior surface is both transversely and vertically concave. The superior border is thick in the sagittal plane and bears the jugular (suprasternal) notch in the midline between the left and right clavicular notches. The clavicular notches are directed superiorly, posteriorly and laterally for articulation with the sternal articular surface of the clavicles. Fibres of the interclavicular ligament attach to the jugular notch. The inferior border is oval and rough and carries a thin layer of hyaline cartilage for articulation with the sternal body. The lateral borders are marked at the widest part of the manubrium by a depression for the first costal cartilage (first costal notch), and, inferior to this depression, by a small articular demifacet that articulates with part of the second costal cartilage. The narrow curved lateral border descends medially between these facets. There is little accessory movement at the manubriosternal joint, although pressure on either the sternal body or manubrium close to the joint will produce slight angling of the two sections, particularly in younger individuals.
Unlike all the other sternocostal joints, the joint between the manubrium and the first costal cartilage is a fibrous synarthrosis. It lies about 1 cm below and 1 cm lateral to the sternal (medial) end of the clavicle and is difficult to palpate.
Body of sternum
The body of the sternum is located level with the bodies of the fourth or fifth to the ninth thoracic vertebrae. It is longer, narrower and thinner than the manubrium, and is broadest at its junction with the fifth costal cartilages. The anterior surface is vertically convex and transversely varies from convex to concave depending upon region. It faces slightly superiorly and usually bears three variable transverse ridges that mark the levels of fusion of its four sternebrae (see Fig. 53.6B ). Sternal foramina, of varying size, form and completeness, may occur in up to 10% of the population in the body of the sternum ( ). The posterior surface is vertically concave and transversely convex in shape and bears three transverse lines. The oval superior border articulates with the inferior border of the manubrium at the level of the manubriosternal joint (sternal angle) that commonly lies horizontally level with the inferior border of the body of the fourth thoracic vertebra, T4–T5 intervertebral disc or body of the fifth thoracic vertebra (the sternal plane), and is marked anteriorly and posteriorly by a transverse ridge and groove, respectively.
On each lateral border, at its superior angle and lateral to the manubriosternal joint, a small notch articulates with part of the second costal cartilage (see Figs 53.4 – 53.5 ). Inferiorly, 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 are a series of curved bony edges that form the anterior limits of the associated intercostal spaces. The sternal body narrows from the fifth costal notch inferiorly to the xiphisternal joint, where it articulates with the xiphoid process.
Xiphoid process (xiphisternum)
The xiphoid process joins the inferior part of the sternal body at the xiphisternal joint, commonly level with the body of the ninth thoracic vertebra. It is the smallest and most variable part of the sternum, and may be broad and thin, pointed, bifid, triangular, perforated or curved (see Fig. 53.8 ). It sits in the epigastric region of the abdomen, therefore when elongated and curved anteriorly it may be mistaken for an epigastric mass, and when unusually long with a sharp bifid end it can damage the liver. The xiphoid process is cartilaginous during early life and is commonly ossified in adults. Costal notches located on the superolateral border, lateral to the xiphisternal joint, articulate with part of the seventh costal cartilages (see Fig. 53.5 ).
Muscle attachments
The sternocostal head of pectoralis major and sternal head of sternocleidomastoid are attached to the anterior surface of the manubrium (see Fig. 53.4 ). Sternothyroid is attached to the posterior surface of the manubrium, opposite or just inferior to the first costal notch, and the most medial fibres of sternohyoid are attached superior to sternothyroid and level with the clavicular notch. The articular capsules of the sternocostal joints and sternocostal fibres of pectoralis major are attached to the anterior surface of the body of the sternum, and transversus thoracis (sternocostalis) is attached to the posterior surface. The external intercostal membranes are attached to the lateral borders of the body of the sternum between the costal notches. The most medial fibres of rectus abdominis and the aponeuroses of external and internal abdominal oblique are attached to the anterior surface of the xiphoid process. The linea alba is attached to its inferior end, and the aponeuroses of internal abdominal oblique and transversus abdominis are attached to its non-articular borders. Slips of the respiratory diaphragm are attached to its posterior surface, and posteriorly it is related to the liver.
Vascular supply
The internal thoracic artery provides the main blood supply for the sternum via anterior and posterior networks of perforating arteries that directly penetrate the sternum at the level of each intercostal space. These networks are particularly well developed posteriorly and at the level of the fourth and fifth intercostal spaces.
The venous network is less developed. It is formed mainly by an inframedullary network of sinuses in the bone that drain via transcortical veins either into the peripheral sternal networks or the internal thoracic vein.
Innervation
The manubrium is innervated 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 innervated largely by anterior branches of the second to sixth intercostal nerves. The anterior (sternal) branch of the phrenic nerve arises within or immediately inferior to respiratory diaphragm and runs anteromedially to innervate the lower part of the body of the sternum and xiphoid process.
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 according to the final width of the adult bone. Incomplete fusion leaves a sternal foramen ( ). The manubrium is ossified from one to three centres that appear during postmenstrual weeks 17–20. The sternal body is formed from four sternebrae. The first and second sternebrae usually ossify from single centres that appear at about the same time ( Fig. 53.6A ). Centres in the third and fourth sternebrae are commonly paired, and appear during postmenstrual weeks 17–20 and 21–24, respectively; one of either pair may be delayed until after postmenstrual week 28, and the fourth sternebral centre may be absent. The xiphoid process begins to ossify in the third year or even later. In some sterna, all centres are single and median; in others, the manubrial centre is single and the sternebral centres are paired, symmetric or asymmetric. Union between the sternebral centres begins at puberty and proceeds from inferior to superior; by 25 years of age, they are all united ( Fig. 53.6B ).
Suprasternal ossicles, paired or single, sometimes occur. They may fuse to the manubrium or articulate posteriorly at the lateral border of the jugular notch. When well formed, they are pyramidal with an articular base. The ossicles are cartilaginous at birth and ossify during adolescence.
Pectus excavatum and carinatum
Pectus excavatum is the most common congenital deformity of the anterior thoracic wall and is more common in males than females. It is a depression of the sternum and costal cartilage that is sometimes referred to as cobbler’s chest, sunken chest, the crevasse or funnel chest. The lower (inferior) costal cartilages and the body of the sternum are depressed and there is some asymmetric curving of the ribs posteriorly. There is often an abnormal posture with dorsal lordosis, sometimes with developing scoliosis. The deformity is found either at birth (1 in 400 live births) or early in life; in the majority of cases, the condition is visible by 1 year of age but may not develop until puberty. The aetiology is unknown but some cases are associated with connective tissue diseases, such as Marfan syndrome.
The clinical significance of pectus excavatum may vary considerably ( Fig. 53.7 ). Severe defects can lead to cardiopulmonary dysfunction, including changes in cardiac anatomy due to compression of the right ventricle and left atrium between the sternum and thoracic vertebral column. Almost all patients will have some degree of cosmetic concern, while back and chest pain may occur. Evaluation of the deformity demands careful symptom assessment in addition to baseline radiological investigations (chest radiograph and computed tomography (CT)). Where there are physiological restrictions, lung function tests, electrocardiograms (ECGs), echocardiograms and MR-based strain imaging form part of the assessment before specialist clinicians can determine the safety of surgical intervention ( ). A classification system based on morphology using CT scanning has been proposed ( ) and is useful for standardizing the results of surgical correction of the different subtypes.
Mild defects causing aesthetic concerns may be improved with customized silicone implants ( ) or with soft tissue reconstructive procedures ( ), to camouflage the concavity. More severe defects often require correction of the underlying skeletal deformity. Several techniques have been described. Open resection procedures were pioneered by Ravitch in the 1950s and subsequently minimally invasive techniques have gained in popularity ( , ). With the development of three-dimensional (3D) printers, simulated surgeries can now be performed using patient-specific 3D chest wall models, allowing higher precision in bar placement and the number required for the best surgical outcome ( ). Additionally, 3D printing of titanium plate and polyethylene implants has allowed for advances in patient implant customization and an increase in optimal surgical outcomes ( ).
Pectus carinatum, often called ‘pigeon chest’, is an overgrowth of cartilage that causes the sternum to protrude forwards. It is less common than pectus excavatum, accounting for 5–20% of anterior thoracic wall deformities: a quarter of cases are familial. The condition may occur as a solitary congenital anomaly or in association with other genetic disorders. Although present in early childhood, pectus carinatum usually progresses during adolescence and then remains unchanged throughout adulthood. In recent years treatment has gravitated towards minimally invasive or noninvasive methods of applying external pressure to the anterior chest wall to depress the sternum ( ). Pectus carinatum occurs in three different ways, most commonly in pubertal males aged 11–14 years undergoing a growth spurt. Some parents report that their child’s pectus seemingly popped up ‘overnight’. The second most common occurrence is from birth, when it is evident in newborns as a rounded chest, becoming more prominent as the child reaches 2 or 3 years old. The least common occurrence is as an acquired condition after open heart surgery, when healing has been aberrant. Pectus carinatum may be associated with Turner, Marfan, Ehlers–Danlos, Morquio’s, Noonan’s, Sly’s or multiple lentigines syndromes, trisomies 18 or 21, homocystinuria, osteogenesis imperfecta or scoliosis.
Clavicle
The clavicle is described in Chapter 49 .
Ribs
The ribs are 12 pairs of curved bony arches with elastic properties (as measured by their stress–strain relationship) ( Fig. 53.8 ). Each consists of a highly vascular trabecular bone containing large amounts of red marrow, enclosed in a thin layer of compact bone. The ribs articulate posteriorly with the thoracic 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 ‘true’ ribs connect directly to the costal notches of the sternum by costal cartilages, whilst the remaining inferior five ‘false’ ribs either join the costal cartilage (ribs 8–10) located immediately superior, or ‘float’ free at their anterior ends as relatively small and delicate structures tipped with cartilage (ribs 11 and 12). The tenth rib may also float; the incidence varies from 35% to 70%, depending on ancestry. The ribs change in their width, height and angulation with growth and/or age ( , , ).
The ribs are separated by the intercostal spaces, which are deeper anteriorly and between the more superiorly located ribs. The latter are less oblique than the inferiorly located ribs; obliquity is maximal at the ninth rib. The ribs increase in length up to the seventh and thereafter decrease in length. In general, they decrease in height or breadth from superior to inferior; the upper ten are at their highest/broadest at their anterior ends. The first two and the last three ribs have special features, whereas the remainder show a typical form.
Typical rib
A typical rib has a shaft with anterior and posterior ends ( Fig. 53.9 ). The anterior costal end has a small concave depression for articulation with the lateral end of its cartilage. The shaft has an external convexity and is grooved internally near its inferior border, which is sharp, whereas its superior border is rounded. The posterior vertebral end has a head, neck and tubercle. The head presents two articular facets, separated by a transversely oriented crest. The inferior and larger facet articulates with the body of the correspondingly numbered vertebra, its crest attaches to the superiorly located intervertebral disc and the smaller superior facet articulates with the body of the vertebra above. The neck is the flat part distal to the head and anterior to the transverse process of the correspondingly numbered thoracic vertebra. It is oblique and faces anterosuperiorly. Its posteroinferior surface is rough and pierced by foramina. Its superior border is sharp and formed by the crest of the neck, and its inferior border is rounded. The tubercle is located posteriorly between the neck and angle of the rib and is more prominent in the superiorly located ribs. It is divided into a medial articular area that bears a small oval facet for the transverse process of the correspondingly numbered thoracic vertebra, and a roughened lateral non-articular area for ligamentous attachment. The shaft is thin and flat, with external and internal surfaces, and superior and inferior borders. It is curved, bent at the angle of the rib, about 5–6 cm lateral to the tubercle, and twisted about its long axis. The smooth internal surface of the rib is marked by the costal groove, bounded inferiorly by the inferior border and which houses the intercostal neurovascular bundle (see Fig. 53.17 ). The superior border of the costal groove continues posteriorly as the inferior border of the neck of the rib, but terminates anteriorly at the junction of the middle and anterior thirds of the shaft: the groove is often absent anterior to this junction
Attachments and relations
A radiate ligament is attached along the anterior border of the head of the rib and an intra-articular ligament is attached along its crest (see Fig. 53.11 ). The anterior surface of the head is related to costal parietal pleura and, in the more inferior ribs, to the sympathetic trunk and ganglia. The anterior surface of the neck of the rib is divided by a faint transverse ridge, for attachment of the internal intercostal membrane, and is continuous with the inner lip of the superior border of the shaft. The area superior to the ridge, which is more or less triangular, is separated from the membrane by fatty tissue and the area inferior to the ridge is smooth and covered by costal parietal pleura. The posterior surface of the neck gives attachment to the costotransverse ligament and contains vascular foramina. The superior costotransverse ligament is attached to the crest on the neck of the rib that extends laterally into the outer lip of the superior border of the shaft. The rounded inferior border of the neck of the rib continues laterally into the superior border of the costal groove, and gives attachment to the internal intercostal membrane. The articular facet on the tubercles of the first to the sixth ribs is convex and faces posteromedially. In the subsequent three or four ribs it is almost flat, and faces inferiorly, posteriorly and slightly medially. The lateral costotransverse ligament is attached to the non-articular area.
The ridge on the external surface of the shaft (near to the angle of the rib) 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 of the rib increases. Medial to the angle, the external surface gives attachment to levator costae and is covered by erector spinae. Near the sternal end of this surface, an indistinct oblique line, the anterior ‘angle’ of the rib, separates the attachments of external abdominal 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 intercostal neurovascular bundle from the bone of the rib. At its vertebral end, the costal groove faces inferiorly. The shaft of the rib broadens posteriorly near the angle, and the costal groove reaches its internal surface. The innermost intercostal muscle is attached to the superior border of the costal groove; this attachment occasionally extends to the anterior quarter of the rib. The external intercostal muscle is attached to the sharp inferior border of the rib. The superior border of the rib 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 and 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 posterior intercostal arteries derived directly from the descending thoracic aorta. Venous drainage is into the corresponding intercostal vein and subsequently into the azygos system or the brachiocephalic vein (see Fig. 52.4 ). Typical ribs are innervated segmentally by branches from their corresponding intercostal nerves.
Variant and accessory ribs
Ribs may be asymmetric, absent, fused, intrathoracic or accessory ( ). Accessory (supernumerary) ribs may be in a cervical or lumbar location, lumbar being the most common but least problematic.
Cervical ribs arise from the seventh cervical vertebra, occur in up to 1% of the population, and are thought to result from mutations of HOX genes ( ). Their size varies from a simple epiphysis on the transverse process of the seventh cervical vertebra to, more commonly, a structure with 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 its costal cartilage, or even the manubrium of the sternum. Long cervical ribs have relations similar to those of the first thoracic rib: the brachial plexus (usually lower trunk) and subclavian vessels are superior and may become compressed in the narrow angle between the rib and scalenus anterior. This anatomical relationship means that cervical ribs may first be revealed by neurovascular symptoms (thoracic outlet syndrome, see Ch. 48 ) including ipsilateral limb pain, numbness, weakness or cold intolerance, particularly when the cervical rib puts pressure on the ventral rami of the eighth cervical and first thoracic spinal nerves. The symptoms resulting from a cervical rib are unrelated to the relative sizes of its constituent parts (specifically osseous vs fibrous). A cervical rib (pleurapophysis) may show synostosis or diarthrosis with either the anterior (parapophysial) or posterior (diapophysial) ‘roots’ of the transverse process of the seventh cervical vertebra or, more usually, with both.
First rib
The first rib is broad and flat, has superior and inferior surfaces and internal and external borders, and is the most acutely curved and shortest of all the ribs (see Fig. 53.9 ). It slopes obliquely anteroinferiorly towards its sternal end, which is larger than that of any other rib. The obliquity of the first rib means that the lung apex and covering pleura project superior to the superior thoracic aperture and into the neck.
The head of the first rib is small and round, bears an almost circular facet that articulates with the body of the first thoracic vertebra, and is turned slightly inferiorly relative to the tubercle of the rib. The neck of the rib is rounded and ascends posterolaterally, and the tubercle is wide and prominent and directed superiorly and posteriorly. Medially, an oval facet articulates with the transverse process of the first thoracic vertebra. The angle and tubercle of the first rib normally coincide. The inferior surface of the flattened shaft of the rib is smooth whereas the superior surface is crossed obliquely by two shallow grooves, separated by a slight ridge that usually terminates at the scalene tubercle (a small pointed projection located on the internal border of the rib 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, even more anteriorly, to subclavius (see Fig. 53.8 ). The subclavian artery and (usually) the lower trunk of the brachial plexus pass in the groove posterior to the scalene tubercle. Posterior to the scalene tubercle, scalenus medius is attached as far as the tubercle/angle of the rib.
The superior half of the smooth inferior surface is covered by endothoracic fascia and costal parietal pleura, the inferior half is an attachment point for the intercostal muscles and membranes. The external border is convex, thick posteriorly and thin anteriorly. It is covered posteriorly by scalenus posterior descending to the second rib. The first digitation of serratus anterior is, in part, attached to it, lateral to the groove for the subclavian vein. The internal border is concave and thin, and the scalene tubercle is near its midpoint. The suprapleural membrane (Sibson’s fascia), covering the cervical parietal pleura and lung apex, is attached to the internal border ( Ch. 54 ).
Vascular supply and innervation
The first rib is supplied by the internal thoracic and supreme intercostal arteries, drained by the supreme intercostal vein and innervated by the first intercostal nerve.
Ossification
The first rib has a primary ossification centre for the shaft, and secondary ossification centres for the head of the rib and the tubercle.
Second rib
The second rib is about twice the length of the first and has a similar curvature. The non-articular area of its tubercle is small. The angle of the rib is small and near the tubercle. The shaft is not twisted but at the tubercle is superiorly convex. The external surface of the shaft is convex and at around the midpoint is marked by a raised roughened prominence for the attachments of the inferior halves of the first and the second digitation of serratus anterior (see Figs 53.8 – 53.9 ). Passing anteriorly from the angle of the rib, a distinct midline ridge divides the external (upper) surface into outer and inner parts: scalenus posterior and serratus posterior superior are attached to the ridge and to the outer part. The internal surface of the shaft is smooth and concave, faces inferomedially and has a relatively short costal groove along the posterior part of its inferior border. The superior half of the internal surface is covered by endothoracic fascia and costal parietal pleura, and the inferior half is an attachment point for the intercostal muscles and membranes.
Vascular supply and innervation
The second rib is supplied by the internal thoracic and supreme intercostal arteries, drained via the superior intercostal vein into the brachiocephalic vein, and by the anterior intercostal veins into the internal thoracic vein, and innervated by branches of the second intercostal nerve.
Ossification
The second rib is ossified from a primary ossification centre for the shaft, which appears near the angle late in postmenstrual weeks 5–8. The secondary centres for the head and articular and non-articular parts of the tubercle appear around 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 articulates with the superior border of the body of the tenth thoracic vertebra near the pedicle, and may also articulate with the T9–T10 intervertebral disc. The costal cartilages of the ninth and tenth ribs may be united anteriorly by a fibrous joint, although in up to 70% of subjects the tenth rib may be free, in which case its end appears pointed like the eleventh and twelfth ribs.
The eleventh and twelfth ribs each have one large articular facet on their heads but no necks or tubercles. Their anterior ends are pointed and tipped with hyaline cartilage. The eleventh rib has a slight angle and shallow costal groove whereas the twelfth rib has neither, is much shorter and slopes cranially at its vertebral end. The internal surfaces of both ribs face slightly superiorly, this being more apparent in the twelfth.
Numerous muscles and ligaments are attached to the twelfth rib (see Fig 53.8 ; Fig. 53.10 ). Quadratus lumborum and its anterior covering layer of thoracolumbar fascia are attached to the medial one-half to two-thirds of the inferior part of the anterior surface. The medial half of the internal surface is related to the costodiaphragmatic recess of the pleural cavity, approximately at the point where it is crossed by the lateral border of iliocostalis: the recess may extend inferior to the rib. The internal intercostal muscle (medially) and the respiratory diaphragm (laterally) are attached at or near the superior border. The inferior border and associated external surface give attachment to the middle layer of the thoracolumbar fascia and, lateral to quadratus lumborum, to the lateral arcuate ligament and posterior layer of the thoracolumbar fascia. The lumbocostal ligament is attached posteriorly, posterior to quadratus lumborum and normally close to the head of the twelfth rib (although it may extend more laterally): distally, the ligament is attached to the transverse processes of the first and second lumbar vertebrae and can be used to locate the subcostal nerve ( ). The lowest levator costae, longissimus thoracis and iliocostalis are all attached to the medial half of the external surface; serratus posterior inferior, latissimus dorsi and external abdominal oblique are attached to the lateral half of the external surface; the external intercostal muscle is attached along the central section of the superior part of the external surface. These attachments can vary; in particular, the attachments of the internal intercostal, levator costae and erector spinae merge and those of latissimus dorsi, the respiratory diaphragm and external abdominal oblique may reach the costal cartilage.
Vascular supply and innervation
The tenth and eleventh ribs are supplied by the posterior intercostal arteries and by branches from the musculophrenic artery. The twelfth rib is supplied by the subcostal artery. Venous drainage is via the posterior intercostal and subcostal veins that drain into the azygos system and 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 ossification centre in the shaft and secondary centres for the head and articular parts of the tubercle. The eleventh and twelfth ribs, without tubercles, both have two ossification centres.
Costal cartilages
The costal cartilages are the unossified anterior parts of the cartilaginous models from 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 (see Fig. 53.8 ). The upper seven pairs articulate with the sternum; the eighth to tenth articulate with the inferior border of the costal cartilage above; and the lowest two have free, pointed ends located within the soft tissue of the abdominal wall (see Figs 53.14 , 53.15B ). The costal cartilages increase in length from the first to the seventh, and then decrease to the twelfth. They diminish in breadth/height from first to last, as do the intercostal spaces. They are broad at their articulation with the ribs and taper as they pass anteriorly and toward the midline. 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 superomedially towards the sternum or cartilage above, in a plane slightly anterior to their ribs.
Each costal cartilage has two surfaces, borders and ends. The external (anterior/anterosuperior) surface is convex. The sternoclavicular articular disc, costoclavicular ligament and subclavius are all attached to the external surface of the first costal cartilage, pectoralis major is attached to the medial ends of the first six costal cartilages, rectus abdominis to the fifth to seventh and others, including the costal cartilages forming the costal arch (margin) offer attachment sites for the muscles of the anterior abdominal wall. The internal (posterior/posteroinferior) surface is concave. Sternothyroid is attached to the internal surface of the first costal cartilage, transversus thoracis is attached to the second to seventh costal cartilages, and transversus abdominis is attached to the seventh to twelfth costal cartilages. The internal intercostal muscles and external intercostal membranes are attached to the concave superior and convex inferior borders. At around the point (apex) of maximum convexity of the inferior border of the sixth (sometimes the fifth) to ninth costal cartilages an inferiorly facing oblong articular facet articulates with a superiorly facing articular facet on the superior border of the cartilage below via a synovial interchondral joint. The lateral end of each cartilage articulates with its corresponding rib. The medial end of the first cartilage articulates with the manubrium of the sternum; the medial ends of the six succeeding cartilages are round and articulate with shallow costal notches on the lateral margins of the body of the sternum (and the manubrium in the case of the second); those of the eighth to tenth are pointed and articulate with the costal cartilage above; and those of the eleventh and twelfth are pointed and free. With the exceptions of the fibrous synarthrosis between the first rib and sternum, and the costal cartilages of the ninth and tenth ribs, all the articulations are synovial. Costal cartilages may undergo calcification with age ( ).
Rib fractures
Despite their pliability, the ribs are much more frequently broken when compared to the sternum; the anterior and anterolateral portions of the middle to lower ribs are the most vulnerable. The elastic recoil of the ribs that articulate with and effectively suspend the sternum may explain the rarity of sternal fractures. Because traumatic stress is often the result of compression of the thorax, the usual site of fracture is just anterior to the angle of the rib, the weakest point of the bone, however direct impact may fracture a rib at any point. Nearly 10% of all patients admitted after blunt force thoracic trauma have one or more rib fractures. Morbidity and mortality increase as the number of fractured ribs increases ( ): the ends of the broken bone may be driven inwards and potentially injure thoracic or upper abdominal viscera ( ). The pain associated with rib fracture, particularly multiple rib fractures in older adults, can predispose to pneumonia by limiting normal airway protective mechanisms (e.g. cough).
Joints
Manubriosternal joint
The manubriosternal joint lies between the manubrium and the body of the sternum approximately 7 cm below (inferior to) the jugular (suprasternal) notch of the manubrium. It is usually a symphysis but may be synovial, synchondrotic or synostotic. The bony surfaces are covered by hyaline cartilage and connected by a fibrocartilage that may ossify with increasing age. The central part of the disc is sometimes absorbed so that the joint appears synovial. Occasionally, in individuals over the age of 30 years, the manubrium appears to be joined to the body of the sternum by bone. However, the intervening cartilage may be only superficially ossified because ossification is not completed until late adult life. 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
There is a small range of angulation between the longitudinal axes of the manubrium and the body of the sternum, and limited anteroposterior displacement. The powerful ligamentous attachments in this region mean that dislocation of the manubriosternal joint is rare, although it may be associated with high-energy trauma. Dislocation is most common when the joint is synovial, whereas synchondral and synosteal types typically fracture through the manubrium.
Xiphisternal joint
The joint between the xiphoid process and body of the sternum is a symphysis. It is usually transformed to a synostosis by the fortieth year but sometimes remains unchanged, even in older adults.
Sternoclavicular joint
The sternoclavicular joint is described in Chapter 49 .
Costovertebral, sternocostal and interchondral joints
The heads of the ribs articulate with the bodies of the vertebrae at costovertebral joints; their necks and tubercles articulate with transverse processes at costotransverse joints.
Joints of the heads of the ribs
The head of a typical rib articulates with facets (often termed demifacets) on the margins of the bodies of adjacent thoracic vertebrae and with the intervening intervertebral disc ( Figs 53.11 – 53.12 ). The first and tenth to twelfth ribs articulate with their corresponding vertebra alone by a simple synovial joint. For the second to ninth ribs, 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 a plane joint, the articular surfaces are slightly ovoid and the superior and inferior synovial articulations are obtusely angled to each other. The ligaments associated with the joints are capsular, radiate and intra-articular.
Fibrous capsule
A fibrous capsule connects the head of the rib to the circumference of the articular surface formed by an intervertebral disc and the demifacets of two adjacent vertebrae. Some of the superior fibres of the capsule traverse the intervertebral foramen to blend with the posterior aspect of the associated intervertebral disc. The posterior fibres are continuous with the costotransverse ligament.
Radiate ligaments
The radiate ligaments connect the anterior surface of the head of each rib, just distal to its articular surface, to the bodies of two articulating vertebrae and their intervening intervertebral disc. Superior fibres ascend to the body of the vertebra above, inferior fibres descend to the body of the vertebra below, and intermediate fibres, which are the shortest and least distinct, pass horizontally to the intervening intervertebral disc. The radiate ligament associated with the first rib is attached to the bodies of the seventh cervical and first thoracic vertebrae. The tenth to twelfth ribs articulate with single vertebral bodies and the radiate ligament is attached to the body of the corresponding vertebra and the body of the vertebra above.
Intra-articular ligament
The intra-articular ligament is a short flat band that joins the crest on the head of the rib, between the articular facets, to the intervertebral disc and so divides the synovial joint into two compartments. The ligament is absent from the first and tenth to twelfth costovertebral joints.
Costotransverse joints
The facet on the tubercle of a rib articulates with the costal facet on the transverse process of its corresponding vertebra (see Figs 53.11 , 53.12 ). The eleventh and twelfth ribs lack this articulation. In the upper five or six joints, the articular surfaces are reciprocally curved; they are flatter in the joints located inferiorly ( Fig. 53.13 ). The ligaments associated with the costotransverse joints are capsular, costotransverse, superior and lateral costotransverse, and accessory.
Fibrous capsule
The fibrous capsule is thin, attached to articular peripheries and has a synovial lining.
Costotransverse ligament
The costotransverse ligament fills the costotransverse foramen between the neck of a rib and the transverse process of its adjacent corresponding vertebra. Its numerous short fibres pass posteriorly from a rough area on the posterior surface of the neck of the rib to the anterior surface of the transverse process. A costotransverse ligament is rudimentary or absent in the eleventh and twelfth ribs.
Superior costotransverse ligament
The superior costotransverse ligament has anterior and posterior layers. The anterior layer is attached between the crest on the neck of the rib and the inferior surface of the transverse process of the vertebra above, and blends laterally with the internal intercostal membrane; it is crossed by the intercostal vessels and nerve. The posterior layer is attached posteriorly on the neck of the rib, ascends posteromedially to the transverse process of the vertebra above, and blends laterally with the external intercostal muscle. The first rib has no superior costotransverse ligament. The inferior surface of the head, neck and sometimes the medial part of the shaft of the twelfth rib are connected to the transverse processes of the first and second lumbar vertebrae by the lumbocostal ligament.
Accessory ligament
An accessory ligament is usually present. It lies medial to the superior costotransverse ligament, from which it is separated by the dorsal ramus of a thoracic spinal nerve and accompanying vessels. Its attachments are variable, but it usually passes from a depression medial to the tubercle of the rib to the inferior articular process and the base of the transverse process of the vertebra above.
Lateral costotransverse ligament
The lateral costotransverse ligament is short, thick and strong. It passes obliquely from the apex of the transverse process of a vertebra to the rough non-articular part of the tubercle of the corresponding rib (see Figs 53.9 , 53.12 ). The ligaments of the upper ribs appear to ascend from the transverse processes of the vertebrae, and are shorter and more oblique than those of the lower ribs, which appear to descend.
Movements
The strong, tight radiate and intra-articular ligaments attached to the head of a rib only permit slight gliding at the costovertebral joints. Strong ligaments bind the necks and tubercles of the ribs to the transverse processes of the vertebrae and limit movements at the costotransverse joints to slight gliding, guided by the shape and direction of the articular surfaces (see Fig. 53.13 ). The facets on the tubercles of the first six ribs are oval and vertically convex, and fit corresponding concavities on the anterior surfaces of the transverse processes of the vertebrae; up and down movements of tubercles consequently involve rotation of the costal necks about their long axes. The facets on the tubercles of the seventh to tenth ribs are almost flat and face posteriorly, inferiorly and medially; the opposing articular surfaces are located on the superior aspects of the transverse processes, which means that when these tubercles move superiorly, they also move posteromedially. Both the costovertebral and costotransverse joints move simultaneously and in the same directions; the neck of a rib therefore moves as if at a single joint in which the costovertebral and costotransverse joints form its ends.
The main movement of the neck of each of the first six ribs is one of rotation about its long axis (a slight superior–inferior movement is also seen): a downward rotation of its anterior surface is therefore associated with depression, and an upward rotation with elevation, of the shaft and anterior end of the rib. The shape of the costotransverse joint in the seventh to tenth ribs means that the neck of the rib ascends posteromedially or descends anterolaterally, increasing or decreasing the infrasternal angle, respectively; slight rotation accompanies these movements.
Sternocostal joints
The costal cartilages articulate with small concavities (costal notches) on the lateral sternal borders at the sternocostal joints ( Fig. 53.14 ). The first sternocostal joint is an unusual type of synarthrosis (fibrous joint) and is often inaccurately called a synchondrosis. The second to seventh sternocostal joints are synovial, although articular cavities are often absent, particularly in the lower joints. Fibrocartilage covers the articular surfaces and also unites the costal cartilages and the sternum in those joints where cavities are absent. The seventh sternocostal joint may be synovial or symphysial. Ligaments associated with the joints include capsular, radiate sternocostal, intra-articular and costoxiphoid.
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