Chest Wall Anatomy

The chest wall comprises the skin, fat, muscles, and thoracic skeleton. It provides protection to vital organs (e.g., heart and major vessels, lungs, liver), supports respiratory mechanics, ^[1] and provides stability for movement of the shoulder girdles and upper arms. Although the thoracic skeleton consists of rigid bones and cartilage, its interconnection with the muscular components forms for a dynamic structure that is able to expand during inspiration, thereby increasing intrathoracic volume and allowing for maximal breaths to take place. An in-depth understanding of chest wall anatomy is paramount to those performing any surgical procedure of the chest or breast.

Identifying and marking the relevant surface anatomy of the chest wall can assist in preparation for surgery on the chest.

Surface anatomy

Anterior landmarks of the chest include the nipple and sternal notch. The mid-sternal line (anterior median) is marked along the sternum from the sternal notch to the xiphoid process and, if needed, can be extended down the linea alba to the umbilicus. This anatomical midline can be useful in assessing for symmetry in breast augmentation or in performing a median sternotomy. The lateral sternal line is marked along the lateral border of the sternum and can help identify the internal thoracic artery as it runs along the inside of the chest wall approximately 1 cm lateral to this line. The mid-clavicular line is drawn through the middle of the clavicle and, in males, typically runs just medial to the nipple and areola (see illustration below). Thoracostomy needle decompression of a pneumothorax is performed along this line at the second or third intercostal space. Xiphoid process is the inferior end of the sternum that is located at T9-T10 vertebral levels. It serves as a landmark for cardiopulmonary resuscitation (CPR) and subxiphoid surgical approaches. ^[2]

Lateral landmarks include the axillary fossa (armpit). The axilla is bounded superiorly by the outer border of the first rib, the middle third of the clavicle, and the superior border of the scapula. Inferiorly, its extent is defined by the lower border of the axillary fossa. The anterior border includes the pectoralis muscles, and the posterior border includes the latissimus dorsi, which are both visible at the skin surface as the anterior and posterior axillary folds, respectively. ^[3] The anterior axillary line is drawn along the anterior axillary fold and followed down the chest wall. This line can be used as a landmark for placement of a thoracostomy tube or in defining the lateral contour of the breast in reduction mammoplasty. The posterior axillary line is drawn along the posterior axillary fold and followed down the chest wall. The mid-axillary line runs down through the apex of the axillary fossa.

Skeleton

The osseocartilaginous frame of the chest typically consists of 12 pairs of ribs, which articulate with the 12 thoracic vertebrae posteriorly. Anteriorly they articulate with the sternum, except for the last two or three pairs of ribs, via their costal cartilages. ^[1] Together, these form a protective cage around vital organs such as the heart and lungs while also facilitating respiratory movements. ^[1]

Thoracic vertebrae

On the posterolateral aspect of each thoracic vertebral body are a pair of superior and inferior costal articular facets. The costal facet of the transverse process is located on the anterolateral aspect of its tip. The first thoracic vertebra (T1) has a complete superior costal facet for the first rib and an inferior demifacet for the second rib. T10 typically has a superior demifacet. ^[4] The 11th and 12th thoracic vertebrae have a single pair of costal facets that articulate with the 11th and 12th ribs, respectively. ^[4]

Transverse processes possess costal facets (except T11 and T12) for articulation with the tubercles of ribs at the costotransverse joints. ^[5] Spinous processes are long and angled downward, overlapping with the vertebra below, contributing to the stability of the spine. ^[1]

The 12 thoracic vertebrae (T1-T12) are interdigitated by each rib with two articulations between the vertebral bodies.

The costovertebral joint includes a connection between the head of the rib and the inferior costal facet of the vertebral body that the rib is numbered after and a connection between the inferior costal facet of the vertebral body above. The two facets of the joint are partially divided by an interarticular ligament between the crest of the head of the rib and the intervening intervertebral disk.

The costotransverse joint is a synovial joint between the tubercle of the rib and the transverse process of the vertebral body that the rib is numbered after. These joints contain oval-shaped facets with a major axis, vertical at the upper vertebrae and almost horizontal at the lower vertebrae. Because of this type of structure, the cranial ribs move on the sagittal plane while the caudal ribs move on the transverse plane. ^[6]

The thoracic intervertebral foramen is bounded superiorly and inferiorly by the pedicles of the two adjacent vertebrae, anteriorly by the vertebral bodies and posteriorly by the base of each transverse process. The thoracic spinal ganglion and nerve roots emerge from these foramina.

Ribs

The 12 pairs of ribs are categorized into three groups based on their attachment to the sternum. ^[1] The first seven are referred to as true ribs because they connect to the sternum and manubrium directly via costal cartilages. ^[1] Ribs 8-10 are referred to as false ribs because their costal cartilages conjoin to form a single indirect connection to the sternum via the costal arch. Ribs 11 and 12 are referred to as floating ribs because their anterior extremity lies freely in the posterolateral abdominal wall with no attachment to the sternum.

Each rib has:

• Head with two articular facets for articulation with the bodies of adjacent thoracic vertebrae ^[1]
• Neck, a narrow segment ^[1]
• Tubercle with one articular facet for articulation with the transverse process of the corresponding vertebra ^[1]
• Shaft, an elongated portion that curves laterally and anteriorly that terminates at the costochondral joint where it meets the costal (hyaline) cartilage ^[1]

Posteriorly, the heads of the ribs interdigitate with the vertebrae and are numbered according to the inferior vertebra. Joints between the ribs and thoracic vertebrae were reviewed in the above subsection on thoracic vertebrae. The bony ribs arc laterally and anteriorly, then medially where the next major junction is the costochondral joint. These are hyaline cartilage joints where the rib and cartilage are firmly attached through a continuity of the overlying periosteum and perichondrium.

The ribs/costal cartilages have various attachments to the sternum. The first pair of ribs articulates with the sternum through cartilaginous joints or synchondroses and is relatively immobile. The second through seventh pairs of costal cartilages articulate with the sternum at synovial joints that move during respiration and are reinforced by sternocostal ligaments.

The neurovascular bundles arising from the spine and aorta travel anteriorly along the inferior aspect of each rib within the costal groove. Injury to these structures should be avoided when entering rib spaces by dissecting over the superior border of the inferior rib. The intercostal space heights are greater anteriorly than posteriorly (greater between the upper ribs than the lower ribs), which is important to note for example when placing a large bore thoracostomy tube.

Sternum

The sternum, a central component of the thoracic skeleton, is a flat, elongated bone situated in the anterior midline of the chest wall. ^[7]  It consists of three flat polygonal bones: the manubrium, sternal body, and xiphoid process. These bones develop independently of the ribs and are first apparent at approximately 35 days' gestation as a pair of mesenchymal bars lateral to the ventral midline in the thoracic region. These components are connected by secondary cartilaginous joints (symphyses), which contribute to the structural integrity and flexibility of the thoracic cage. ^[1]

The sternum originates from paired mesenchymal bars located lateral to the ventral midline in the thoracic region. These bars begin to chondrify and fuse in a craniocaudal direction during fetal development. ^[8]  Embryologically, the manubrium forms first, followed by the sternal body and then the xiphoid process. Ossification occurs in a superior-to-inferior sequence, with centers appearing from the fifth month of gestation through early childhood. Fusion of the sternal body segments typically proceeds caudocranially and is completed by early adulthood. ^{[8, 9]}

The manubrium is the most superior portion of the sternum, which is roughly quadrangular in shape. ^[10] It is located at the level of the T3 and T4 vertebral bodies and is the widest and thickest of the three sternal bones. A palpable landmark on the manubrium is the jugular or sternal notch, which is bounded on either side by the medial attachments of the clavicles. The manubrium and sternal body lie in slightly different planes and their junction at the manubriosternal joint is usually projected. The manubrium articulates with the clavicles and the first pair of ribs. Its inferior border forms a secondary cartilaginous joint with the sternal body at the manubriosternal joint, also known as the sternal angle or the Angle of Louis, which lies approximately at the T4-T5 vertebral level. ^[1]

The body of the sternum is the longest segment ^[1] located at the level of vertebral bodies T5-T9. It develops from four sternebrae that fuse during childhood to early adulthood. ^[9] The lateral borders exhibit articular facets for attachment to costal cartilages of ribs 2-7. ^[1] Faint transverse ridges or cartilaginous intersections on its anterior surface mark sites of fusion between sternebrae. ^[11]

The xiphoid process is the smallest and thinnest bone of the sternum. It is located inferiorly at approximately T10 vertebral level. ^[12] Although it is often pointed in shape, other normal variants include blunt, bifid, or curved. The xiphoid is cartilaginous in younger people but is nearly completely ossified by the age of 40 years. ^[13]

The sternum provides critical attachment sites for several muscles, including pectoralis major (anteriorly), sternocleidomastoid (superiorly), sternohyoid, and sternothyroid (posteriorly). It also anchors the superior sternopericardial ligament connecting to the pericardium. ^[1] The sternal angle serves as a key anatomical landmark for clinical examination and medical procedures, including locating the second pair of costal cartilages, auscultation, and imaging studies. ^[1]

Muscles

Intercostal muscles

The intercostal muscles are a group of intrinsic muscles located in the thoracic wall, spanning intercostal spaces between adjacent ribs. ^[14]  There are 11 pairs of external and internal intercostal muscles, and the innermost intercostal has a variable presence. ^[1]

The outermost external intercostal muscles are obliquely oriented, running in an anteroinferior direction and function to elevate the rib. They extend from the tubercles of the ribs posteriorly to the costal cartilage, where each continues forward to the sternum as the external intercostal membrane. ^[15]

The internal intercostals are obliquely oriented in a posteroinferior direction and function to depress the ribs. They originate from the floor of a costal groove and adjacent costal cartilage and insert into the superior border of the rib below. Their muscle fibers are directed obliquely, almost at right angles to those of the external intercostal muscles. ^{[16, 1]}

The innermost intercostals are a thin variable layer of muscle, with fibers oriented similarly to those of the internal intercostals and are separated from them by the intercostal neurovascular bundles. These muscles are insignificant and sometimes absent in the upper intercostal spaces. They become progressively more substantial in the lower spaces. ^[1]

The intercostal blood supply is derived from the posterior intercostal branches of the aorta and the anterior intercostal branches of the internal thoracic artery (see illustration below).

Transversus thoracis

The transversus thoracis is a thin, flat muscle located on the inner surface of the anterior thoracic wall. ^[17] It can be considered part of the group of innermost intercostal muscles located in a layer deep to the intercostal neurovascular bundles. It consists of four or five slips of muscle that attach to the posterior surface of the xiphoid process and inferior sternal body. The slips pass superolaterally to attach to the second through sixth costal cartilages. The primary action of this muscle is to depress the ribs during expiration, functioning as an accessory muscle of respiration. The transversus thoracis is relevant in surgical procedures, particularly during internal thoracic artery harvesting for coronary artery bypass grafting. Its variations can influence surgical approaches as it may partially or completely cover the internal thoracic artery along its course. ^[17]

Pectoralis major/minor

The pectoralis major is a large, fan-shaped muscle of the anterior chest wall. It originates from the anterior surface of the medial half of the clavicle, the anterior surface of the sternum, the first seven costal cartilages, the sternal end of the sixth rib, and the aponeurosis of the external oblique of the anterior abdominal wall. ^[18] These fibers insert on the lateral lip of the bicipital groove of the humerus.

It has a Mathes and Nahai classification type V blood supply, with the thoracoacromial artery as the major blood supply and the intercostal perforators arising from the internal thoracic (mammary) artery providing a segmental blood supply. ^{[19, 20, 21]}

The medial and lateral pectoral nerves provide innervation for the muscle, entering posteriorly and laterally, with some fibers from both nerves forming an anastomotic loop known as "ansa pectoralis." ^[22] The action of the pectoralis major is to flex, adduct, and rotate the arm medially.

The pectoralis minor, a smaller triangular muscle located deep to the pectoralis major, ^[23] originates from the third to fifth ribs near the costal cartilages and inserts on the medial border and superior surface of the coracoid process of the scapula. It is innervated by the medial pectoral nerve and functions to stabilize the scapula by drawing it inferiorly and anterior against the thoracic wall.

Serratus anterior

The serratus anterior is a fan-shaped muscle located on the anterolateral thoracic wall. ^[24] As its name suggests, it consists of multiple muscle slips that run along the anterolateral chest wall (see Figure 1 for surface anatomy). It originates from the upper borders of the first through eighth ribs and inserts on the deep surface of the medial scapula. The muscle passes deep to the scapula, wrapping posteromedially around the ribcage. ^[24]

The muscle is divided into three parts based on its insertion points: ^[24]

• Superior part - Inserts near the superior angle of the scapula
• Intermediate part - Inserts along the medial border
• Inferior part - Inserts near the inferior angle and is the most prominent and powerful section

It has a Mathes and Nahai classification type II blood supply, with its major contribution from the lateral thoracic artery and minor contribution from the serratus branches of the thoracodorsal artery. The lateral thoracic artery generally supplies the upper 3-5 slips, while the thoracodorsal artery generally supplies the lower slips. Innervation is from the long thoracic nerve, where activation of the serratus causes rotation of the scapula, raising the tip of the scapula upward and drawing the body of the scapula toward the chest wall, thereby protracting it. Transection of the long thoracic nerve results in scapular winging, where the scapula moves upward and posteriorly away from the chest wall. ^{[25, 26]}

Other muscles with attachments to the thoracic skeleton

The subclavius, latissimus dorsi, serratus posterior superior and inferior, and the abdominal wall muscles find their attachments to the thoracic skeleton and may be encountered in surgery of the chest or breast.

Subclavius

The subclavius muscle is a small muscle arising from the first rib and its costal cartilage and inserts onto the deep surface of the clavicle, functioning to depress the clavicle. It is innervated by the subclavian nerve. Clavicle or first rib fractures can involve injury to this muscle that overlies and protects the subclavian vessels and a portion of the brachial plexus.

Latissimus dorsi

The latissimus dorsi is the largest muscle in the body, with a broad origin from the posterior ilium, back of the sacrum, spinous processes of T6 or T7 through L5, thoracolumbar fascia, posterior ribs 8 or 9 through 12, and inferior angle of the scapula. It inserts onto the intertubercular groove of the humerus and functions to adduct, extend, and internally rotate the arm. It has a Mathes and Nahai type V blood supply, with major contribution from the thoracodorsal artery and segmental contribution from the perforating branches of the intercostal and lumbar arteries. Innervation is from the thoracodorsal nerve. It is a muscle frequently encountered during mastectomy and axillary dissection and can be used as a rotational flap in breast or chest wall reconstruction with or without a skin paddle.

Serratus posterior superior and inferior

The serratus posterior muscles are thin, accessory muscles of respiration located deep to the rhomboids (superior) and latissimus dorsi (inferior). ^[27]

The serratus posterior superior originates on the nuchal ligament and spinous processes of C7 through T3 and inserts on the superior posterior aspect of ribs 2 through 5. It functions to elevate the superior ribs aiding in forced inspiration.

The serratus posterior inferior originates on the spinous processes of T11 through L2 and inserts on the inferior posterior aspect of ribs 9 through 12. It functions to draw the ribs backward and downward to assist in rotation and extension of the trunk and contributes to forced expiration of air from the lungs.

Both muscles obtain their blood supply from intercostal arteries and are innervated by intercostal nerves.

Abdominal muscles

The abdominal wall muscles contribute significantly to thoracic stability and movement by attaching to the lower ribs. ^[28] The rectus abdominis muscle originates at the crest of the pubis and inserts on the xiphoid process and cartilages of the fifth through seventh ribs. It has a Mathes and Nahai classification type III blood supply with codominant sources from the inferior and superior epigastric arteries. Intercostal nerves 7-12 provide sensation to overlying skin and innervate the muscle, which functions to compress the abdomen and flex the spine. These nerves course in the space located between the internal oblique and transversus abdominis, giving off perforating branches.

The external oblique muscle is a broad muscle that runs along the anterolateral abdomen and chest wall. Its origin is from the lower eight ribs, and its insertion is along the anterior half of the iliac crest and the aponeurosis of the linea alba from the xiphoid to the pubis. Intercostal nerves 7-12 serve to innervate the external oblique, which functions to compress the abdomen, flex and laterally rotate the spine, and depress the ribs. It has a Mathes and Nahai classification type IV blood supply with segmental sources from the inferior eight posterior intercostal arteries. The external oblique muscle abuts the inferolateral aspect of the chest and breast. It is elevated along with the rectus abdominis fascia to provide inferior coverage of the breast implant during reconstructive surgery.

The internal oblique is the middle of the three abdominal muscles that attaches to the lower part of the thoracic cage. Its origin is along the iliac crest and lateral half of the inguinal ligament, and it inserts on the inferior borders of the 10th-12th ribs. The fibers run in an inferior lateral direction, the opposite of the external oblique.

The transversus abdominis muscle is an abdominal wall muscle that is continuous superiorly with the transversus thoracis, the innermost of the chest wall muscles. It originates from the internal surfaces of the 7th-12th ribs, thoracolumbar fascia, and iliac crest. It inserts along the linea alba with the aponeurosis of the internal oblique. The fibers run in a transverse medial direction. Just deep to the internal oblique and superficial to the underlying transversus abdominis is a neurovascular plane. This neurovascular plane contains branches of the intercostals, subcostal, iliohypogastric, and ilioinguinal nerves that are important to avoid injury during abdominal wall surgery.

Neurovascular Structures

Vascular anatomy

Directly off of either subclavian vessel is the inferiorly coursing internal thoracic artery and vein (also known as the internal mammary artery). ^{[29, 30, 31]} Each artery courses inferiorly along its respective side of the sternum giving off intercostal branches. The patency of these arteries is important in breast reconstruction because they serve as primary donor vessels for free tissue transfer. The internal mammary arteries are also commonly used in cardiac bypass, and sacrifice of the artery must be noted in patients requiring sternal reconstruction for postcardiac bypass wound infections.

The internal thoracic arteries supply the anterior intercostal branches to the first six intercostal spaces and then bifurcate at the level of the sixth intercostal space into the musculophrenic arteries that track laterally along the costal margin and the superior epigastric arteries that pass into the rectus sheath beneath the rectus abdominis muscle. Perforators from the anterior intercostal vessels extending from the medial aspect of the chest wall also supply the overlying muscle, fascia, and skin. The largest of the internal mammary artery intercostal perforators is located in the second and third intercostal space and is routinely accessed as a site for vascular anastomosis during free tissue transfer in breast reconstruction.

Each posterior intercostal artery branches laterally along the inferior aspect of each rib in a neurovascular bundle. The bundle is oriented with the vein, artery, and nerve from superior to inferior.

Laterally and superiorly on the chest wall, blood supply is derived from the superior thoracic artery, thoracoacromial trunk, lateral thoracic artery, and thoracodorsal artery.

The thoracoacromial trunk is a direct branch of the second part of axillary artery and it has four distinct branches: the pectoral, acromial, deltoid, and clavicular. The pectoral branch is the dominant blood supply to pectoralis minor and major. ^[32]  

The lateral thoracic artery provides blood supply to the pectoralis major via a pectoral branch, with branches across the axilla supplying the axillary lymph nodes, and the subscapularis muscle. It originates from the second portion of the axillary artery and descends along the lateral edge of the pectoralis major and anterior lateral chest.

Located more lateral and superior in the axilla is the subscapular artery, which branches from the third part of the axillary artery. The subscapular artery bifurcates into the circumflex scapular, which arcs laterally and posteriorly, and the thoracodorsal artery, which courses inferiorly. The thoracodorsal, the major blood supply to the latissimus dorsi muscle, courses inferiorly and gives off additional branches to the serratus anterior muscle. ^[33]

Innervation

The medial and lateral pectoral nerves are branches of the medial and lateral cords of the brachial plexus, respectively.

The medial pectoral nerve is supplied from spinal roots C8 and T1 and originates medial and posterior to the axillary artery and then curves anterior to the axillary artery as it courses medially and inferiorly along the chest wall.

The lateral pectoral is supplied from spinal roots C5 through C7 and originates lateral to the axillary artery, crosses anterior to the artery more proximal than the medial pectoral, and then travels medially along the chest wall. The lateral pectoral nerve sends a branch to the medial pectoral forming a loop called the ansa pectoralis, which wraps around the axillary artery.

The medial pectoral nerve innervates the pectoralis minor and the sternocostal head of the pectoralis major, while the lateral pectoral nerve innervates only the clavicular head of the pectoralis major.

Both nerves enter the deep surface of their respective muscle targets. Pectoral nerve blocks have been described to aid with pain control after breast surgery. ^[34] See the figure below for a review of nerves arising from the brachial plexus.

The long thoracic nerve is supplied from spinal nerve roots C5 through C7 and innervates the serratus anterior.

The thoracodorsal nerve is a branch of the posterior cord of the brachial plexus supplied from spinal nerve roots C6 through C8. It follows the course of the subscapular artery along the posterior aspect of the axilla and innervates the latissimus dorsi on its deep surface.

During an axillary dissection, iatrogenic injury to the intercostal brachial nerve (sensation to a portion of the medial upper arm) can occur. Iatrogenic injury to the medial pectoral nerve may also occur while performing dissection near the posterior border of the pectoralis minor; this should be avoided as injury can result in atrophy of the pectoralis minor and the inferior portion of the pectoralis major muscles, causing relative show of the ribs. ^[35] Other neurovascular structures that are less commonly injured during axillary dissection include the lateral thoracic artery (blood supply to the serratus anterior), the long thoracic nerve (innervation of the serratus anterior), or the thoracodorsal artery and nerve (blood supply and innervation of the latissimus dorsi).

Sensation to the skin of the chest wall is derived from perforating branches of the intercostal nerves at various levels carrying afferent sensory information to the dorsal root ganglia of the thoracic spine. The intercostal nerves arise from the thoracic spinal trunks exiting the intervertebral foramen. From here, the intercostal nerves travel laterally and bifurcate once posteriorly to give rise to lateral cutaneous branches and then bifurcate anteriorly to give rise to anterior cutaneous branches. Sensation to the nipple areola complex is from the third and fourth intercostal nerves.

Skin and Breast

Surface anatomy

The chest is covered with skin with a moderate dermal layer. The skin is supplied by arterial perforators both laterally and medially and has a robust dermal vascular network. In a youthful breast, the nipple lies just above the inframammary crease and is usually level with the fourth intercostal space and just lateral to the midclavicular line with its surrounding areola.

The size and shape of areolae widely varies, with those of sexually mature women usually being larger than those of men and prepubescent girls. Human areolae shapes range from circular to elliptical. The average diameter of a male areola is approximately 23-28 mm. Sexually mature women have an average areola of around 40 mm, ^[36] but sizes vary with age and breast-feeding history. The mean diameter of the nipple is 1.3 cm, and the mean height is 0.9 cm. ^[36] Located radially on the female nipple are small openings known as lactiferous ducts, from which milk is released during lactation. Other small openings in the areola are sebaceous glands (Montgomery glands). ^{[37, 38]}

Breasts

The breasts consist of fatty tissue and glandular or milk-producing tissue interspersed with fibrous suspensory ligaments. The ratio of fatty tissue to glandular tissue varies among individuals with age and hormonal exposure. Sexual maturity of the breast is usually complete around the age of 18-20 years. ^[39]

The glandular tissue is organized into lobules connected by ducts that converge at the nipple-areolar complex, while the fatty tissue provides volume and contour. Cooper's ligaments extend from the dermis of the skin to the deep fascia overlying the pectoralis major muscle, providing structural support and maintaining breast shape. These ligaments also contribute to the dimpling appearance (peau d'orange) seen in certain pathological conditions such as inflammatory carcinoma. ^[40]

The base of the breast overlies the pectoralis major muscle between the second and sixth ribs and is anchored to the pectoralis major fascia by suspensory ligaments of the breast, also known as Cooper's ligaments. These ligaments are anchored to the deep fascia, course throughout the breast parenchyma, and attach to the dermis of the breast skin.

In terms of surgical margins, the breast is bordered by the sternum medially, the clavicle superiorly, the latissimus laterally, and the rectus muscle inferiorly. The axillary tail of the breast extends obliquely up into the medial wall of the axilla, by wrapping around the inferior border of the pectoralis major muscle. In prophylactic mastectomy patients, Cooper's ligament attachments to the dermis are where breast parenchyma can be left behind and breast cancer may develop.

The breast tissue and its suspensory ligaments relax with age and weight, resulting in ptosis of the breast over time. Breast ptosis is based on the position of the nipple in relation to the inframammary fold (IMF) graded from I to III. In a normal breast, the nipple should be above the IMF.

Grades of breast ptosis described by Regnaul are as follows: ^[41]

• Grade I – Nipple is at the level of the IMF, above the lower contour of the breast
• Grade II – Nipple is below the IMF but above the lower contour of the breast
• Grade III – Nipple is below the IMF and is the lowest point of the breast and oriented inferiorly

Pseudoptosis

Most of the breast parenchyma is positioned at or below the IMF, giving the appearance of pendulous breasts, but the nipple is in a normal position above the IMF.

Blood supply to the breast is robust and diverse, arising from the internal thoracic artery via large anterior intercostal perforators, the lateral thoracic artery, pectoral branch of the thoracoacromial artery via perforators running through the pectoralis, as well as anterior and posterior branches from the intercostal arteries (mainly fifth and sixth intercostal spaces). ^[39]

The following should also be considered:

Chest Wall Defects

Chest wall deformities can occur due to trauma, infection, congenital defects, neoplasm, and iatrogenic injuries from surgery or radiation.

The most common cause of chest trauma in the United States is blunt trauma associated with motor vehicle collision. Approximately 7% of these collisions result in serious thoracic injury, and 20% of all trauma deaths involve a thoracic injury. ^[42] Other traumatic injuries that may also necessitate chest wall reconstruction include penetrating chest trauma, blast, or burn injuries.

Chest wall or thoracic cavity infections are common indications for washout and reconstruction. Pneumonia, empyema, bronchopleural fistula, and surgical site infections such as sternal osteomyelitis may occur following thoracic or cardiac surgery and require prompt and complete debridement with reconstruction.

The most common congenital chest wall defects requiring reconstruction are pectus excavatum (inward concavity of sternum/anterior ribs), pectus carinatum (outward protrusion of sternum/anterior ribs), and Poland syndrome. ^[42] These defects become more apparent through skeletal growth and can cause psychosocial distress, thereby requiring reconstruction. In extreme pectus cases, even with normal heart and lungs, the rigid defect in position of the anterior chest wall may inhibit normal respiration and require accessory muscle use or decrease exercise tolerance. Other congenital conditions that may require chest wall reconstruction include lymphatic and vascular malformations.

Neoplasms of the chest wall can significantly affect form and function or can metastasize, which are indications for surgical resection. Breast carcinoma and soft tissue sarcoma are among the most common neoplasms that require chest wall resection. ^[42] Extrathoracic extension of thoracic visceral tumors such as lung cancer or primary bone and cartilage tumors are also indications for surgical resection that may cause large chest wall defects. When considering options for chest wall reconstruction after tumor resection, the potential need for chemotherapy and radiation must be considered due to the deleterious effects of these treatments and increased potential for wound complications.

Radiation treatment of chest wall tumors can result in wound complications that require further resection and alternate reconstructive options. Breast reconstruction is the most common need for chest wall radiation, and complications after radiation include wound dehiscence, infection, implant extrusion, or severe capsular contracture. Osteoradionecrosis of the ribs and the sternum can be a late complication following radiation treatment of carcinomas and lymphomas in the chest wall, resulting in devitalized bone, chronic wounds, and infection that may require extensive debridement and reconstruction.

Indications for Chest Wall Reconstruction

Soft tissue reconstruction of the chest wall is appropriate for defects less than 5 cm in diameter with no more than 2-3 rib segments lost because these are without significant functional consequence to respiration. In defects involving large areas or more than three rib segments, reconstruction of the rigid wall is needed in addition to soft tissue coverage to prevent paradoxical motion of the chest wall in areas without rib support. Surgical stabilization in these cases has been shown to decrease mechanical ventilator days, improve long-term outcomes, and lower the cost of hospitalization in select patients. ^{[43, 44]}

Sternal wound infection after coronary artery bypass graft has been another major area requiring reconstruction. ^{[45, 46, 47]} Risk factors for sternal dehiscence and subsequent infection are obesity, diabetes, chronic obstructive pulmonary disease, and bilateral harvest of internal thoracic arteries. The standard treatment for sternal infections is threefold: radical debridement of all infected tissues, culture-directed antibiotic therapy, and obliteration of dead space.

Chest wall reconstruction with vascularized tissue has proved to be an effective treatment and has lowered mortality rates in patients. Vascularized chest wall reconstruction is most commonly achieved using pectoralis myocutaneous advancement, rectus abdominis myocutaneous pedicled or free tissue transfer, or other flap procedures such as a pedicled latissimus dorsi or omentum flap.

Negative pressure wound therapy is being increasingly utilized as an adjunct or alternative to surgical intervention in select cases with minimal bony exposure or instability. ^[48]

Additionally, approaches such as extended anterolateral thigh flaps have been employed successfully for massive chest wall defects exceeding two thirds of the thoracic surface. ^[49]

Rigid reconstruction materials often include composite prostheses such as polypropylene mesh combined with methyl methacrylate or Gore-Tex mesh. ^[50] Advances in reconstruction techniques, including the use of synthetic meshes and biologic materials, have further improved functional and aesthetic outcomes while reducing morbidity. Careful patient selection and precise surgical techniques are critical to minimizing complications. ^[51]