The chest wall is comprised of skin, fat, muscles, and the thoracic skeleton. It provides protection to vital organs (eg, heart and major vessels, lungs, liver) 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.
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. Thoracostomy needle decompression of a pneumothorax is performed along this line at the second or third intercostal space.
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.  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 mammaplasty. 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.
The thoracic skeleton is bounded by the 12 thoracic vertebrae (T1 through T12) posteriorly, from which 12 sets of bony ribs articulate and wrap around laterally then anteriorly, forming the posterior and lateral borders of the thoracic skeleton, before finally connecting with the sternum and costal cartilages in the medial anterior chest.
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 11th and 12th thoracic vertebrae have a single superior costal facet and no transverse process articular facet.
The twelve 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.
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.
Twelve ribs are noted, with the first 7 referred to as true ribs because they connect to the sternum and manubrium directly. Ribs 8 through 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 a head with two articular facets, a neck, a tubercle with one articular facet, and a shaft that terminates at the costochondral joint.
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 and greater between the upper ribs than the lower ribs, which is important to note, for example, when placing a large bore thoracostomy tube.
The medial anterior chest is defined by the sternum, which consists of 3 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.
Embryologically, the manubrium forms first, followed by the sternal body and then the xiphoid process. The manubrium is located at the level of the T3 and T4 vertebral bodies and is the widest and thickest of the 3 sternal bones. A palpable landmark on the manubrium is the jugular or suprasternal 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 body of the sternum is located at the level of vertebral bodies T5 through T9. The xiphoid process is the smallest and thinnest bone of the sternum. Although it often comes to a point, other normal variants include blunt, bifid, or curved. The xiphoid is cartilaginous in younger people but is nearly completely ossified by age 40 years. 
The thoracic skeleton provides attachments for muscles within the thorax as well as for muscles to the neck, abdomen, upper limbs, and back.
Each intercostal space is spanned by a trilayer of muscle. The outermost external intercostal muscles are obliquely oriented, running in an anteroinferior direction and function to elevate the rib. The internal intercostals are obliquely oriented in a posteroinferior direction and functions to depress the ribs. 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. The intercostal blood supply is derived from the posterior intercostal branches of the aorta and the anterior intercostal branches of the internal thoracic artery.
This can be considered part of the group of innermost intercostal muscles located in a layer deep to the intercostal neurovascular bundles. It consists of 4 or 5 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 pectoralis major muscle originates from the medial clavicle and lateral sternum and inserts 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 mammary artery providing a segmental blood supply. [3, 4, 5] The medial and lateral pectoral nerves provide innervation for the muscle, entering posteriorly and laterally.
The action of the pectoralis major is to flex, adduct, and rotate the arm medially. The pectoralis minor 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.
The serratus anterior, as its name suggests, 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. It is has a Mathes and Nahai classification type II blood supply, with its major contribution from the lateral thoracic artery and minor contribution from 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. [6, 7]
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.
The subclavius muscle is a small muscle that arise from 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.
The latissimus dorsi is the largest muscle in the body, with broad origin from the posterior ilium, back of the sacrum, spinous processes of T6 or T7 through L5, the thoracolumbar fascia, posterior ribs 8 or 9 through 12, and the 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 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 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.
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. The 7th-12th intercostal nerves 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 8 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. The 7th-12th intercostal nerves serve to innervate the external oblique, and it 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 8 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 3 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 injuring during abdominal wall surgery.
Directly off of either subclavian vessel are the inferiorly coursing internal thoracic artery and vein (also known as the internal mammary artery). [8, 9, 10] 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 the primary donor vessels for free tissue transfer. The internal mammary (internal thoracic) arteries are also commonly used in cardiac bypass, and sacrifice of the artery must be noted in patients needing sternal reconstruction for post–cardiac bypass wound infections.
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. The internal thoracic arteries, also known as the internal mammary arteries, supply the anterior intercostal branches to the first 6 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 are located in the second and third intercostal space and are routinely accessed as sites for vascular anastomosis during free tissue transfer in breast reconstruction.
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 4 distinct branches: the pectoral, acromial, deltoid, and clavicular. The pectoral branch is the dominant blood supply to pectoralis minor and major. 
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 2nd 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. 
The medial and lateral pectoral nerves, also known as the medial and lateral anterior thoracic nerves are branches of the medial and lateral cords of the brachial plexus, respectively. The medial pectoral nerve is supplied from spinal roots C6 through T1 and originates medial and posterior to the axillary artery 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 then crosses anterior to the artery more proximal than the medial pectoral 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.  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 when dissecting near the posterior border of the pectoralis minor and 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.  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
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 around 40 mm,  but sizes vary with age and breast feeding history. Mean diameter of the nipple is 1.3 cm, and mean height is 0.9 cm.  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). [16, 17]
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. Breast sexual maturity is usually complete around age 18-20 years. 
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 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. In prophylactic mastectomy patients, the Coopers 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 the normal breast the nipple should be above the IMF.
Grades of breast ptosis described by Regnaul are as follows: 
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
Most of the breast parenchyma is positioned at or below the IMF giving the appearance of pendulous breasts, but the nipple is in 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). 
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.  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.  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.  Extrathoracic extension of thoracic visceral tumors such a 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 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 3 rib segments, reconstruction of the rigid wall is needed in addition to soft tissue coverage to prevent paradoxical motion of the chest wall in the areas without rib support. Surgical stabilization in these cases has been shown to decrease mechanical ventilator days, improve long-term outcome, and lower cost of hospitalization in select patients. [21, 22]
Sternal wound infection after coronary artery bypass graft (CABG) has been another major area requiring reconstruction. [23, 24, 25] Risk factors for sternal dehiscence and subsequent infection are obesity, diabetes, chronic obstructive pulmonary disease (COPD), and bilateral harvest of internal thoracic arteries. The standard treatment for sternal infections is 3-fold: 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.