Chest Wall

The chest wall consists of skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, fat, muscles, bones, and cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. The interconnections between the bones, cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage, and muscles allow for the rhythmic expansion and reduction of the chest wall during breathing, which facilitates changes in intrathoracic pressure to allow expansion of the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs during inspiration. The extrinsic muscles have 2 bony attachments; the intrinsic muscles only attach to the thoracic skeleton.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Introduction

Embryology

  • The thorax develops from the embryonic neural tube.
  • The neural tube consists of all 3 embryonic layers:
  • The chest wall develops from the mesoderm.

Components of the chest wall

  • 2 openings: superior and inferior thoracic apertures
  • The thoracic skeleton is formed by: 
    • 12 ribs 
    • 12 thoracic vertebrae 
    • Cartilage 
    • Sternum
  • Joints:
    • Intervertebral disc joint: occupies space between vertebrae and absorbs pressure on the spine
    • Costovertebral joint: connects the proximal end of the ribs with corresponding thoracic vertebrae
    • Costochondral joint: connects the ribs to costal cartilages
    • Sternocostal joint: connects the costal cartilages of the 1st 7 ribs to the sternum
    • Sternoclavicular joint: connects the clavicle to the sternum
    • Interchondral joint: connects costal cartilages of ribs 7–10
  • Muscles:
    • Intrinsic thoracic muscles: connect only to the thoracic skeleton:
      • External intercostal muscles
      • Internal intercostal muscles
      • Innermost intercostal muscles
      • Subcostal (posteriorly) muscles
      • Transversus thoracis muscles (anteriorly)
      • Levatores costarum muscles
      • Serratus posterior superior and inferior muscles
    • Extrinsic thoracic muscles: connect to other parts of the skeleton:
      • Pectoralis major and pectoralis minor muscles
      • Serratus anterior muscles
      • Subclavius muscles
  • Breasts Breasts The breasts are found on the anterior thoracic wall and consist of mammary glands surrounded by connective tissue. The mammary glands are modified apocrine sweat glands that produce milk, which serves as nutrition for infants. Breasts are rudimentary and usually nonfunctioning in men. Breasts: composed of:
    • Mammary glands
    • Fibrous tissue
    • Fat
    • Areolar complex 
    • Nipple

Thoracic Skeleton

Ribs

The thoracic skeleton consists of 12 pairs of ribs.

Classification:

  • Vertebrosternal (true ribs): 
    • Ribs 1–7
    • Connect directly to the sternum via the costal cartilages
  • Vertebrochondral (false ribs): 
    • Ribs 8–10
    • Connect indirectly to the sternum via the costal arch
    • The costal cartilages join together to form the costal arch.
    • The costal arch connects to the sternum.
  • Vertebral (false ribs): 
    • Ribs 11–12
    • Also known as floating ribs because the distal end has no attachment

Parts of each rib: 

  • Head: 
    • Articulates with 2 successive thoracic vertebrae
    • Exception: Ribs 1, 10, 11, and 12 articulate with 1 vertebra.
  • Neck
  • Tubercle:
    • Articulates with the transverse process of associated vertebra
    • Exception: Ribs 11 and 12 have no transverse process articulation.
  • Angle
  • Costal groove:
    • Located along the inferior aspect of each rib
    • Contains the intercostal neurovascular bundle

Intercostal spaces:

The spaces between the ribs are the intercostal spaces:

  • The intercostal space height is greater anteriorly than posteriorly.
  • The intercostal space between the upper ribs is greater than the lower ribs.
Anatomy of a rib

Anatomy of a rib

Image by Lecturio.

Sternum

Consists of the following parts:

  • Manubrium:
    • Located at the level of the T3 and T4 vertebral bodies
    • The thickest of the sternum components
    • A palpable landmark is the jugular, or suprasternal, notch.
  • Body (corpus)
  • Xiphoid process: 
    • Cartilaginous in young people
    • Ossified in adulthood
  • Sternal angle: located between the manubrium and the body
Anatomy of the sternum

Anatomy of the sternum

Image by Lecturio.

Intrinsic Muscles

Intrinsic muscles attach only to the thorax. The intrinsic muscles receive blood supply from the intercostal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries and are innervated by the intercostal nerves.

External intercostal muscles:

  • Obliquely oriented
  • Run in an anteroinferior direction from the lower border of the upper rib to the upper border of the lower rib
  • Elevate the ribs during inspiration

Internal intercostal muscles:

  • Obliquely oriented
  • Run in a posteroinferior direction from the lower border of the upper rib to the upper border of the lower rib
  • Depress the ribs during expiration

Innermost intercostal muscles:

  • Separated from internal intercostals by intercostal neurovascular bundles
  • Oriented similarly to the internal intercostals
  • Stabilize intercostal spaces during respiratory movements and assist expiration

Subcostal muscles:

  • Thin muscles found on the inner surface of the posterior thoracic wall 
  • Bridge 2–3 intercostal spaces
  • Pull the ribs inferiorly during forced exhalation and support the thoracic cage

Transversus thoracis muscles:

  • Run from the posterior surface of the lower sternum and xiphoid process to costal cartilages 2–6
  • Depress ribs

Levatores costarum muscles:

  • Run from the transverse processes of C7–T11 to the superior surfaces of the inferior ribs
  • Elevate the rib cage

Serratus posterior muscles:

  • Serratus posterior superior:
    • Runs from the spinous processes of C6–T2 to the costal angle of ribs 2–5
    • Elevates ribs 2–5
  • Serratus posterior inferior:
    • Runs from the spinous processes of T11–L2 to the lower margin of ribs 9–12 
    • Depresses ribs 9–12

Extrinsic muscles

In contrast to the intrinsic muscles, the extrinsic muscles attach to the thorax and other areas of the body.

Pectoralis major muscle:

  • Located on the anterior surface of the thoracic cage
  • Divided into parts:
    • Clavicular part: originates from the anterior surface of the medial half of the clavicle
    • Sternocostal part: originates from the anterior surface of the sternum and costal cartilages 1–6
    • Abdominal part: originates from an anterior layer of the rectus sheath
  • All 3 parts insert into the medial crest of the intertubercular groove.
  • Function: 
    • Arm Arm The arm, or "upper arm" in common usage, is the region of the upper limb that extends from the shoulder to the elbow joint and connects inferiorly to the forearm through the cubital fossa. It is divided into 2 fascial compartments (anterior and posterior). Arm adduction, flexion, extension, and internal rotation
    • Anteroinferior displacement of the scapula
  • Blood supply: pectoral branch of the thoracoacromial trunk
  • Innervation: medial and lateral pectoral nerves
Pectoralis major muscle

Pectoralis major muscle

Image by BioDigital, edited by Lecturio

Pectoralis minor muscle:

  • Runs from ribs 3–5 to the medial border of the coracoid process of the scapula
  • Function:
    • Anteroinferior displacement of the scapula
    • Stabilization of the scapula on the chest wall
  • Blood supply: pectoral branch of the thoracoacromial trunk
  • Innervation: medial pectoral nerve
Extrinsic muscles of the chest wall

Extrinsic muscles of the chest wall

Image by Lecturio.

Serratus anterior muscle:

  • Runs from ribs 1–9 to the anterior surface and medial border of the scapula
  • A “serrated” or “saw-toothed” appearance
  • Function:
    • Anterolateral displacement and rotation of the scapula
    • Stabilization of the scapula against the thoracic wall
  • Blood supply: 
    • Superior and lateral thoracic arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
    • Thoracodorsal artery
  • Innervation: long thoracic nerve
The serratus anterior muscle

Serratus anterior muscle

Image by BioDigital, edited by Lecturio

Subclavius muscle:

  • Runs from the inferior surface of the clavicle to the 1st rib
  • Function: depression of the clavicle and elevation of the 1st rib
  • Blood supply: clavicular branch of the thoracoacromial trunk
  • Innervation: subclavian nerve
The subclavius muscle

Subclavius muscle

Image by BioDigital, edited by Lecturio

Clinical Relevance

  • Pectus excavatum (also known as sunken/funnel chest): the most common congenital deformity of the chest, accounting for 90% of cases. Pectus excavatum is characterized by the abnormal development of several ribs and the sternum, producing a caved-in appearance of the anterior chest wall. Men are predominantly affected (the ratio of men to women is 3:1). The appearance of the defect and the symptoms vary widely. Young individuals are usually asymptomatic. Symptoms may later include chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain and dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea. Treatment is surgical with very good results.
  • Pectus carinatum: the 2nd most common deformity of the chest wall in children (family history in 25% of cases). Associated conditions include Marfan syndrome Marfan syndrome Marfan syndrome is a genetic condition with autosomal dominant inheritance. Marfan syndrome affects the elasticity of connective tissues throughout the body, most notably in the cardiovascular, ocular, and musculoskeletal systems. Marfan Syndrome, Noonan syndrome, mitral valve prolapse Mitral valve prolapse Mitral valve prolapse (MVP) is the most common cardiac valvular defect, and is characterized by bulging of the mitral valve (MV) cusps into the left atrium (LA) during systole. Mitral valve prolapse is most commonly due to idiopathic myxomatous degeneration. Patients are typically asymptomatic. Mitral Valve Prolapse, and congenital heart disease. Individuals may be asymptomatic; however, the disease may lead to cardiorespiratory compromise due to increased rigidity of the chest wall, which impairs normal respiration (especially upon exertion). The result is alveolar hypoventilation and hypoxemia, leading to cor pulmonale Cor Pulmonale Cor pulmonale is right ventricular (RV) dysfunction caused by lung disease that results in pulmonary artery hypertension. The most common cause of cor pulmonale is chronic obstructive pulmonary disease. Dyspnea is the usual presenting symptom. Cor Pulmonale (right heart failure). Emphysema and recurrent respiratory infections are common. Orthotic bracing is the 1st line of treatment and has very good results, especially in younger individuals. 
  • Ankylosing spondylitis Ankylosing spondylitis Ankylosing spondylitis (also known as Bechterew's disease or Marie-Strümpell disease) is a seronegative spondyloarthropathy characterized by chronic and indolent inflammation of the axial skeleton. Severe disease can lead to fusion and rigidity of the spine. Ankylosing Spondylitis: a seronegative spondyloarthropathy characterized by chronic and indolent inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the axial skeleton, which may involve the thoracic spine. Severe disease can lead to fusion and rigidity of the spine. Ankylosing spondylitis Ankylosing spondylitis Ankylosing spondylitis (also known as Bechterew's disease or Marie-Strümpell disease) is a seronegative spondyloarthropathy characterized by chronic and indolent inflammation of the axial skeleton. Severe disease can lead to fusion and rigidity of the spine. Ankylosing Spondylitis is most often seen in young men and is strongly associated with HLA-B27 positivity. Individuals have morning stiffness, decreased range of motion of the spine, and progressive back pain Back pain Back pain is a common complaint among the general population and is mostly self-limiting. Back pain can be classified as acute, subacute, or chronic depending on the duration of symptoms. The wide variety of potential etiologies include degenerative, mechanical, malignant, infectious, rheumatologic, and extraspinal causes. Back Pain, which improves with activity. Most individuals are managed with physical therapy and NSAIDs. Severe cases may require tumor necrosis factor Tumor necrosis factor Tumor necrosis factor (TNF) is a major cytokine, released primarily by macrophages in response to stimuli. The presence of microbial products and dead cells and injury are among the stimulating factors. This protein belongs to the TNF superfamily, a group of ligands and receptors performing functions in inflammatory response, morphogenesis, and cell proliferation. Tumor Necrosis Factor (TNF)-alpha inhibitors or surgery.

References

  1. Cataletto, M.E. (2019). Pectus Carinatum. Medscape. Retrieved August 20, 2021, from https://emedicine.medscape.com/article/1003047-overview
  2. Graeber, G.M., Nazim, M. (2007). The anatomy of the ribs and the sternum and their relationship to chest wall structure and function. Thorac Surg Clin. 17(4), 473–89, vi. https://pubmed.ncbi.nlm.nih.gov/18271162/
  3. Hebra, A. (2018). Pectus Excavatum. Medscape. Retrieved August 20, 2021, from https://emedicine.medscape.com/article/1004953-overview
  4. Kudzinskas, A., Callahan, A.L. (2021). Anatomy, Thorax. Treasure Island (FL): StatPearls Publishing.
  5. Miller, J.I. Jr. (2007). Muscles of the chest wall. Thorac Surg Clin. 17(4), 463–72. https://pubmed.ncbi.nlm.nih.gov/18271161/
  6. Pourtaheri, N. (2016). Chest Wall Anatomy. Medscape. Retrieved August 20, 2021, from https://reference.medscape.com/article/2151800-overview

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