The sternum or breastbone is a long
flat bone
Flat bones are bones whose principal function is either extensive protection or the provision of broad surfaces for muscular attachment. These bones are expanded into broad, flat plates,''Gray's Anatomy'' (1918). (See infobox) as in the cranium ...
located in the central part of the
chest
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
. It connects to the
ribs via
cartilage and forms the front of the
rib cage
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a sem ...
, thus helping to protect the
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...
,
lungs
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side ...
, and major
blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s from injury. Shaped roughly like a
necktie, it is one of the largest and longest flat bones of the body. Its three regions are the manubrium, the body, and the
xiphoid process
The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Bo ...
.
The word "sternum" originates from the Ancient Greek στέρνον (stérnon), meaning "chest".
Structure
The sternum is a narrow,
flat bone
Flat bones are bones whose principal function is either extensive protection or the provision of broad surfaces for muscular attachment. These bones are expanded into broad, flat plates,''Gray's Anatomy'' (1918). (See infobox) as in the cranium ...
, forming the middle portion of the front of the
chest
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
. The top of the sternum supports the
clavicles
The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the right ...
(collarbones) and its edges join with the
costal cartilage
The costal cartilages are bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax. Costal cartilage is only found at the anterior ends of the ribs, providing medial extension.
...
s of the first two pairs of
ribs. The inner surface of the sternum is also the attachment of the
sternopericardial ligaments
The fibrous pericardium is attached to the posterior surface of the sternum by the superior and inferior sternopericardiac ligaments (sternopericardial ligaments); the upper passing to the manubrium, and the lower to the xiphoid process
The xi ...
. Its top is also connected to the
sternocleidomastoid muscle
The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck. The sternocleidomastoid is innervated by the access ...
. The sternum consists of three main parts, listed from the top:
* Manubrium
* Body (gladiolus)
*
Xiphoid process
The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Bo ...
In its natural position, the sternum is angled obliquely, downward and forward. It is slightly convex in front and concave behind; broad above, shaped like a "T", becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. In adults the sternum is on average about 17 cm, longer in the male than in the female.
Manubrium
![Manubrium - animation](https://upload.wikimedia.org/wikipedia/commons/6/61/Manubrium_-_animation.gif)
The manubrium (
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
for "handle") is the broad upper part of the sternum. It has a
quadrangular
Quadrangle or The Quadrangle may refer to:
Architecture
* Quadrangle (architecture), a courtyard surrounded by a building or several buildings, often at a college
Various specific quadrangles, often called "the quad" or "the quadrangle":
North ...
shape, narrowing from the top, which gives it four borders. The
suprasternal notch
The suprasternal notch, also known as the fossa jugularis sternalis, jugular notch, or Plender gap, is a large, visible dip in between the neck in humans, between the clavicles, and above the manubrium of the sternum.
Structure
The suprasternal ...
(jugular notch) is located in the middle at the upper broadest part of the manubrium. This notch can be felt between the two
clavicles
The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the right ...
. On either side of this notch are the right and left
clavicular notches.
[
The manubrium joins with the body of the sternum, the clavicles and the cartilages of the first pair of ribs. The inferior border, oval and rough, is covered with a thin layer of cartilage for articulation with the body. The lateral borders are each marked above by a depression for the first ]costal cartilage
The costal cartilages are bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax. Costal cartilage is only found at the anterior ends of the ribs, providing medial extension.
...
, and below by a small facet, which, with a similar facet on the upper angle of the body, forms a notch for the reception of the costal cartilage of the second rib. Between the depression for the first costal cartilage and the demi-facet for the second is a narrow, curved edge, which slopes from above downward towards the middle. Also, the superior sternopericardial ligament attaches the pericardium
The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made o ...
to the posterior side of the manubrium.
Body
The body, or gladiolus, is the longest sternal part. It is flat and considered to have only a front and back surface. It is flat on the front, directed upward and forward, and marked by three transverse ridges which cross the bone opposite the third, fourth, and fifth articular depressions. The pectoralis major attaches to it on either side. At the junction of the third and fourth parts of the body is occasionally seen an orifice, the sternal foramen, of varying size and form. The posterior surface, slightly concave, is also marked by three transverse lines, less distinct, however, than those in front; from its lower part, on either side, the transversus thoracis
The transversus thoracis muscle (), also known as triangularis sterni, lies internal to the thoracic cage, anteriorly. It is usually a thin plane of muscular and tendinous fibers, however on athletic individuals it can be a thick 'slab of meat', ...
takes origin.
The sternal angle is located at the point where the body joins the manubrium. The sternal angle can be felt at the point where the sternum projects farthest forward. However, in some people the sternal angle is concave or rounded. During physical examinations, the sternal angle is a useful landmark because the second rib attaches here.[
Each outer border, at its superior angle, has a small facet, which with a similar facet on the manubrium, forms a cavity for the cartilage of the second rib; below this are four angular depressions which receive the cartilages of the third, fourth, fifth, and sixth ribs. The inferior angle has a small facet, which, with a corresponding one on the xiphoid process, forms a notch for the cartilage of the seventh rib. These articular depressions are separated by a series of curved interarticular intervals, which diminish in length from above downward, and correspond to the intercostal spaces. Most of the cartilages belonging to the ]true rib
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a semi-r ...
s, articulate with the sternum at the lines of junction of its primitive component segments. This is well seen in some other vertebrates, where the parts of the bone remain separated for longer.
The upper border is oval and articulates with the manubrium, at the sternal angle. The lower border is narrow, and articulates with the xiphoid process
The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Bo ...
.
Xiphoid process
Located at the inferior end of the sternum is the pointed xiphoid process
The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Bo ...
. Improperly performed chest compressions during cardiopulmonary resuscitation
Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore spon ...
can cause the xiphoid process to snap off, driving it into the liver which can cause a fatal hemorrhage.[
The sternum is composed of highly ]vascular
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
tissue, covered by a thin layer of compact bone which is thickest in the manubrium between the articular facets for the clavicles
The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the right ...
. The inferior sternopericardial ligament attaches the pericardium to the posterior xiphoid process.
Joints
The cartilages of the top five ribs join with the sternum at the sternocostal joints. The right and left clavicular notches articulate with the right and left clavicles, respectively. The costal cartilage of the second rib articulates with the sternum at the sternal angle making it easy to locate.
The transversus thoracis
The transversus thoracis muscle (), also known as triangularis sterni, lies internal to the thoracic cage, anteriorly. It is usually a thin plane of muscular and tendinous fibers, however on athletic individuals it can be a thick 'slab of meat', ...
muscle is innervated by one of the intercostal nerves and superiorly attaches at the posterior surface of the lower sternum. Its inferior attachment is the internal surface of costal cartilages two through six and works to depress the ribs.
Development
The sternum develops from two cartilaginous bars one on the left and one on the right, connected with the cartilages of the ribs on each side. These two bars fuse together along the middle to form the cartilaginous sternum which is ossified from six centers: one for the manubrium, four for the body, and one for the xiphoid process
The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Bo ...
.
The ossification
Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in ...
centers appear in the intervals between the articular depressions for the costal cartilages
The costal cartilages are bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax. Costal cartilage is only found at the anterior ends of the ribs, providing medial extension.
...
, in the following order: in the manubrium and first piece of the body, during the sixth month of fetal life; in the second and third pieces of the body, during the seventh month of fetal life; in its fourth piece, during the first year after birth; and in the xiphoid process, between the fifth and eighteenth years.
The centers make their appearance at the upper parts of the segments, and proceed gradually downward. To these may be added the occasional existence of two small ''episternal'' centers, which make their appearance one on either side of the jugular notch
The suprasternal notch, also known as the fossa jugularis sternalis, jugular notch, or Plender gap, is a large, visible dip in between the neck in humans, between the clavicles, and above the manubrium of the sternum.
Structure
The suprasternal ...
; they are probably vestiges of the episternal bone of the monotremata and lizards.
Occasionally some of the segments are formed from more than one center, the number and position of which vary ig. 6 Thus, the first piece may have two, three, or even six centers.
When two are present, they are generally situated one above the other, the upper being the larger; the second piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two centers placed laterally, the irregular union of which explains the rare occurrence of the sternal foramen ig. 7 or of the vertical fissure which occasionally intersects this part of the bone constituting the malformation known as ''fissura sterni;'' these conditions are further explained by the manner in which the cartilaginous sternum is formed.
More rarely still the upper end of the sternum may be divided by a fissure
A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes.
Ground fissure
...
. Union of the various centers of the body begins about puberty
Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a bo ...
, and proceeds from below upward ig. 5 by the age of 25 they are all united.
The xiphoid process may become joined to the body before the age of thirty, but this occurs more frequently after forty; on the other hand, it sometimes remains ununited in old age. In advanced life the manubrium is occasionally joined to the body by bone. When this takes place, however, the bony tissue is generally only superficial, the central portion of the intervening cartilage remaining unossified.
In early life, the sternum's body is divided into four segments, not three, called ''sternebrae'' (singular: ''sternebra'').
Variations
In 2.5–13.5% of the population, a foramen known as sternal foramen may be presented at the lower third of the sternal body. In extremely rare cases, multiple foramina may be observed. Fusion of the manubriosternal joint also occurs in around 5% of the population. Small ossicles known as episternal ossicles may also be present posterior to the superior end of the manubrium. Another variant called suprasternal tubercle is formed when the episternal ossicles fuse with the manubrium.
Clinical significance
Bone marrow biopsy
Because the sternum contains bone marrow, it is sometimes used as a site for bone marrow biopsy
Bone marrow examination refers to the pathologic analysis of samples of bone marrow obtained by bone marrow biopsy (often called trephine biopsy) and bone marrow aspiration. Bone marrow examination is used in the diagnosis of a number of conditio ...
. In particular, patients with a high BMI (obese or grossly overweight) may present with excess tissue that makes access to traditional marrow biopsy sites such as the pelvis difficult.
Sternal opening
A somewhat rare congenital disorder
A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities ca ...
of the sternum sometimes referred to as an anatomical variation
An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categ ...
is a sternal foramen, a single round hole in the sternum that is present from birth and usually is off-centered to the right or left, commonly forming in the 2nd, 3rd, and 4th segments of the breastbone body. Congenital sternal foramina can often be mistaken for bullet holes. They are usually without symptoms but can be problematic if acupuncture in the area is intended.
Fractures
Fractures of the sternum are rather uncommon. They may result from trauma, such as when a driver's chest is forced into the steering column
The automotive steering column is a device intended primarily for connecting the steering wheel to the steering mechanism.
Secondary functions
A steering column may also perform the following secondary functions:
*energy dissipation management ...
of a car in a car accident. A fracture of the sternum is usually a comminuted fracture. The most common site of sternal fractures is at the sternal angle. Some studies reveal that repeated punches or continual beatings, sometimes called "breastbone punches", to the sternum area have also caused fractured sternums. Those are known to have occurred in contact sports such as hockey and football. Sternal fractures are frequently associated with underlying injuries such as pulmonary contusion
A pulmonary contusion, also known as lung contusion, is a bruise of the lung, caused by chest trauma. As a result of damage to capillaries, blood and other fluids accumulate in the lung tissue. The excess fluid interferes with gas exchange, po ...
s, or bruised lung tissue.
Dislocation
A manubriosternal dislocation is rare and usually caused by severe trauma. It may also result from minor trauma where there is a precondition of arthritis.
Sternotomy
The breastbone is sometimes cut open (a median sternotomy
Median sternotomy is a type of surgical procedure in which a vertical inline incision is made along the sternum, after which the sternum itself is divided using a sternal saw. This procedure provides access to the heart and lungs for surgical pro ...
) to gain access to the thoracic contents when performing cardiothoracic surgery
Cardiothoracic surgery is the field of medicine involved in surgical treatment of organs inside the thoracic cavity — generally treatment of conditions of the heart (heart disease), lungs ( lung disease), and other pleural or mediastinal str ...
.
Resection
The sternum can be totally removed (resected) as part of a radical surgery, usually to surgically treat a malignancy, either with or without a mediastinal lymphadenectomy
Lymphadenectomy or lymph node dissection is the surgical removal of one or more groups of lymph nodes. It is almost always performed as part of the surgical management of cancer. In a regional lymph node dissection, some of the lymph nodes in the ...
( Current Procedural Terminology codes # 21632 and # 21630, respectively).
Bifid sternum or sternal cleft
A bifid sternum is an extremely rare congenital abnormality caused by the fusion failure of the sternum. This condition results in sternal cleft which can be observed at birth without any symptom.
Other animals
The sternum, in vertebrate anatomy, is a flat bone
Flat bones are bones whose principal function is either extensive protection or the provision of broad surfaces for muscular attachment. These bones are expanded into broad, flat plates,''Gray's Anatomy'' (1918). (See infobox) as in the cranium ...
that lies in the middle front part of the rib cage
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a sem ...
. It is endochondral in origin. It probably first evolved in early tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
s as an extension of the pectoral girdle
The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of ...
; it is not found in fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...
. In amphibians and reptiles it is typically a shield-shaped structure, often composed entirely of cartilage. It is absent in both turtle
Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...
s and snake
Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
s. In bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s it is a relatively large bone and typically bears an enormous projecting keel
The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...
to which the flight muscles are attached. Only in mammals does the sternum take on the elongated, segmented form seen in humans.
Arthropods
In arachnid
Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegar ...
s, the sternum is the ventral (lower) portion of the cephalothorax. It consists of a single sclerite
A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...
situated between the coxa, opposite the carapace.
Etymology
English ''sternum'' is a translation of Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...
, '.[Triepel, H. (1910). ''Die anatomischen Namen. Ihre Ableitung und Aussprache. Mit einem Anhang: Biographische Notizen.''(Dritte Auflage). Wiesbaden: Verlag J.F. Bergmann.] The Greek writer Homer
Homer (; grc, Ὅμηρος , ''Hómēros'') (born ) was a Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Homer is considered one of the ...
used the term to refer to the ''male chest'',[Hyrtl, J. (1880). ''Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart.'' Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler.][Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press.] and the term , ' to refer to the ''chest of both sexes''. The Greek physician
A physician (American English), medical practitioner (Commonwealth English), medical doctor, or simply doctor, is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through th ...
Hippocrates
Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek physician of the classical period who is considered one of the most outstanding figures in the history o ...
used στέρνον to refer to the ''chest'', and στῆθος to the ''breastbone''. The Greek physician Galen
Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one ...
was the first to use in the present meaning of ''breastbone''.
The sternum as the solid bony part of the chest[Kraus, L.A. (1844). ''Kritisch-etymologisches medicinisches Lexikon'' (Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.] can be related to Ancient Greek , ''()'', meaning ''firm'' or ''solid''. The English term breastbone is actually more like the Latin ''os pectoris'',[Schreger, C.H.Th. (1805). ''Synonymia anatomica. Synonymik der anatomischen Nomenclatur.'' Fürth: im Bureau für Literatur.][Siebenhaar, F.J. (1850). ''Terminologisches Wörterbuch der medicinischen Wissenschaften.'' (Zweite Auflage). Leipzig: Arnoldische Buchhandlung.] derived from classical Latin ''os'', bone[Lewis, C.T. & Short, C. (1879). ''A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary.'' Oxford: Clarendon Press.] and ''pectus'', chest or breast. Confusingly, ''pectus'' is also used in classical Latin as ''breastbone''.
Additional images
File:Sternum animation3.gif, Position of sternum (shown in red). Animation.
File:Sobo 1909 31.png, Sternum seen posteriorly
File:Sobo 1909 181.png, Sternum cut along the frontal plane showing interior of the bone
File:Sobo 1909 32.png, Sternum, lateral aspect
File:Sternum location.png, Position of the sternum the thoracic cage
File:Sternum.gif, Computer-generated image of ribcage turntable highlighting the sternum
File:Sternum Anatomy by Jason Christian.webm, Sternum anatomy
See also
*Pectus carinatum
Pectus carinatum, also called pigeon chest, is a malformation of the chest characterized by a protrusion of the sternum and ribs. It is distinct from the related malformation pectus excavatum.
Signs and symptoms
People with pectus carinatum usua ...
*Pectus excavatum
Pectus excavatum is a structural deformity of the anterior thoracic wall in which the sternum and rib cage are shaped abnormally. This produces a caved-in or sunken appearance of the chest. It can either be present at birth or develop after pubert ...
References
External links
*
{{Authority control
Bones of the thorax
Flat bones