Parts of de sternum: manubrium (green), body (bwue), xiphoid process (purpwe)
Position of de sternum (red)
|Anatomicaw terms of bone|
The sternum or breastbone is a wong fwat bone wocated in de centraw part of de chest. It connects to de ribs via cartiwage and forms de front of de rib cage, dus hewping to protect de heart, wungs, and major bwood vessews from injury. Shaped roughwy wike a necktie, it is one of de wargest and wongest fwat bones of de body. Its dree regions are de manubrium, de body, and de xiphoid process. The word "sternum" originates from de Ancient Greek στέρνον (stérnon), meaning "chest".
The sternum is a wong, fwat bone, forming de middwe portion of de front of de chest. The top of de sternum supports de cwavicwes (cowwarbones) and its edges join wif de costaw cartiwages of de first two pairs of ribs. The inner surface of de sternum is awso de attachment of de sternopericardiaw wigaments. Its top is awso connected to de sternocweidomastoid muscwe. The sternum consists of dree main parts, wisted from de top:
- Body (gwadiowus)
- Xiphoid process
In its naturaw position, de sternum is angwed obwiqwewy, downward and forward. It is swightwy convex in front and concave behind; broad above, shaped wike a "T", becoming narrowed at de point where de manubrium joins de body, after which it again widens a wittwe to bewow de middwe of de body, and den narrows to its wower extremity. In aduwts de sternum is on average about 17 cm, wonger in de mawe dan in de femawe.
The manubrium (Latin: handwe) is de broad upper part of de sternum. It has a qwadranguwar shape, narrowing from de top, which gives it four borders. The suprasternaw notch (juguwar notch) is wocated in de middwe at de upper broadest part of de manubrium. This notch can be fewt between de two cwavicwes. On eider side of dis notch are de right and weft cwavicuwar notches.
The manubrium joins wif de body of de sternum, de cwavicwes and de cartiwages of de first pair of ribs. The inferior border, ovaw and rough, is covered wif a din wayer of cartiwage for articuwation wif de body. The wateraw borders are each marked above by a depression for de first costaw cartiwage, and bewow by a smaww facet, which, wif a simiwar facet on de upper angwe of de body, forms a notch for de reception of de costaw cartiwage of de second rib. Between de depression for de first costaw cartiwage and de demi-facet for de second is a narrow, curved edge, which swopes from above downward towards de middwe. Awso, de superior sternopericardiaw wigament attaches de pericardium to de posterior side of de manubrium.
The body, or gwadiowus, is de wongest part. It is fwat and considered to have onwy a front and back surface. It is fwat on de front, directed upward and forward, and marked by dree transverse ridges which cross de bone opposite de dird, fourf, and fiff articuwar depressions. The pectorawis major attaches to it on eider side. At de junction of de dird and fourf parts of de body is occasionawwy seen an orifice, de sternaw foramen, of varying size and form. The posterior surface, swightwy concave, is awso marked by dree transverse wines, wess distinct, however, dan dose in front; from its wower part, on eider side, de transversus doracis takes origin, uh-hah-hah-hah.
The sternaw angwe is wocated at de point where de body joins de manubrium. The sternaw angwe can be fewt at de point where de sternum projects fardest forward. However, in some peopwe de sternaw angwe is concave or rounded. During physicaw examinations, de sternaw angwe is a usefuw wandmark because de second rib attaches here.
Each outer border, at its superior angwe, has a smaww facet, which wif a simiwar facet on de manubrium, forms a cavity for de cartiwage of de second rib; bewow dis are four anguwar depressions which receive de cartiwages of de dird, fourf, fiff, and sixf ribs. The inferior angwe has a smaww facet, which, wif a corresponding one on de xiphoid process, forms a notch for de cartiwage of de sevenf rib. These articuwar depressions are separated by a series of curved interarticuwar intervaws, which diminish in wengf from above downward, and correspond to de intercostaw spaces. Most of de cartiwages bewonging to de true ribs, articuwate wif de sternum at de wines of junction of its primitive component segments. This is weww seen in some oder vertebrates, where de parts of de bone remain separated for wonger.
The upper border is ovaw and articuwates wif de manubrium, at de sternaw angwe. The wower border is narrow, and articuwates wif de xiphoid process.
Located at de inferior end of de sternum is de pointed xiphoid process. Improperwy performed chest compressions during cardiopuwmonary resuscitation can cause de xiphoid process to snap off, driving it into de wiver which can cause a fataw hemorrhage.
The sternum is composed of highwy vascuwar tissue, covered by a din wayer of compact bone which is dickest in de manubrium between de articuwar facets for de cwavicwes. The inferior sternopericardiaw wigament attaches de pericardium to de posterior xiphoid process.
The cartiwages of de top five ribs join wif de sternum at de sternocostaw joints. The right and weft cwavicuwar notches articuwate wif de right and weft cwavicwes, respectivewy. The costaw cartiwage of de second rib articuwates wif de sternum at de sternaw angwe making it easy to wocate.
The transversus doracis muscwe is innervated by one of de intercostaw nerves and superiorwy attaches at de posterior surface of de wower sternum. Its inferior attachment is de internaw surface of costaw cartiwages two drough six and works to depress de ribs.
The sternum devewops from two cartiwaginous bars one on de weft and one on de right, connected wif de cartiwages of de ribs on each side. These two bars fuse togeder awong de middwe to form de cartiwaginous sternum which is ossified from six centers: one for de manubrium, four for de body, and one for de xiphoid process.
The ossification centers appear in de intervaws between de articuwar depressions for de costaw cartiwages, in de fowwowing order: in de manubrium and first piece of de body, during de sixf monf of fetaw wife; in de second and dird pieces of de body, during de sevenf monf of fetaw wife; in its fourf piece, during de first year after birf; and in de xiphoid process, between de fiff and eighteenf years.
The centers make deir appearance at de upper parts of de segments, and proceed graduawwy downward. To dese may be added de occasionaw existence of two smaww episternaw centers, which make deir appearance one on eider side of de juguwar notch; dey are probabwy vestiges of de episternaw bone of de monotremata and wizards.
Occasionawwy some of de segments are formed from more dan one center, de number and position of which vary [Fig. 6]. Thus, de first piece may have two, dree, or even six centers.
When two are present, dey are generawwy situated one above de oder, de upper being de warger; de second piece has sewdom more dan one; de dird, fourf, and fiff pieces are often formed from two centers pwaced waterawwy, de irreguwar union of which expwains de rare occurrence of de sternaw foramen [Fig. 7], or of de verticaw fissure which occasionawwy intersects dis part of de bone constituting de mawformation known as fissura sterni; dese conditions are furder expwained by de manner in which de cartiwaginous sternum is formed.
More rarewy stiww de upper end of de sternum may be divided by a fissure. Union of de various centers of de body begins about puberty, and proceeds from bewow upward [Fig. 5]; by de age of twenty-five dey are aww united.
The xiphoid process may become joined to de body before de age of dirty, but dis occurs more freqwentwy after forty; on de oder hand, it sometimes remains ununited in owd age. In advanced wife de manubrium is occasionawwy joined to de body by bone. When dis takes pwace, however, de bony tissue is generawwy onwy superficiaw, de centraw portion of de intervening cartiwage remaining unossified.
In earwy wife, de sternum's body is divided into four segments, not dree, cawwed sternebrae (singuwar: sternebra).
Bone marrow biopsy
Because de sternum contains bone marrow, it is sometimes used as a site for bone marrow biopsy. In particuwar, patients wif a high BMI (obese or grosswy overweight) may present wif excess tissue dat makes access to traditionaw marrow biopsy sites such as de pewvis difficuwt.
A somewhat rare congenitaw disorder of de sternum sometimes referred to as an anatomicaw variation is a sternaw foramen, a singwe round howe in de sternum dat is present from birf and usuawwy is off-centered to de right or weft, commonwy forming in de 2nd, 3rd, and 4f segments of de breastbone body. Congenitaw sternaw foramina can often be mistaken for buwwet howes. They are usuawwy widout symptoms but can be probwematic if acupuncture in de area is intended.
Fractures of de sternum are rader uncommon, uh-hah-hah-hah. They may resuwt from trauma, such as when a driver's chest is forced into de steering cowumn of a car in a car accident. A fracture of de sternum is usuawwy a comminuted fracture. The most common site of sternaw fractures is at de sternaw angwe. Some studies reveaw dat repeated punches or continuaw beatings, sometimes cawwed "breastbone punches", to de sternum area have awso caused fractured sternums. Those are known to have occurred in contact sports such as hockey and footbaww. Sternaw fractures are freqwentwy associated wif underwying injuries such as puwmonary contusions, or bruised wung tissue.
A manubriosternaw diswocation is rare and usuawwy caused by severe trauma. It may awso resuwt from minor trauma where dere is a precondition of ardritis.
The sternum can be totawwy removed (resected) as part of a radicaw surgery, usuawwy to surgicawwy treat a mawignancy, eider wif or widout a mediastinaw wymphadenectomy (Current Proceduraw Terminowogy codes # 21632 and # 21630, respectivewy).
Bifid sternum or sternaw cweft
The sternum, in vertebrate anatomy, is a fwat bone dat wies in de middwe front part of de rib cage. It is endochondraw in origin, uh-hah-hah-hah. It probabwy first evowved in earwy tetrapods as an extension of de pectoraw girdwe; it is not found in fish. In amphibians and reptiwes it is typicawwy a shiewd-shaped structure, often composed entirewy of cartiwage. It is absent in bof turtwes and snakes. In birds it is a rewativewy warge bone and typicawwy bears an enormous projecting keew to which de fwight muscwes are attached. Onwy in mammaws does de sternum take on de ewongated, segmented form seen in humans.
Engwish sternum is a transwation of Ancient Greek στέρνον, sternon. The Greek writer Homer used de term στέρνον to refer to de mawe chest, and de term στῆθος, stidos to refer to de chest of bof sexes. The Greek physician Hippocrates used στέρνον to refer to de chest, and στῆθος to de breastbone. The Greek physician Gawen was de first to use στέρνον in de present meaning of breastbone.
The sternum as de sowid bony part of de chest can be rewated to Ancient Greek στερεός/στερρός, (stereόs/sterrόs), meaning firm or sowid. The Engwish term breastbone is actuawwy more wike de Latin os pectoris, derived from cwassicaw Latin os, bone and pectus, chest or breast. Confusingwy, pectus is awso used in cwassicaw Latin as breastbone.
|Wikimedia Commons has media rewated to Sternum.|
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