| Rib cage | |
|---|---|
 Human rib cage | |
 Animation of the rib cage | |
| Details | |
| Identifiers | |
| Latin | cavea thoracis |
| MeSH | D000070602 |
| TA98 | A02.3.04.001 |
| TA2 | 1096 |
| FMA | 7480 |
| Anatomical terminology | |
Therib cage orthoracic cage is anendoskeletal enclosure in thethorax of mostvertebrates that comprises theribs,vertebral column andsternum, which protect thevital organs of thethoracic cavity, such as theheart,lungs andgreat vessels and support theshoulder girdle to form thecore part of theaxial skeleton.
A typicalhuman thoracic cage consists of 12 pairs of ribs and the adjoiningcostal cartilages, the sternum (along with themanubrium andxiphoid process), and the 12thoracic vertebrae articulating with the ribs. The thoracic cage also provides attachments for extrinsicskeletal muscles of theneck,upper limbs,upper abdomen andback, and together with the overlyingskin and associatedfascia andmuscles, makes up thethoracic wall.
Intetrapods, the rib cage intrinsically holds themuscles of respiration (diaphragm,intercostal muscles, etc.) that are crucial for activeinhalation and forcedexhalation, and therefore has a majorventilatory function in therespiratory system.
There are thirty-three vertebrae in the human vertebral column. The rib cage is associated with TH1−TH12. Ribs are described based on their location and connection with the sternum. All ribs are attached posteriorly to thethoracic vertebrae and are numbered accordingly one to twelve. Ribs that articulate directly with the sternum are calledtrue ribs, whereas those that do not articulate directly are termedfalse ribs. Thefalse ribs include thefloating ribs (eleven and twelve) that are not attached to the sternum at all.
The termstrue ribs andfalse ribs describe rib pairs that are directly or indirectly attached to thesternum respectively. The first seven rib pairs known as thefixed orvertebrosternal ribs are thetrue ribs (Latin:costae verae) as they connect directly to the sternum via their own individualcostal cartilages. The next five pairs (eighth to twelfth) are thefalse ribs (Latin:costae spuriae) orvertebrochondral ribs, which do not connect directly to the sternum. The first three pairs of vertebrochondral ribs (eighth to tenth) connect indirectly to the sternum via the costal cartilages of the ribs above them,[1][2] and the overall elasticity of their articulations allows thebucket handle movements of the rib cage essential for respiratory activity.
The phrasefloating rib (Latin:costae fluctuantes) orvertebral rib refers to the two lowermost (the eleventh and twelfth) rib pairs; so-called because they are attached only to thevertebrae and not to the sternum or any of the costal cartilages. These ribs are relatively small and delicate, and include a cartilaginous tip.[3]
The spaces between the ribs are known asintercostal spaces; they contain the instrinsicintercostal muscles and theneurovascular bundles containingintercostal nerves,arteries andveins.[4] The superficial surface of the rib cage is covered by thethoracolumbar fascia, which provides external attachments for theneck,back,pectoral andabdominal muscles.
Each rib consists of a head, neck, and a shaft. All ribs are attached posteriorly to thethoracic vertebrae. They are numbered to match the vertebrae they attach to – one to twelve, from top (T1) to bottom. The head of the rib is the end part closest to thevertebra with which itarticulates. It is marked by a kidney-shaped articular surface which is divided by a horizontal crest into two articulating regions. The upper region articulates with theinferior costal facet on the vertebra above, and the larger region articulates with thesuperior costal facet on the vertebra with the same number. Thetransverse process of a thoracic vertebra also articulates at thetransverse costal facet with the tubercle of the rib of the same number. The crest gives attachment to theintra-articular ligament.[5]
The neck of the rib is the flattened part that extends laterally from the head. The neck is about 3 cm long. Its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck. Its upper border presents a rough crest (crista colli costae) for the attachment of the anteriorcostotransverse ligament; its lower border is rounded.
On the posterior surface at the neck, is an eminence—the tubercle that consists of an articular and a non-articular portion. The articular portion is the lower and more medial of the two and presents a small, oval surface for articulation with thetransverse costal facet on the end of the transverse process of the lower of the two vertebrae to which the head is connected. The non-articular portion is a rough elevation and affords attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper ribs than in the lower ribs.
The angle of arib (costal angle) may both refer to the bending part of it, and a prominent line in this area, a little in front of the tubercle. This line is directed downward and laterally; this gives attachment to a tendon of theiliocostalis muscle. At this point, the rib is bent in two directions, and at the same time twisted on its long axis.
The distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The area between the angle and the tubercle is rounded, rough, and irregular, and serves for the attachment of thelongissimus dorsi muscle.
Thefirst rib (the topmost one) is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward, and its borders inward and outward.
Thehead is small and rounded, and possesses only a single articular facet, for articulation with the body of the firstthoracic vertebra. Theneck is narrow and rounded. Thetubercle, thick and prominent, is placed on the outer border. It bears a small facet for articulation with thetransverse costal facet on the transverse process of T1. There is noangle, but at the tubercle, the rib is slightly bent, with the convexity upward, so that the head of the bone is directed downward. The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, thescalene tubercle, for the attachment of theanterior scalene; theanterior groove transmits thesubclavian vein, theposteriorthesubclavian artery and the lowest trunk of thebrachial plexus. Behind the posterior groove is a rough area for the attachment of themedial scalene. Theunder surface is smooth and without a costal groove. Theouter border is convex, thick, and rounded, and at its posterior part gives attachment to the first digitation of theserratus anterior. Theinner border is concave, thin, and sharp, and marked about its center by the scalene tubercle. Theanterior extremity is larger and thicker than that of any of the other ribs.
Thesecond rib is the second uppermost rib in humans or second most frontal in animals that walk on four limbs. In humans, the second rib is defined as a true rib since it connects with the sternum through the intervention of thecostal cartilage anteriorly (at the front). Posteriorly, the second rib is connected with thevertebral column by thesecond thoracic vertebra. The second rib is much longer than thefirst rib, but has a very similar curvature. The non-articular portion of the tubercle is occasionally only feebly marked. The angle is slight and situated close to the tubercle. The body is not twisted so that both ends touch any plane surface upon which it may be laid; but there is a bend, with its convexity upward, similar to, though smaller than that found in the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex, and looks upward and a little outward; near the middle of it is a rough eminence for the origin of the lower part of the first and the whole of the second digitation of the serratus anterior; behind and above this is attached theposterior scalene. The internal surface, smooth, and concave, is directed downward and a little inward: on its posterior part there is a short costal groove between the ridge of the internal surface of the rib and the inferior border. It protects the intercostal space containing theintercostal veins,intercostal arteries, andintercostal nerves.[6][4]
Theninth rib has a frontal part at the same level as thefirst lumbar vertebra. This level is called thetranspyloric plane, since thepylorus is also at this level.[7]
Thetenth rib attaches directly to the body of vertebra T10 instead of between vertebrae like the second through ninth ribs. Due to this direct attachment, vertebra T10 has a complete costal facet on its body.[3]
Theeleventh and twelfth ribs, thefloating ribs, have a singlearticular facet on the head, which is of rather large size. They have no necks or tubercles, and are pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove, whereas the twelfth does not. The twelfth rib is much shorter than the eleventh rib, and only has a one articular facet.[8]
The sternum is a long,flat bone that forms the front of the rib cage. The cartilages of the top seven ribs (thetrue ribs) join with the sternum at the sternocostal joints. The costal cartilage of the second rib articulates with the sternum at the sternal angle making it easy to locate.[9]
The manubrium is the wider, superior portion of the sternum. The top of the manubrium has a shallow, U-shaped border called the jugular (suprasternal) notch. The clavicular notch is the shallow depression located on either side at the superior-lateral margins of the manubrium. This is the site of thesternoclavicular joint, between the sternum and clavicle. The first ribs also attach to the manubrium.[10]
Thetransversus thoracis muscle is innervated by one of theintercostal 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.[11]
Expansion of the rib cage in males is caused by the effects oftestosterone during puberty.[12] Thus, males generally have broad shoulders and expanded chests, allowing them to inhale more air to supply their muscles with oxygen.
The development of the rib cage is influenced by a combination of genetic and environmental factors, as well as specific stages of embryonic growth.Genetic factors play a critical role, with specific genes regulating the formation of bones and cartilage to ensure the proper development and alignment of the ribs and sternum. During theembryonic stage, the rib cage begins to form from the mesoderm, one of the three primary germ layers. Ribs develop from structures called somites, which later segment into vertebrae and ribs. Initially, the ribs are composed ofcartilage, which gradually ossifies into bone through a process known as endochondral ossification.
As the embryo grows, the ribs elongate and differentiate into three types:true ribs, which attach directly to the sternum;false ribs, which connect to the sternum via cartilage; andfloating ribs, which do not attach to the sternum. Additionally,environmental factors such as maternal health, nutrition, and exposure to certain substances can impact rib cage development. For instance, deficiencies in essential nutrients like calcium and vitamin D may hinder proper bone growth and development. Together, these genetic, developmental, and environmental influences ensure the formation of a functional rib cage.
Variations in the number of ribs occur. About 1 in 200–500 people have an additionalcervical rib, and there is a female predominance.[13] Intrathoracic supernumerary ribs are extremely rare.[14] The rib remnant of the7th cervical vertebra on one or both sides is occasionally replaced by a free extra rib called acervical rib, which can mechanically interfere with the nerves (brachial plexus) going to the arm.
In several ethnic groups, most significantly the Japanese, the tenth rib is sometimes afloating rib, as it lacks a cartilaginous connection to the seventh rib.[3]
The human rib cage is a component of the humanrespiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the musculardiaphragm, at the floor of the thoracic cavity, contracts and flattens, while the contraction ofintercostal muscles lift the rib cage up and out.
Expansion of the thoracic cavity is driven in three planes; the vertical, the anteroposterior and the transverse. The vertical plane is extended by the help of the diaphragm contracting and the abdominal muscles relaxing to accommodate the downward pressure that is supplied to the abdominal viscera by the diaphragm contracting. A greater extension can be achieved by the diaphragm itself moving down, rather than simply the domes flattening. The second plane is the anteroposterior and this is expanded by a movement known as the 'pump handle'. The downward sloping nature of the upper ribs are as such because they enable this to occur. When the external intercostal muscles contract and lift the ribs, the upper ribs are able also to push the sternum up and out. This movement increases the anteroposterior diameter of the thoracic cavity, and hence aids breathing further. The third, transverse, plane is primarily expanded by the lower ribs (some say it is the 7th to 10th ribs in particular), with the diaphragm's central tendon acting as a fixed point. When the diaphragm contracts, the ribs are able to evert (meaning turn outwards or inside out) and produce what is known as thebucket handle movement, facilitated by gliding at thecostovertebral joints. In this way, the transverse diameter is expanded and the lungs can fill.
The circumference of the normal adult human rib cage expands by 3 to 5 cm during inhalation.[15]
Rib fractures are the most common injury to the rib cage. These most frequently affect the middle ribs. When several adjacent ribs incur two or more fractures each, this can result in aflail chest which is a life-threatening condition.
A dislocated rib can be painful and can be caused simply by coughing, or for example by trauma or lifting heavy weights.[16]
One or more costal cartilages can become inflamed – a condition known ascostochondritis; the resulting pain is similar to that of a heart attack.
Abnormalities of the rib cage includepectus excavatum ("sunken chest") andpectus carinatum ("pigeon chest"). Abifid rib is a bifurcated rib, split towards the sternal end, and usually just affecting one of the ribs of a pair. It is acongenital defect affecting about 1.2% of the population. It is often without symptoms though respiratory difficulties and other problems can arise.
Rib removal is the surgical removal of one or more ribs for therapeutic or cosmetic reasons.
Rib resection is the removal of part of a rib.
The ability of the human rib to regenerate itself has been appreciated for some time.[2][5] However, the repair has only been described in a few case reports. The phenomenon has been appreciated particularly by craniofacial surgeons, who use both cartilage and bone material from the rib for ear, jaw, face, and skull reconstruction.[6][8]
The perichondrium and periosteum are fibrous sheaths of vascular connective tissue surrounding the rib cartilage and bone respectively. These tissues containing a source of progenitor stem cells that drive regeneration.[1][17][18]
The position of ribs can be permanently altered by a form ofbody modification calledtightlacing, which uses acorset to compress and move the ribs.
The ribs, particularly their sternal ends, are used as a way of estimating age inforensic pathology due to their progressive ossification.[19]
The number of ribs as 24 (12 pairs) was noted by theFlemishanatomistVesalius in his key work of anatomyDe humani corporis fabrica in 1543, setting off a wave of controversy, as it was traditionally assumed from the Biblical story ofAdam and Eve that men's ribs would number one fewer than women's.[20][21] However, thirteenth or "cervical ribs" occur in 1% of humans[12] and this is more common in females than in males.[13]
Inherpetology, costal grooves refer to lateral indents along the integument ofsalamanders. The grooves run between theaxilla to thegroin. Each groove overlies the myotomal septa to mark the position of the internal rib.[22][23]
Birds andreptiles have bonyuncinate processes on their ribs that project caudally from the vertical section of each rib.[24] These serve to attachsacral muscles and also aid in allowing greater inspiration.Crocodiles have cartilaginous uncinate processes.
This article incorporates text in thepublic domain from the 20th edition ofGray's Anatomy(1918)
This article incorporatestext available under theCC BY 4.0 license.Betts, J Gordon; Desaix, Peter; Johnson, Eddie; Johnson, Jody E; Korol, Oksana; Kruse, Dean; Poe, Brandon; Wise, James; Womble, Mark D; Young, Kelly A (May 14, 2023).Anatomy & Physiology. Houston: OpenStax CNX. 7.4 The Thoracic Cage.ISBN 978-1-947172-04-3.
{{cite web}}: CS1 maint: archived copy as title (link)Although many people might think that males have fewer ribs than females—most likely sparked by the biblical story of Adam and Eve—there is no factual evidence.
