Theclavicle,collarbone, orkeybone is a slender, S-shapedlong bone approximately 6 inches (15 cm) long[1] that serves as astrut between theshoulder blade and thesternum (breastbone). There are two clavicles, one on each side of the body. The clavicle is the only long bone in the body that lies horizontally.[2] Together with the shoulder blade, it makes up theshoulder girdle. It is a palpable bone and, in people who have lessfat in this region, the location of the bone is clearly visible. It receives its name fromLatinclavicula 'little key' because the bone rotates along its axis like a key when the shoulder isabducted. The clavicle is the most commonly fractured bone. It can easily be fractured by impacts to the shoulder from the force of falling on outstretched arms or by a direct hit.[3]
The collarbone is a thin doubly curvedlong bone that connects thearm to thetrunk of the body.[4] Located directly above thefirst rib, it acts as astrut to keep the scapula in place so that the arm can hang freely. At its rounded medial end (sternal end), it articulates with themanubrium of thesternum (breastbone) at thesternoclavicular joint. At its flattened lateral end (acromial end), it articulates with theacromion, a process of thescapula (shoulder blade), at theacromioclavicular joint.
Right clavicle—from below, and from above
Left clavicle—from above, and from below
The rounded medial region (sternal region) of the shaft has a long curve laterally and anteriorly along two-thirds of the entire shaft. The flattened lateral region (acromial region) of the shaft has an even larger posterior curve to articulate with the acromion of the scapula. The medial region is the longest clavicular region as it takes up two-thirds of the entire shaft. The lateral region is both the widest clavicular region and thinnest clavicular region. The lateral end has a rough inferior surface that bears a ridge, thetrapezoid line, and a slight rounded projection, theconoid tubercle (above thecoracoid process). These surface features are attachment sites for muscles and ligaments of the shoulder.
It can be divided into three parts: medial end, lateral end, and shaft.
The medial end is also known as the sternal end. It is quadrangular and articulates with the clavicular notch of themanubrium of thesternum to form thesternoclavicular joint.[5] The articular surface extends to the inferior aspect for articulation with the firstcostal cartilage.
The lateral end is also known as the acromial end. It is flat from above downward. It bears a facet that articulates with the shoulder to form theacromioclavicular joint. The area surrounding the joint gives an attachment to the joint capsule. The anterior border is concave forward and the posterior border is convex backward.[6]
The shaft is divided into two main regions, the medial region, and the lateral region. The medial region is also known as the sternal region, it is the longest clavicular region as it takes up two-thirds of the entire shaft. The lateral region is also known as the acromial region, it is both the widest clavicular region and thinnest clavicular region.
The lateral region of the shaft has two borders and two surfaces.
the anterior border is concave forward and gives origin to thedeltoid muscle.
the posterior border is convex and gives attachment to thetrapezius muscle.
the inferior surface has a ridge called thetrapezoid line and a tubercle; the conoid tubercle for attachment with the trapezoid and theconoid ligament, part of thecoracoclavicular ligament that serves to connect the collarbone with the coracoid process of the scapula.
The collarbone is the first bone to begin the process ofossification (laying down of minerals onto a preformed matrix) duringdevelopment of the embryo, during the fifth and sixth weeks ofgestation. However, it is one of the last bones to finish ossification at about 21–25 years of age. Its lateral end is formed byintramembranous ossification while medially it is formed byendochondral ossification. It consists of a mass ofcancellous bone surrounded by acompact bone shell. The cancellous bone forms via twoossification centres, one medial and one lateral, which fuse later on. The compact forms as the layer offascia covering the bone stimulate the ossification of adjacent tissue. The resulting compact bone is known as a periosteal collar.
The shape of the clavicle varies more than most other long bones. It is occasionally pierced by a branch of thesupraclavicular nerve. In males the clavicle is usually longer and larger than in females. A study measuring 748 males and 252 females saw a difference in collarbone length between age groups 18–20 and 21–25 of about 6 and 5 mm (0.24 and 0.20 in) for males and females respectively.[9]
The left clavicle is usually longer and weaker than the right clavicle.[8][10]
Thelevator claviculae muscle, present in 2–3% of people, originates on the transverse processes of the upper cervical vertebrae and is inserted in the lateral half of the clavicle.
It serves as a rigid support from which the scapula and free limb are suspended; an arrangement that keeps the upper limb away from the thorax so that the arm has maximum range of movement. Acting as a flexible, crane-like strut, it allows the scapula to move freely on the thoracic wall.
Relation of Brachial Plexus with the ClavicleCovering thecervicoaxillary canal, it protects the neurovascular bundle that supplies the upper limb.
Transmits physical impacts from the upper limb to theaxial skeleton.
A vertical line drawn from the mid-clavicle called themid-clavicular line is used as a reference in describing cardiac apex beat during medical examination. It is also useful for evaluating an enlarged liver, and for locating thegallbladder which is between the mid-clavicular line and thetranspyloric plane.
Clavicle fractures (colloquially, a broken collarbone) occur as a result of injury or trauma. The most common type of fractures occur when a person falls horizontally on the shoulder or with an outstretched hand. A direct hit to the collarbone will also cause a break. In most cases, the direct hit occurs from the lateral side towards the medial side of the bone. The most common site of fracture is the junction between the two curvatures of the bone, which is the weakest point.[11] This results in the sternocleidomastoid muscle lifting the medial aspect superiorly, which can result in perforation of the overlying skin.
The clavicle first appears as part of the skeleton in primitivebony fish, where it is associated with thepectoral fin; they also have a bone called thecleithrum. In such fish, the paired clavicles run behind and below the gills on each side, and are joined by a solidsymphysis on the fish's underside. They are, however, absent incartilaginous fish and in the vast majority of living bony fish, including all of theteleosts.[12]
The earliesttetrapods retained this arrangement, with the addition of a diamond-shapedinterclavicle between the base of the clavicles, although this is not found in livingamphibians. The cleithrum disappeared early in the evolution ofreptiles, and is not found in any livingamniotes, but the interclavicle is present in most modern reptiles, and also inmonotremes. In modern forms, however, there are a number of variations from the primitive pattern. For example,crocodilians andsalamanders lack clavicles altogether (although crocodilians do retain the interclavicle), while inturtles, they form part of the armouredplastron.[12]
The interclavicle is absent inmarsupials andplacental mammals. In many mammals, the clavicles are also reduced, or even absent, to allow the scapula greater freedom of motion, which may be useful in fast-running animals.[12]
Though a number of fossilhominin (humans and chimpanzees) clavicles have been found, most of these are mere segments offering limited information on the form and function of the pectoral girdle. One exception is the clavicle ofAL 333x6/9 attributed toAustralopithecus afarensis which has a well-preserved sternal end. One interpretation of this specimen, based on the orientation of its lateral end and the position of the deltoid attachment area, suggests that this clavicle is distinct from those found in extantapes (including humans), and thus that the shape of the human shoulder dates back to less than3 to 4 million years ago. However, analyses of the clavicle in extant primates suggest that the low position of the scapula in humans is reflected mostly in the curvature of the medial portion of the clavicle rather than the lateral portion. This part of the bone is similar inA. afarensis and it is thus possible that this species had a high shoulder position similar to that inmodern humans.[13]
Indinosaurs, the main bones of thepectoral girdle were thescapula (shoulder blade) and thecoracoid, both of which directly articulated with the clavicle. The clavicle was present insaurischian dinosaurs but largely absent inornithischian dinosaurs. The place on the scapula where it articulated with thehumerus (upper bone of the forelimb) is the called theglenoid. The clavicles fused in sometheropod dinosaurs to form afurcula, which is the equivalent to a wishbone.[14]
In birds, the clavicles and interclavicle have fused to form a single Y-shaped bone, thefurcula or "wishbone" which evolved from the clavicles found in coelurosaurian theropods.[citation needed]
^Shane Tubbs, R.; Loukas, Marios; Slappey, John B.; McEvoy, William C.; Linganna, Sanjay; Shoja, Mohammadali M.; Jerry Oakes, W. (9 July 2007). "Surgical and clinical anatomy of the interclavicular ligament".Surgical and Radiologic Anatomy.29 (5):357–360.doi:10.1007/s00276-007-0219-z.PMID17563831.
^Standring, Susan (2016).Gray's anatomy: the anatomical basis of clinical practice .Digital version (41st ed.). Philadelphia, Pa.: Elsevier. p. 892.ISBN9780702052309.
^Kaur, H; Harjeet Sahni, D (January 2002). "Length and curves of the clavicle in Northwest Indians".Journal of Anatomical Society of India.51 (2):199–209.
^A. Bernat, T. Huysmans, F. Van Glabbeek, J. Sijbers, J. Gielen, and A. Van Tongel (2014). "The anatomy of the clavicle: A Three-dimensional Cadaveric Study".Clinical Anatomy.27 (5):712–723.doi:10.1002/ca.22288.PMID24142486.S2CID23982787.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^abcRomer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 184–186.ISBN978-0-03-910284-5.
^Larson, Susan G. (2009). "Evolution of the Hominin Shoulder: EarlyHomo". In Grine, Frederick E.; Fleagle, John G.; Leakey, Richard E. (eds.).The First Humans – Origin and Early Evolution of the Genus Homo. Vertebrate Paleobiology and Paleoanthropology. Springer. p. 66.doi:10.1007/978-1-4020-9980-9.ISBN978-1-4020-9979-3.
^Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300.ISBN1-4051-3413-5.
