In
humanHumans are the only living species in the Homo genus...
anatomyAnatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
, the
clavicle or
collar bone is a
long boneThe long bones are those that are longer than they are wide. They are one of five types of bones: long, short, flat, irregular and sesamoid. Long bones, especially the femur and tibia, are subjected to most of the load during daily activities and they are crucial for skeletal mobility. They grow...
of short length that serves as a strut between the
scapulaIn anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
and the sternum. It is the only long bone in body that lies horizontally. It makes up part of the
shoulderThe human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...
and the
pectoral girdle and is palpable in all people, and, in people who have less fat in this region, the location of the bone is clearly visible as it creates a bulge in the skin.
It receives its name from the ("little key") because the bone rotates along its axis like a key when the shoulder is
abductedAbduction, in functional anatomy, is a movement which draws a limb away from the median plane of the body. It is thus opposed to adduction.-Upper limb:* of arm at shoulder ** Supraspinatus** Deltoid* of hand at wrist...
, and it roughly the same shape as Roman door lock keys.
Human anatomy
 |
| Right clavicle — from below, and from above. |
|
| Left clavicle — from above, and from below. |
The clavicle is a doubly curved short bone that connects the arm (
upper limbThe upper limb or upper extremity is the region in an animal extending from the deltoid region to the hand, including the arm, axilla and shoulder.-Definition:...
) to the body (
trunkTrunk or torso is an anatomical term for the central part of the many animal bodies from which extend the neck and limbs. The trunk includes the thorax and abdomen.-Major organs:...
), located directly above the first rib. It acts as a strut to keep the scapula in position so the arm can hang freely. Medially, it articulates with the manubrium of the sternum (breast-bone) at the sternoclavicular joint. At its lateral end it articulates with the acromion of the
scapulaIn anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
(shoulder blade) at the
acromioclavicular jointThe acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion and the clavicle. -Function:...
. It has a rounded medial end and a flattened lateral end.
From the roughly pyramidal sternal end, each clavicle curves laterally and anteriorly for roughly half its length. It then forms a smooth posterior curve to articulate with a process of the scapula (acromion). The flat, acromial end of the clavicle is broader than the sternal end. The acromial end has a rough inferior surface that bears prominent line,
Trapezoid lineFrom the conoid tubercule an oblique ridge, the trapezoid line , runs forward and lateralward, and affords attachment to the trapezoid ligament....
and a small rounded projection,
Conoid tubercleAt the posterior inferior side of the clavicle, near the point where the prismatic joins with the flattened portion, is a rough eminence, the conoid tubercle ; this, in the natural position of the bone, surmounts the coracoid process of the scapula, and gives attachment to the conoid ligament....
. 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.
Medial End
The
medialStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
end is quadrangular and articulates with clavicular notch of menubrium sterni to form sternoclavicular joint. Articular surface extends to inferior aspect for attachment with first costal cartilage.
It gives attachments to
1. Fibrous capsule of sternoclavicular joint
all around
2. Articular disc
superoposteriorly
3. Interclavicular ligament
superiorly
Lateral End
The lateral end is flat from above downward. It bears a facet for attachment to acromion process of scapula forming acromioclavicular joint. The area surrounding the joint gives attachment to joint capsule.
Shaft
The shaft is divided into medial 2/3 and lateral 1/3. Medial 2/3 is thicker than lateral 1/3.
Medial 2/3 of shaft
Medial 2/3 of shaft has 4 surfaces and no borders.
Anterior surface is convex forward and gives origin to pectoralis major.
Posterior surface is smooth and gives origin to
sternohyoid muscleThe sternohyoid muscle is a thin, narrow muscle attaching the hyoid bone to the sternum, one of the paired strap muscles of the infrahyoid muscles serving to depress the hyoid bone...
at its medial end.
Superior surface is rough at its medial part and gives origin to
sternocleidomastoid muscleIn human anatomy, the sternocleidomastoid muscle , also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the anterior portion of the neck...
.
Inferior surface has an oval impression at its medial end for
costoclavicular ligamentThe costoclavicular ligament , is the anatomical name of a ligament that is short, flat, strong, and rhomboid in form....
. At the lateral side of inferior surface, there is a
subclavian grooveOn the medial part of the clavicle is a broad rough surface, the costal tuberosity , rather more than 2 cm. in length, for the attachment of the costoclavicular ligament. The rest of this surface is occupied by a groove, which gives attachment to the Subclavius; the coracoclavicular fascia, which...
for insertion of
subclavius muscleThe Subclavius is a small triangular muscle, placed between the clavicle and the first rib.Along with the pectoralis major and pectoralis minor muscles, the subclavius muscle makes up the anterior wall of the axilla.-Origin and insertion:...
. At the lateral side of subclavian groove, nutrient foramen lies.
Lateral 1/3 of shaft
It has 2 borders and 2 surfaces.
Anterior border is concave forward and gives origin to
deltoid muscleIn human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
.
Posterior border is convex backward and gives attachment to
trapezius muscleIn human anatomy, the trapezius is a large superficial muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula...
.
Superior surface is subcutaneous.
Inferior surface has a ridge called
trapezoid lineFrom the conoid tubercule an oblique ridge, the trapezoid line , runs forward and lateralward, and affords attachment to the trapezoid ligament....
and a tubercle, the
conoid tubercleAt the posterior inferior side of the clavicle, near the point where the prismatic joins with the flattened portion, is a rough eminence, the conoid tubercle ; this, in the natural position of the bone, surmounts the coracoid process of the scapula, and gives attachment to the conoid ligament....
for attachment with trapezoid and conoid part of
coracoclavicular ligamentThe Coracoclavicular Ligament serves to connect the clavicle with the coracoid process of the scapula.It does not properly belong the acromioclavicular joint articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion...
that serves to connect the clavicle with the coracoid process of the scapula.
Attachments
Muscles and ligaments that attach to the clavicle include:
! Attachment on clavicle !! Muscle/Ligament !! Other attachment
|-
| Superior surface and anterior border >
Deltoid muscleIn human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
|
|
>-
| Superior surface
Trapezius muscle In human anatomy, the trapezius is a large superficial muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula...
|
|
>-
| Inferior surface
Subclavius muscle The Subclavius is a small triangular muscle, placed between the clavicle and the first rib.Along with the pectoralis major and pectoralis minor muscles, the subclavius muscle makes up the anterior wall of the axilla.-Origin and insertion:...
|
subclavian groove On the medial part of the clavicle is a broad rough surface, the costal tuberosity , rather more than 2 cm. in length, for the attachment of the costoclavicular ligament. The rest of this surface is occupied by a groove, which gives attachment to the Subclavius; the coracoclavicular fascia, which...
>-
| Inferior surface |
Conoid ligament The Conoid Ligament, the posterior and medial fasciculus, is a dense band of fibers, conical in form, with its base directed upward.It is attached by its apex to a rough impression at the base of the coracoid process, medial to the trapezoid ligament; above, by its expanded base, to the coracoid...
(the medial part of the coracoclavicular ligamentThe Coracoclavicular Ligament serves to connect the clavicle with the coracoid process of the scapula.It does not properly belong the acromioclavicular joint articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion...
) |
conoid tubercle At the posterior inferior side of the clavicle, near the point where the prismatic joins with the flattened portion, is a rough eminence, the conoid tubercle ; this, in the natural position of the bone, surmounts the coracoid process of the scapula, and gives attachment to the conoid ligament....
>-
| Inferior surface |
Trapezoid ligament The trapezoid ligament, the anterior and lateral fasciculus, is broad, thin, and quadrilateral: it is placed obliquely between the coracoid process and the clavicle....
(the lateral part of the coracoclavicular ligamentThe Coracoclavicular Ligament serves to connect the clavicle with the coracoid process of the scapula.It does not properly belong the acromioclavicular joint articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion...
) |
trapezoid line From the conoid tubercule an oblique ridge, the trapezoid line , runs forward and lateralward, and affords attachment to the trapezoid ligament....
>-
| Anterior border |
Pectoralis major muscle The pectoralis major is a thick, fan-shaped muscle, situated at the chest of the body. It makes up the bulk of the chest muscles in the male and lies under the breast in the female...
|
|
>-
| Posterior border
Sternocleidomastoid muscleIn human anatomy, the sternocleidomastoid muscle , also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the anterior portion of the neck...
(clavicular head) |
|
>-
| Posterior border
Sternohyoid muscle The sternohyoid muscle is a thin, narrow muscle attaching the hyoid bone to the sternum, one of the paired strap muscles of the infrahyoid muscles serving to depress the hyoid bone...
|
|
>-
| Posterior border
Trapezius muscle In human anatomy, the trapezius is a large superficial muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula...
|
lateral third |
The
levator claviculae muscleIn human anatomy, the levator claviculae is a very rare accessory and vestigial skeletal muscle in the posterior triangle of the neck. It originates on the transverse processes of the upper cervical vertebrae and is inserted in the lateral half of the clavicle...
, 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.
Functions
The clavicle serves several functions:
- It serves as a rigid support from which the scapula and free limb (arm) are suspended; an arrangement that keeps the upper limb away from the thorax so that the arm has maximum range of movement. Acting as flexible, crane-like strut, it allows the scapula to move freely on the thoracic wall.
- Covering the cervicoaxillary canal, it protects the neurovascular bundle that supply the upper limb.
- Transmits physical impacts from the upper limb to the axial skeleton
The axial skeleton consists of the 80 bones along the central axis of the human body. It is composed of six parts; the human skull, the ossicles of the middle ear, the hyoid bone of the throat, the rib cage, sternum and the vertebral column...
.
Development
The clavicle is the first bone to begin the process of
ossificationOssification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
(laying down of minerals onto a preformed matrix) during development of the embryo, during the 5th and 6th weeks of gestation. However, it is one of the last bones to finish ossification, at about 21–25 years of age. It's lateral end is formed by
intramembranous ossificationIntramembranous ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike endochondral ossification, which is the other process by which bone tissue is created, cartilage is not present during intramembranous...
while medially it is formed by endochondral ossification. It consists of a mass of
cancellous bone surrounded by a compact bone shell. The cancellous bone forms via two ossification centres, one medial and one lateral, which fuse later on. The compact forms as the layer of
fasciaA fascia is a layer of fibrous tissue that permeates the human body. A fascia is a connective tissue that surrounds muscles, groups of muscles, blood vessels, and nerves, binding those structures together in much the same manner as plastic wrap can be used to hold the contents of sandwiches...
covering the bone stimulates the ossification of adjacent tissue. The resulting compact bone is known as a periosteal collar.
Even though it is classified as a
long boneThe long bones are those that are longer than they are wide. They are one of five types of bones: long, short, flat, irregular and sesamoid. Long bones, especially the femur and tibia, are subjected to most of the load during daily activities and they are crucial for skeletal mobility. They grow...
, the clavicle has no medullary (bone marrow) cavity like other long bones ,though this is not always true . It is made up of spongy (trabecular) bone with a shell of compact bone. It is a
dermal boneA dermal bone - bony structures derived from intramembranous ossification that form components of the vertebrate skeleton including the skull, jaws, gills, fins and exoskeleton. In contrast to endochondral bone, dermal bone does not form from cartilage first and then calcify...
derived from elements originally attached to the skull.
Variations
The shape of the clavicle varies more than most other long bones. It is occasionally pierced by a branch of the supraclavicular nerve. In manual workers it is thicker and more curved and the sites of muscular attachments are more pronounced. The right clavicle is usually stronger and shorter than the left clavicle.
In females the clavicle is thinner , smoother and lighter than that of males. Clavicle is a reliable criteria for sex determination
Common clavicle injuries
- Acromioclavicular dislocation ("AC Separation")
- Clavicle fracture
A clavicle fracture is a bone fracture in the clavicle, or collarbone. It is often caused by a fall onto an outstretched upper extremity, a fall onto a shoulder, or a direct blow to the clavicle...
s
- Degeneration of the clavicle
- The collarbones are sometimes partly or completely absent in cleidocranial dysostosis
Cleidocranial dysostosis, also called Cleidocranial dysplasia, is a hereditary congenital disorder due to haploinsufficiency caused by mutations in the CBFA1 gene also called Runx2, located on the short arm of chromosome 6....
- Osteolysis
Osteolysis refers to an active resorption of bone matrix by osteoclasts as part of an ongoing disease process.-Osteolysis in joint replacement:...
- Sternoclavicular dislocations
Evolutionary variation
The clavicle first appears as part of the skeleton in primitive
bony fishOsteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...
, where it is associated with the pectoral fin; they also have a bone called the
cleithrumThe cleithrum is a membrane bone which first appears as part of the skeleton in primitive bony fish, where it runs vertically along the scapula. Its name is derived from Greek κλειθρον = "key ", by analogy with "clavicle" from Latin clavicula = "little key".In modern fishes, the cleithrum is a...
. In such fish, the paired clavicles run behind and below the gills on each side, and are joined by a solid
symphysisA symphysis is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint.1.A symphysis is an amphiarthrosis, a slightly movable joint.2.A growing together of parts or structures...
on the fish's underside. They are, however, absent in cartilagenous fish and in the vast majority of living bony fish, including all of the teleosts.
The earliest
tetrapodTetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s retained this arrangement, with the addition of a diamond-shaped
interclavicle between the base of the clavicles, although this is not found in living
amphibianAmphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s. The cleithrum disappeared early in the evolution of
reptileReptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, and is not found in any living
amnioteThe amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...
s, but the interclavicle is present in most modern reptiles, and also in
monotremeMonotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...
s. In modern forms, however, there are a number of variations from the primitive pattern. For example, crocodilians and
salamanderSalamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s lack clavicles altogether (although crocodilians do retain the interclavicle), while in
turtleTurtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, they form part of the armoured plastron.
In birds, the clavicles and interclavicle have fused to form a single Y-shaped bone, the
furculaThe ' is a forked bone found in birds, formed by the fusion of the two clavicles. In birds, its function is the strengthening of the thoracic skeleton to withstand the rigors of flight....
or "wishbone".
The interclavicle is absent in
marsupialMarsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s and placental 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.
Though a number of fossil hominin (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 clavice of
AL 333x6/9AL 333, commonly referred to as the "First Family", is a collection of prehistoric hominid teeth and bones. Discovered in 1975 by Donald Johanson's team in Hadar, Ethiopia, the “First Family” is estimated to be about 3.2 million years old and consists of the remains of at least thirteen...
attributed to
Australopithecus afarensisAustralopithecus afarensis is an extinct hominid that lived between 3.9 and 2.9 million years ago. A. afarensis was slenderly built, like the younger Australopithecus africanus. It is thought that A...
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 extant
apeApes are Old World anthropoid mammals, more specifically a clade of tailless catarrhine primates, belonging to the biological superfamily Hominoidea. The apes are native to Africa and South-east Asia, although in relatively recent times humans have spread all over the world...
s (including humans), and thus that the shape of the human shoulder dates back to less than . 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 in
A. afarensis and it is thus possible that this species had a high shoulder position similar to that in
modern humansThe term anatomically modern humans in paleoanthropology refers to early individuals of Homo sapiens with an appearance consistent with the range of phenotypes in modern humans....
.
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