Clavicle

The clavicle or collarbone is a long bone that serves as a strut between the shoulder blade and the sternum or breastbone. There are two clavicles, one on the left and one on the right. The clavicle is the only long bone in the body that lies horizontally. Together with the shoulder blade it makes up the shoulder girdle. It is a touchable bone 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 Latin: clavicula ("little key") because the bone rotates along its axis like a key when the shoulder is abducted. The clavicle is the most commonly fractured bone. It can easily be fractured due to impacts to the shoulder from the force of falling on outstretched arms or by a direct hit.[1]

Clavicle (collarbone)
Clavicle - anterior view
Collarbone (shown in red)
ClavicleSen
Human collarbone
Details
Identifiers
LatinClavicula
MeSHD002968
TAA02.4.02.001
FMA13321
Anatomical terms of bone

Structure

The collarbone, a large doubly curved long bone that connects the arm to the trunk of the body. Located directly above the first rib it acts as a strut to keep the scapula in place so that the arm can hang freely. Medially, it articulates with the manubrium of the sternum (breastbone) at the sternoclavicular joint. At its lateral end it articulates with the acromion, a process of the scapula (shoulder blade) at the acromioclavicular joint. It has a rounded medial end and a flattened lateral end.

Clavicula inf

Clavicula sup
Right clavicle—from below, and from above
Gray200

Gray201
Left clavicle—from above, and from below

From the roughly pyramidal sternal end, each collarbone curves laterally and anteriorly for roughly half its length. It then forms an even larger posterior curve to articulate with the acromion of the scapula. The flat acromial end of the collarbone is broader than the sternal end. The acromial end has a rough inferior surface that bears a ridge, the trapezoid line, and a slight rounded projection, the conoid tubercle (above the coracoid 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.

Medial end

The medial end is quadrangular and articulates with the clavicular notch of the manubrium of the sternum to form the sternoclavicular joint. The articular surface extends to the inferior aspect for attachment with the first costal cartilage.

It gives attachments to:

  • fibrous capsule joint, all around
  • articular disc, superoposteriorly
  • interclavicular ligament, superiorly

Lateral end

The lateral end is flat from above downward. It bears a facet for attachment to the acromion process of the scapula, forming the acromioclavicular joint. The area surrounding the joint gives an attachment to the joint capsule. The anterior border is concave forward and posterior border is convex backward.

Shaft

The shaft is divided into the medial two-thirds and the lateral one third. The medial part is thicker than the lateral.

Clavicle 3d Model
Clavicle 3d Model

Medial two-thirds of the shaft

The medial two-thirds of the shaft has four surfaces and no borders.

  1. The anterior surface is convex forward and gives origin to the pectoralis major.
  2. The posterior surface is smooth and gives origin to the sternohyoid muscle at its medial end.
  3. The superior surface is rough at its medial part and gives origin to the sternocleidomastoid muscle.
  4. The inferior surface has an oval impression inferior to its medial end for the costoclavicular ligament and is called costal tuberosity. At the lateral side of the inferior surface, there is a subclavian groove for insertion of the subclavius muscle. At the lateral side of the subclavian groove, the nutrient foramen lies. The medial part is quadrangular in shape where it makes a joint with the manubrium of the sternum at the sternoclavicular joint. The margins of the subclavian groove give attachment to the clavipectoral fascia.

Lateral third of the shaft

The lateral third of the shaft has two borders and two surfaces.

Development

The collarbone is the first bone to begin the process of ossification (laying down of minerals onto a preformed matrix) during development of the embryo, during the fifth and sixth weeks of gestation. However, it is one of the last bones to finish ossification at about 21–25 years of age. Its lateral end is formed by intramembranous ossification 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 fascia 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 bone, the collarbone has no medullary (bone marrow) cavity like other long bones, though this is not always true. It is made up of spongy cancellous bone with a shell of compact bone.[2] It is a dermal bone derived from elements originally attached to the skull.

Variation

The shape of the clavicle varies more than most other long bones. It is occasionally pierced by a branch of the supraclavicular nerve. In males the clavicle is generally longer and more massive 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.[3]

The left clavicle is usually longer and not as strong as the right clavicle.[2] [4]

The collarbones are sometimes partly or completely absent in cleidocranial dysostosis.

The levator 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.

Functions

The collarbone serves several functions:[2]

  • It serves as a rigid support from which the scapula and free limb 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.
  • Covering the cervicoaxillary canal, it protects the neurovascular bundle that supplies the upper limb.
  • Transmits physical impacts from the upper limb to the axial skeleton.

Muscle

Muscles and ligaments that attach to the collarbone include:

Attachment on collarbone Muscle/Ligament Other attachment
Superior surface and anterior border Deltoid muscle deltoid tubercle, anteriorly on the lateral third
Superior surface Trapezius muscle posteriorly on the lateral third
Inferior surface Subclavius muscle subclavian groove
Inferior surface Conoid ligament (the medial part of the coracoclavicular ligament) conoid tubercle
Inferior surface Trapezoid ligament (the lateral part of the coracoclavicular ligament) trapezoid line
Anterior border Pectoralis major muscle medial third (rounded border)
Posterior border Sternocleidomastoid muscle (clavicular head) superiorly, on the medial third
Posterior border Sternohyoid muscle inferiorly, on the medial third
Posterior border Trapezius muscle lateral third

Clinical significance

A vertical line drawn from the mid-clavicle called the mid-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 the gallbladder which is between the mid-clavicular line and the transpyloric plane.

Collarbone fracture

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. Fractures of the clavicle typically occur at the angle, where the greatest change in direction of the bone occurs. This results in the sternocleidomastoid muscle lifting the medial aspect superiorly, which can result in perforation of the overlying skin.

Other animals

The clavicle first appears as part of the skeleton in primitive bony fish, where it is associated with the pectoral fin; they also have a bone called the cleithrum. In such fish, the paired clavicles run behind and below the gills on each side, and are joined by a solid symphysis on the fish's underside. They are, however, absent in cartilaginous fish and in the vast majority of living bony fish, including all of the teleosts.[5]

The earliest tetrapods retained this arrangement, with the addition of a diamond-shaped interclavicle between the base of the clavicles, although this is not found in living amphibians. The cleithrum disappeared early in the evolution of reptiles, and is not found in any living amniotes, but the interclavicle is present in most modern reptiles, and also in monotremes. In modern forms, however, there are a number of variations from the primitive pattern. For example, crocodilians and salamanders lack clavicles altogether (although crocodilians do retain the interclavicle), while in turtles, they form part of the armoured plastron.[5]

The interclavicle is absent in marsupials 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.[5]

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 clavicle of AL 333x6/9 attributed to Australopithecus 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 extant apes (including humans), and thus that the shape of the human shoulder dates back to less than 3 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 in A. afarensis and it is thus possible that this species had a high shoulder position similar to that in modern humans.[6]

In dinosaurs

In dinosaurs the main bones of the pectoral girdle were the scapula (shoulder blade) and the coracoid, both of which directly articulated with the clavicle. The clavicle was present in saurischian dinosaurs but largely absent in ornithischian dinosaurs. The place on the scapula where it articulated with the humerus (upper bone of the forelimb) is the called the glenoid. The clavicles fused in some theropod dinosaurs to form a furcula, which is the equivalent to a wishbone.[7]

In birds, the clavicles and interclavicle have fused to form a single Y-shaped bone, the furcula or "wishbone" which evolved from the clavicles found in coelurosaurian theropods.

Additional images

Clavicle - animation2

Position of collarbone (shown in red). Animation.

Left clavicle - close-up - animation

Shape of collarbone (left). Animation.

Human clavicle.stl

3D image

Pectoral girdle front diagram

Pectoral girdle—front

Shoulder joint

Diagram of the human shoulder joint, front view

Shoulder joint back-en

Diagram of the human shoulder joint, back view

Gray386

Muscles of the neck. Anterior view.

Clavicle 4

See also

References

  1. ^ "Busy Bones". 2011-05-13.
  2. ^ a b c Moore, Keith L.; Dalley, Arthur F. (1999). Clinically Oriented Anatomy (4th ed.). Lippincott Williams & Wilkins. ISBN 978-0-683-06141-3.
  3. ^ medind.nic.in
  4. ^ 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. PMID 24142486.CS1 maint: Multiple names: authors list (link)
  5. ^ a b c Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 184–186. ISBN 978-0-03-910284-5.
  6. ^ Larson, Susan G. (2009). "Evolution of the Hominin Shoulder: Early Homo". In Grine, Frederick E.; Fleagle, John G.; Leakey, Richard E. 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. ISBN 978-1-4020-9979-3.
  7. ^ Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN 1-4051-3413-5.

External links

Clavicle - BlueLink Anatomy - University of Michigan Medical School

Acromioclavicular joint

The acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle. It is a plane synovial joint.

Anterior sternoclavicular ligament

The anterior sternoclavicular ligament is a broad band of fibers, covering the anterior (front) surface of the joint between the sternum and clavicle (sternoclavicular articulation).

It is attached above to the upper and front part of the sternal end of the clavicle, and, passing obliquely downward and medialward, is attached below to the front of the upper part of the manubrium on the sternum.

This ligament is covered by the sternal portion of the sternocleidomastoideus and the integument; behind, it is in relation with the capsule, the articular disk, and the two synovial membranes.

Clavicle fracture

A clavicle fracture, also known as a broken collarbone, is a bone fracture of the clavicle. Symptoms typically include pain at the site of the break and a decreased ability to move the affected arm. Complications can include a collection of air in the pleural space surrounding the lung (pneumothorax), injury to the nerves or blood vessels in the area, and an unpleasant appearance.It is often caused by a fall onto a shoulder, outstretched arm, or direct trauma. The fracture can also occur in a baby during childbirth. The middle section of the clavicle is most often involved. Diagnosis is typically based on symptoms and confirmed with X-rays.Clavicle fractures are typically treated by putting the arm in a sling for one or two weeks. Pain medication such as paracetamol (acetaminophen) may be useful. It can take up to five months for the strength of the bone to return to normal. Reasons for surgical repair include an open fracture, involvement of the nerves or blood vessels, or shortening of the clavicle by more than 1.5 cm in a young person.Clavicle fractures most commonly occur in people under the age of 25 and those over the age of 70. Among the younger group males are more often affected than females. In adults they make up about 5% of all fractures while in children they represent about 13% of fractures.

Cleithrum

The 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 (lock)", by analogy with "clavicle" from Latin clavicula = "little key".

In modern fishes, the cleithrum is a large bone that extends upwards from the base of the pectoral fin and anchors to the cranium above the gills, forming the posterior edge of the gill chamber. The bone has scientific use as a means to determine the age of fishes.

The lobe-finned fishes share this arrangement. In the earliest amphibians however, the cleithrum/clavicle complex came free of the skull roof, allowing for a movable neck. The cleithrum disappeared early in the evolution of reptiles, and in amniotes is very small or absent.

Coracoclavicular ligament

The coracoclavicular ligament serves to connect the clavicle with the coracoid process of the scapula.

It does not properly belong to the acromioclavicular (AC) joint articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion. It consists of two fasciculi, the trapezoid ligament in front, and the conoid ligament behind. There is very little movement at the AC joint.

These ligaments are in relation, in front, with the subclavius and deltoideus; behind, with the trapezius. The coracoclavicular ligament is the strongest stabilizer of the AC joint. This ligament is very important in the transmission of weight of the upper limb to the axial skeleton.

Costal tuberosity of clavicle

On the medial part of the clavicle is a broad rough surface, the costal tuberosity (impression for costoclavicular ligament), rather more than 2 cm. in length, for the attachment of the costoclavicular ligament.

Platysma muscle

The platysma is a superficial muscle that overlaps the sternocleidomastoid.

It is a broad sheet arising from the fascia covering the upper parts of the pectoralis major and deltoid; its fibers cross the clavicle, and proceed obliquely upward and medially along the side of the neck.Fibres at the front of the muscle from the left and right sides intermingle together below and behind the symphysis menti; the junction where the two lateral halves of the mandible are fused at an early period of life. It is not a true symphysis as there is no cartilage between the two sides of the mandible. Fibres at the back of the muscle cross the mandible, some being inserted into the bone below the oblique line, others into the skin and subcutaneous tissue of the lower part of the face. Many of these fibers blend with the muscles about the angle and lower part of the mouth.

Sometimes fibers can be traced to the zygomaticus, or to the margin of the orbicularis oris. Beneath the platysma, the external jugular vein descends from the angle of the mandible to the clavicle.

Separated shoulder

A separated shoulder, also known as acromioclavicular joint injury, is a common injury to the acromioclavicular joint. The AC joint is located at the outer end of the clavicle where it attaches to the acromion of the scapula. Symptoms include pain which may make it difficult to move the shoulder and often a deformity.It is most commonly due to a fall onto the front and upper part of the shoulder when the arm is by the side. They are classified as type I, II, III, IV, V, or VI with the higher the number the more severe the injury. Diagnosis is typically based on physical examination and X-rays. In type I and II injuries there is minimal deformity while in a type III injury the deformity resolves upon lifting the arm upwards. In type IV, V, and VI the deformity does not resolve with lifting the arm.Generally types I and II are treated without surgery, while type III may be treated with or without surgery, and types IV, V, and VI are treated with surgery. For type I and II treatment is usually with a sling and pain medications for a week or two. In type III injuries surgery is generally only done if symptoms remain following treatment without surgery.A separated shoulder is a common injury among those involved in sports, especially contact sports. It makes up about half of shoulder injuries among those who play hockey, football, and rugby. Those affected are typically 20 to 30 years old. Males are more often affected than females. The injury was initially classified in 1967 with the current classification from 1984.

Shoulder

The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The shoulder joint, also known as the glenohumeral joint, is the major joint of the shoulder, but can more broadly include the acromioclavicular joint. In human anatomy, the shoulder joint comprises the part of the body where the humerus attaches to the scapula, and the head sits in the glenoid cavity. The shoulder is the group of structures in the region of the joint.The shoulder joint is the main joint of the shoulder. It is a ball and socket joint that allows the arm to rotate in a circular fashion or to hinge out and up away from the body. The joint capsule is a soft tissue envelope that encircles the glenohumeral joint and attaches to the scapula, humerus, and head of the biceps. It is lined by a thin, smooth synovial membrane. The rotator cuff is a group of four muscles that surround the shoulder joint and contribute to the shoulder's stability. The muscles of the rotator cuff are supraspinatus, subscapularis, infraspinatus, and teres minor. The cuff adheres to the glenohumeral capsule and attaches to the humeral head.

The shoulder must be mobile enough for the wide range actions of the arms and hands, but stable enough to allow for actions such as lifting, pushing, and pulling.

Shoulder 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 the clavicle, scapula, and coracoid. Some mammalian species (such as the dog and the horse) have only the scapula.

The pectoral girdles are to the upper limbs as the pelvic girdle is to the lower limbs; the girdles are the parts of the appendicular skeleton that anchor the appendages to the axial skeleton.

In humans, the only true anatomical joints between the shoulder girdle and the axial skeleton are the sternoclavicular joints on each side. No anatomical joint exists between each scapula and the rib cage; instead the muscular connection or physiological joint between the two permits great mobility of the shoulder girdle compared to the compact pelvic girdle; because the upper limb is not usually involved in weight bearing, its stability has been sacrificed in exchange for greater mobility. In those species having only the scapula, no joint exists between the forelimb and the thorax, the only attachment being muscular.

Sternoclavicular joint

The sternoclavicular joint or sternoclavicular articulation is the joint between the manubrium of the sternum and the clavicle bone. It is structurally classed as a synovial saddle joint and functionally classed as a diarthrosis and multiaxial joint. It is composed of two portions separated by an articular disc of fibrocartilage. The bone areas entering into its formation are the sternal end of the clavicle, the upper and lateral part of the sternum, (the clavicular notch), and the cartilage of the first rib, visible from the outside as the suprasternal notch. The articular surface of the clavicle is much larger than that of the sternum, and is invested with a layer of cartilage, which is considerably thicker than that on the sternum.

The costoclavicular ligament is the main limitation to movement, and therefore the main stabilizer of the joint. A fibrocartilaginous disc present at the joint increases the range of movement. Sternoclavicular dislocation is rare, but may result from direct trauma to the clavicle or indirect forces applied to the shoulder. Posterior dislocations deserve special attention, as they have the potential to be life-threatening because of the risk of damage to vital structures in the mediastinum.

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 accessory nerve.

It is given the name sternocleidomastoid because it originates at the manubrium of the sternum (sterno-) and the clavicle (cleido-), and has an insertion at the mastoid process of the temporal bone of the skull.

Subclavian groove

On the medial part of the clavicle is a broad rough surface, the costal tuberosity (rhomboid impression), 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 splits to enclose the muscle, is attached to the margins of the groove. Not infrequently this groove is subdivided longitudinally by a line which gives attachment to the intermuscular septum of the Subclavius.

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.

Throat

In vertebrate anatomy, the throat is the front part of the neck, positioned in front of the vertebra. It contains the pharynx and larynx. An important section of it is the epiglottis, which is a flap separating the esophagus from the trachea (windpipe) preventing food and drink being inhaled into the lungs. The throat contains various blood vessels, pharyngeal muscles, the nasopharyngeal tonsil, the tonsils, the palatine uvula, the trachea, the esophagus, and the vocal cords. Mammal throats consist of two bones, the hyoid bone and the clavicle. The "throat" is sometimes thought to be synonymous for the isthmus of the fauces.It works with the mouth, ears and nose, as well as a number of other parts of the body. Its pharynx is connected to the mouth, allowing speech to occur, and food and liquid to pass down the throat. It is joined to the nose by the nasopharynx at the top of the throat, and to ear by its Eustachian tube. The throat's trachea carries inhaled air to the bronchi of the lungs. The esophagus carries food through the throat to the stomach. Adenoids and tonsils help prevent infection and are composed of lymph tissue. The larynx contains vocal cords, the epiglottis (preventing food/liquid inhalation), and an area known as the subglottic larynx—the narrowest section of the upper part of the throat. In the larynx, the vocal cords consist of two membranes that act according to the pressure of the air.

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.

It is attached, below, to the upper surface of the coracoid process; above, to the oblique ridge on the under surface of the clavicle.

Its anterior border is free; its posterior border is joined with the conoid ligament, the two forming, by their junction, an angle projecting backward.

Trapezoid line

From the conoid tubercle an oblique ridge, the trapezoid line (or trapezoid ridge, or oblique), runs forward and lateralward, and affords attachment to the trapezoid ligament on inferior surface of clavicle

Weaver–Dunn procedure

This is a generally successful type of surgery involved in the treatment of severe separated shoulders developed by James K. Weaver, M.D., Albuquerque, NM, and Harold K. Dunn, M.D., Salt Lake City, UT in the early 1970s.The procedure is done to essentially replace the coracoclavicular ligaments with the coracoacromial ligament.There is currently no "gold standard" surgery to repair acromioclavicular separations, and many surgeries have been created. However, this is one of the more common fixes.

The original surgery is described as follows.

Resection of the distal 2 cm of distal clavicle

Detaching the acromial end of the coracoacromial ligament, and possibly shortening it.

Attaching the remaining ligament to the remaining clavicle with sutures.Modern variations of the procedure may use additional fixation methods to better stabilize the distal clavicle end as the original construction is rather weak compared to the unharmed shoulder. Even with these modifications, the modern surgeries do not match intact coracoclavicular ligament strength in cadaveric testing. However, such testing does not account for what the living body may perform in the process of healing, in terms of joint remodeling, etc.

Well-Tempered Clavicle

Well-Tempered Clavicle is the 35th book of the Xanth series by Piers Anthony. The title is a pun on the Bach musical work The Well-Tempered Clavier.

The back cover of the book states the following:

"When a walking skeleton named Picka Bones happens upon a trio of melodic pets and a lovely, lovelorn princess, his dull and passionless existence is suddenly filled with danger, excitement, and the temptations of the flesh. For a plague of appalling puns has been unleashed on Xanth, and only Picka's musical gifts have the power to save the enchanted realm from the dire monster who imperils it."

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