Clavicle-3d-Anatomy

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Clavicle-3d-Anatomy

Anatomy of Clavicle

This S-shaped bone looking like a tendril is called collarbone or the Clavicle, the name coming from its Latin origin Clavicula a Latin word for TENDRIL.

Clavicle Image- Collar Bone, Clavicula, Tendril

However some books still claim that the word is derived from the Latin words Clavis (key) and the combination of its root with the diminutive –cle would suggest that the clavicle is a small key, but this turns out to be incorrect, especially since this bone has no resemblance of a key. The only explanation that makes some sense in this context is if you consider the fact that the clavicle is more like a metaphorical key that locks the shoulder girdle to the trunk.

Comparision between clavicle and a traditional key - No specific resemblance

This bone is very peculiar in the fact that it is the only long bone that lies horizontally and there is no other long bone in the body which lies as such.

This is also the only bone in the body which is subcutaneous throughout its length. One can easily inspect and palpate the entire length of the clavicle lying just below the skin.

However, the most important peculiarity of the bone is the fact that this bone has two, very very different primary centers of ossification, giving us a hint of its complex developmental origin. If you look at the structure of the clavicle, the medial end is rounded and flared like a trumpet while the lateral end is flattened superoinferiorly.

Ossification centers of the clavicle

This variation in the shape can be traced back to its development. See the medial part of the clavicle develops from preformed cartilage like other bones and develops endochondrally thus giving it the tubular appearance and a medial epiphysis. The lateral part of the clavicle develops intra-membranously like the cranial vault bones, which explains the flatter appearance of the acromial end and absence of a distal epiphysis.

The shaft is ossified in condensed mesenchyme from two primary centres, medial and lateral. These centers appear between the fifth and sixth weeks of intrauterine life and fuse about the fourth–fifth day.

Sit of appearance Time of appearance Time of fusion
Two primary centers in the shaft 5-6 weaks of intrauterine life 45th day of intrauterine life
Secondary center at sternal end 19-20 years 25th year
Secondary center at acromial end 20th year Fuses immediately

Structure

The medial end of the clavicle is stout, round and has an articular surface on its medial surface. This is where it is attached to the manubrium of the sternum. There is also a small facet lipping here which is for the attachment of the first costal cartilage.

Medial End of the clavicle -Sternal End - Facet Lipping for the first costal cartilage

The lateral end of the acromial end of the clavicle is flatter and wider than the sternal end. It has the acromial facet on its surface which articulates with the acromial process of the scapula. Lateral End of the clavicle - Lateral End - Facet for acromial cartilage

On the posteroinferior surface of the clavicle is this subclavian groove, which forms the roof over the great vessels of the neck. Though this arrangement looks simple, it is quite effective. See whenever there is a fracture of the clavicle, there is always a risk of injury to the blood vessels of the neck from the jagged fractured edges. However, the subclavius muscle is attached to the subclavian groove and this muscle prevents the motion in the free edges of the fractured bone and protects the blood vessels from injury.

On the lateral end of the clavicle, posteriorly you can find the conoid tubercle. The conoid ligament attaches with the clavicle here and joins with scapula at the coracoid process. This ligament helps to reinforce the joint between the scapula and the clavicle. Conoid tubercle - Conoid Process - Trapezoid Line From the conoid tubercle, an oblique ridge leads laterally, this ridge is called the trapezoid line. This is where the trapezoid ligament is attached, whose function is similar to that of the conoid ligament.

On the posteroinferior edge, you can find a small hole exiting the bone medially. This is the nutrient foramen of the clavicle and transmits a branch of the suprascapular artery.

The superior surface of the clavicle is smoother than the inferior surface, despite the fact that three major muscles- Trapezius, Deltoideus and Pectoralis major are attached here.

This is the rugosity for trapezius muscle. This is where the trapezius muscle is attached on the posterolateral portion of the superior surface of the clavicle.

This rugosity on the anterolateral margin of the superior surface of the clavicle is the rugosity for the deltoideus muscle. This is where deltoid originates.

The Pectoralis major is attached to the anteromedial portion on this rugosity.

This sulcus is the costoclavicular sulcus. This is a variable trait and its presence would be an indicator of habitual activity. Activities involving repetitive rotary or back and forth motions of the shoulder would make this sulcus into a ridge. When present, the costoclavicular sulcus is an irregularly roughened surface and it anchors the costoclavicular ligament, which strengthens the sternoclavicular joint.

The female clavicle is typically shorter, thinner, less curved and smoother than the male. In forensic investigations, mid-shaft circumference is considered to be the most reliable single indicator of sex of the person from the bones.

Attachments

The lateral end of the clavicle gives attachment to the joint capsule for the acromioclavicular joint. This joint provides the ability to raise the arm above the head by functioning as a pivot point, acting like a strut to help with movement of the scapula resulting in a greater degree of arm rotation.

The medial end gives attachment to the fibrous capsule of the sternoclavicular joint all around and it also gives articular disc posterosuperiorly and interclavicular ligament superiorly.

The lateral one-third of the shaft gives origin to the deltoid in the anterior border and the posterior border provides the insertion for trapezius. The conoid tubercle and the trapezoid ridge give attachments to the conoid and the trapezoid parts of the coracoclavicular joint.

The medial two-thirds of the shaft on the anterior surface gives origin to the pectoralis major. The sternocleidomastoid muscle originates from the half of the rough superior surface. This oval impression on the inferior surface on the medial end gives attachment to the costoclavicular ligament. Subclavian groove seen here is where the subclavius muscle inserts. The margins of this groove give attachment to the clavipectoral fascia. The posterior surface close to the medial end gives origin to the sternohyoid muscle.

Cut Section

Laterally the internal structure of the clavicle is trabecular while there is a distinct medullary cavity in the medial two thirds. The cortical bone is thickest at the transition zone between the antecurve and the retrocurve.

Siding

Medial end is round and the lateral end is flat

From medial to lateral, the bone first bows anteriorly and then it curves posteriorly at the midshaft and then again it sweeps anteriorly till it reaches the lateral flat end of the acromion.

Most of the irregularities are present on the inferior surface than the superior surface of the clavicle.

The facet for first costal cartilage and the costoclavicular impression or the costal tuberosity is on the inferior edge of the medial clavicle.

Clinical Anatomy

The clavicles could also be congenitally absent, or sometimes poorly developed in a disease termed cleidocranial dysostosis. As observed in stars of hereditary and stranger things, this disease is caused due to a mutation in chromosome 6 and is inherited in autosomal dominant fashion. There is shoulder droop and the shoulders can be approximated anteriorly in front of the chest, along with teeth disorders and bone abnormalities.

The clavicle is usually fractured medial to the conoid tubercle because the middle third of the bone is not reinforced with ligaments or muscles. Clavicle fractures are typically treated by putting the arm in a sling for one or two weeks along with NSAIDS.

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