Clavicle

Collarbone and collar bone redirect here. The eye abnormality is correctly spelt coloboma.

In human anatomy, the clavicle or collar bone is a bone that makes up part of the shoulder girdle (pectoral girdle). 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. (This movement is palpable with the opposite hand).

Overview

It is a doubly-curved long bone (the only horizontal long bone in the body) that connects the arm (upper limb) to the body (trunk), located directly above the first rib. 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 scapula (shoulder blade) at the acromioclavicular joint. It is shorter, thinner, less curved, and smoother in women than in men. It has a rounded medial end and a flattened lateral end.

Functions

The clavicle serves several functions:

It serves as a rigid support from which the scapula and free limb are suspended. This arrangement keeps the upper limb away from the thorax so that the arm has maximum range of movement.
Covers the cervicoaxillary canal (passageway between the neck and arm), through which several important structures pass.
Transmits impacts from the upper limb to the axial skeleton.

Even though it is classified as a long bone, the clavicle has no medullary (bone marrow) cavity like other long bones. It is made up of spongy (cancellous) bone with a shell of compact bone. The clavicle bone is the only bone that does not have marrow.

Attachments

Muscles and ligaments that attach to the clavicle include:

Superior surface:

Deltoid muscle at the deltoid tubercle, anteriorly on the lateral third.
Trapezius muscle posteriorly on the lateral third.

Inferior surface:

Subclavius muscle at the subclavian groove
Conoid ligament (the medial part of the coracoclavicular ligament) at the conoid tubercle
Trapezoid ligament (the lateral part of the coracoclavicular ligament) at the trapezoid line

Anterior border:

Pectoralis major muscle on the medial third (rounded border)
Deltoid muscle on the lateral third of border in the deltoid tubercle

Posterior border:

Sternocleidomastoid muscle superiorly, on the medial third (clavicular head of Sternocleidomastoid)
Sternohyoid inferiorly, on the medial third
Trapezius on the lateral third

Development

The clavicle is the first bone to begin the process of hardening (ossification) during development of the embryo, during the 5th and 6th weeks of gestation. However, it is the last of the long bones to finish ossification, at about 21 years of age. It forms by intramembranous ossification.

Common clavicle injuries

Note about anatomical position

Note: this article uses some professional terms to explain certain anatomical details. These words apply only when the body is in anatomical position, i.e., standing with palms of the hands facing forward. These terms are:

superior - above
inferior - below
abduction - the movement of the limb away from the body
medial - toward the midline
lateral - away from the midline

Please visit the anatomical position page for more detailed information.

External links

References

Chung, Kyung. Board Review Series: Gross Anatomy, 4th edition.
Moore, Keith L. and Arthur F. Dalley. Clinically Oriented Anatomy, 4th edition.
Stedman's Medical Dictionary, 27th edition.
Mosby's Medical, Nursing, and Allied Health Dictionary, 5th ed.

Skeletal system | Upper limb anatomy

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