Clavicle

Overview
In human anatomy, the clavicle or collar bone is classified as a long 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). In some people, particularly females who may have less fat in this region, the location of the bone is clearly visible as it creates a bulge in the skin.

Overview
The clavicle is a doubly-curved long bone (the only horizontal long bone in the human 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 has a rounded medial end and a flattened lateral end.

From the roughly pyramidal sternal end, each clavicle curves laterally and posteriorly 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 lines and tubercles. These surface features are attachment sites for muscles and ligaments of the shoulder.

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 (arm) 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 physical 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. It is a dermal bone derived from elements originally attached to the skull.

Attachments
Muscles and ligaments that attach to the clavicle include:

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

 * acromioclavicular dislocation
 * sternoclavicular dislocations
 * clavicle fractures
 * osteolysis
 * degeneration of the clavicle