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Other Terms: Collar bone, Clavicula, Clavicule
The clavicle has a sinusoidal appearance with a double curvature. The medial or sternal end being concave posteriorly, while the lateral or acromial end is concave anteriorly. This is one of the more variable bones of the skeleton. It can range from a nearly straight, smooth surfaced bone to a sinusoidal, rough textured bone. It is typically smoother and straighter in females while being rougher and more curved in males. The bone forms the ventral strut of the pectoral girdle that props the shoulder joint away from the rib cage while serving as a fulcrum for muscles that produce lateral movements of the humerus. It is subcutaneous and easily palpable throughout its length. This combination of features makes it susceptible to fracture, and it is the most commonly fractured bone in the body.
The word clavicle arises from the Latin word clavis meaning key. Adding the diminutive ending -cle to this term creates the word little key, from its fancied resemblance to an ancient key.
The clavicle articulates with three bones: the sternum, the scapula, and the first rib. The sternal extremity forms an ovoid articular facet that sits in the clavicular notch of the manubrium. Just inferior to this facet is a smaller oval surface for articulation with the costal cartilage of the first rib. Laterally, an oval facet on the inferior aspect of the acromial extremity articulates with the acromion of the scapula.
The clavicle is the first bone in the human body to ossify. The ossification process is of two types - intramembranous or dermal and endochondral. Two primary centers, one more medial and another lateral, first appear in mesenchyme during the middle of the second embryonic month. Through intramembranous bone formation these two centers soon converge. This produces the shaft of the clavicle that is well established at birth. The ends of the bone preform as cartilage before endochondral ossification establishes epiphyses. An epiphyseal center forms in the sternal end anywhere between fifteenth and twenty-first year. Fusion is typically not complete until after the twenty-fifth year. A small secondary center in the acromial epiphysis appears between the eighteenth and twentieth year and fuses rapidly with the shaft.