Overview:
The human clavicle is considered to be a ‘key’ like structure and is said to be a long bone of the body although there are several differences from a classical long bone and the clavicle. It extends from the sternum in the front of the chest to the shoulder joint at its lateral end. By having such an arrangement, the clavicle is able to keep the upper limbs away from the axial skeleton or the thoracic cage and therefore provide maximum mobility to the shoulder joint. It further supports the keeping of the scapulae bone in place and provides much needed attachment surface to the muscles of the chest wall and shoulder girdle.
Anatomy:
When considering the anatomy of the clavicle, it can be said to have two curves which gives it the features that looks like a ‘key’. At its sternal end, the clavicle has a pyramidal cross section whereas in the lateral end it becomes flattened. The medial one third of the clavicle directs laterally and anteriorly whereas the lateral two thirds would be directed laterally and posteriorly. On the undersurface of the lateral end there is a rough surface to be attached with the acromian process of the scapulae. On its surface, rough areas for the attachment of muscles of the shoulder, neck and the chest wall will be present.
Ossification:
When considering its origin and ossification, the clavicle is one of the earliest bones to start ossifications but would be very late in completing the process. Thus, during the 5th and 6th week of gestations, the bone would start ossification through a process called membranous ossification and the completion of this process would be around the ages of 21 – 25. Following ossification, there would be two types of bones namely, the cancellous bone in the center and compact bone as a surrounding layer. The cancellous bone would be ossified with two ossification centers which would be fused later and the compact bone is ossified through the surrounding fascia which would ossify the adjacent tissues through a process known as periosteal ossification.
Clinical features:
The clavicle, due to its fragile nature at time of birth, is prone to fractures when certain obstetric practices are used and teenagers and young adults can also commonly present such fractures following sports related injuries and after a fall against an outstretched hand. Due to the relative weakness at the site between the middle one third and the lateral two thirds, the fractures would commonly occur at this site.
Another feature that can be seen following a clavicle fracture is the disposition of the fractured segments due to the muscle attachments. Thus, the medial end is displaced upwards and medially as the neck muscles would be pulling this segment upwards. In contrast, the un-opposing action of the shoulder muscles would pull the lateral segment downwards and backwards and thereby make the shoulder drop on the affected side.
