The Clavicle
The clavicle, also called the collar bone, is a doubly curved short bone which lies horizontally in the body between the neck and the thorax, directly above the first rib. The clavicle connects the arm to the body and is important in transmission of the upper limb weight to the axial skeleton as it braces the shoulder backwards so that the arm can swing clearly away from the trunk.
Figure1: The superior surface of the clavicle
The inferior surface is grooved longitudinally in its middle third; the lateral end is flattened, while the medial end is quadrangular. The shaft is convex in its medial two-thirds and concave in its lateral third. The medial quadrangular end articulates with the clavicular notch of the manubrium sterni to form the sternoclavicular joint, it also articulates with the first costal cartilage. The lateral end is flattened from above downwards and articulates with the acromion process of the scapula to form the acromioclavicular joint.
Figure2:The inferior surface of the clavicle
The Medial two-thirds
The shaft is convex anteriorly at the medial 2/3 which has four surfaces: anterior, posterior, superior and inferior. The inferior surface has a rough area close to the sternal end for the attachment to with the costoclavicular ligament and the subclavius groove in the middle third.
The Lateral third
The lateral third is concave anteriorly and has two borders; the anterior border which is concave forwards and the posterior border which has a backwards convex curve. It also has two surfaces; the superior surface and the inferior surface which shows the conoid tubercle close to the posterior border and the trapezoidal line which extends from the conoid tubercle laterally.
Figure3: Attachment of the clavicle
Attachment of the clavicle
The following muscles are attached to the clavicle
1) Pectoralis major originates from the medial half of the anterior surface,
2) Sternocleidomastoid originates from the medial part of the upper surface,
3) Deltoid originates from the anterior border of the lateral third,
4) Trapezius is inserted into the posterior border of the lateral third, and
5) Subclavius is inserted into the subclavius groove on the middle third of the inferior surface.
2) Sternocleidomastoid originates from the medial part of the upper surface,
3) Deltoid originates from the anterior border of the lateral third,
4) Trapezius is inserted into the posterior border of the lateral third, and
5) Subclavius is inserted into the subclavius groove on the middle third of the inferior surface.
Figure4: Attachment of the clavicle