The clavicle (collar bone) is the only bone in the upper limb and shoulder that articulates directly with the bony thorax. It runs horizontally in a subcutaneous path from the manubrium of the sternum and the first rib to the acromioclavicular joint where it articulates with the scapula. It is curved somewhat like the letter f when viewed from above, as it is convex anteriorly in its medial two thirds, and concave anteriorly in the lateral portion.
Superior surface of the left clavicle
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The anterior surface of the clavicle is easily felt bilaterally at the anterior portion of the base of the neck. Its middle third forms the inferior border of the posterior triangle, together with the posterior border of sternocleidomastoid and the anterior portion of trapezius. The acromioclavicular joint and acromion itself are usually palpable. The sternal end of the clavicle juts above the superior part of the manubrium and can be felt at the base of the jugular fossa. The supraclavicular nerves can be rolled against the bone as they cross it superiorly.
The lateral third of the clavicle tend to be flattened so that its surfaces face superiorly and inferiorly, with borders anteriorly and posteriorly. The lateral articular facet faces laterally and slightly inferiorly. There may be a small deltoid tubercle anteriorly. A quarter of its length medially from the lateral end is the conoid tubercle, with a trapezoid line running anterolaterally to the acromial apex - the coracoclavicular ligament attaches to these features.
The medial two thirds have three facets, tending to become curved in shape. Inferiorly near the sternal end is an oval depression for attachment of the costoclavicular ligament. The middle third of the inferior surface diplays a groove for attachment of subclavius. The nutrient foramen can be found at the lateral end of this groove. The sternal end is directed medially, slightly inferiorly and anteriorly. The sternal surface is four-sided.
In association with ligaments in the area, it provides primary support to the upper limb. This support relies on the acromio-clavicular joint and the coraco-clavicular ligaments. Secondary support comes from the muscles in torso, back, upper arms.
- The clavicular part of the sternocleidomastoid muscle arises from the superomedial half of the clavicle
- The deltoid arises anteriorly from the lateral third
- The clavicular head of pectoralis major arises from the anteromedial two thirds of the clavicle
- Trapezius arises posteriorly from the lateral third
- Subclavius arises from its groove in the inferior surface of the middle third
- Sternohyoid attaches to the most medial part of the posterior surface
- The costoclavicular ligament attaches to the medial end of the inferior surface
- The conoid portion of the coracoclavicular ligament attaches to the conoid tubercle; the trapezoid portion attaches to the trapezoid line
- The clavipectoral fascia attaches to the edge of the subclavian groove.
The posterior surface relates medially to:
- The lower end of the internal jugular vein
- The junction between the subclavian and brachiocephalic veins.
- The trunks of the brachial plexus
- The third part of the subclavian artery
- The suprascapular artery and accompanying vein(s).
The clavicle is the very first bone to ossify, from two primary centres towards the middle of the bone appearing at around six weeks. Cartilage appears at both ends once the primary centres have fused, about two weeks later. A secondary centre for the sternal end appears in the late teens. Ossification is largely but not entirely intramembranous. The medial and lateral masses act as growth centres as in other long bones.
The female clavicle is
- less curved
- carried with the acromial end below the level of the sternal end.
The male clavicle has acromial and sternal ends roughly level.
The clavicle is thicker and more curved in manual workers, with more obvious areas for muscle attachment.
- May be fractured.