The clavicle (collarbone) extends between the sternum and the acromion of the scapula.
It is classed as a long bone, and can be palpated along its length. In thin individuals, it is visible under the skin. The clavicle has three main functions:
- Attaches the upper limb to the trunk.
- Protects the underlying neurovascular structures supplying the upper limb.
- Transmits force from the upper limb to the axial skeleton.
In this article, we shall look at the anatomy of the clavicle – its bony landmarks and clinical correlations.
Bony Landmarks and Articulations
The clavicle is a slender bone with an ‘S’ shape. Facing forward, the medial aspect is convex, and the lateral aspect concave. It can be divided into a sternal end, a shaft and an acromial end.
Sternal (medial) End
The sternal end contains a large facet – for articulation with the manubrium of the sternum at the sternoclavicular joint.
The inferior surface of the sternal end is marked by a rough oval depression for the costoclavicular ligament (a ligament of the SC joint).
The shaft of the clavicle acts a point of origin and attachment for several muscles – deltoid, trapezius, subclavius, pectoralis major, sternocleidomastoid and sternohyoid
Acromial (lateral) End
The acromial end houses a small facet for articulation with the acromion of the scapula at the acromioclavicular joint. It also serves as an attachment point for two ligaments:
- Conoid tubercle – attachment point of the conoid ligament, the medial part of the coracoclavicular ligament.
- Trapezoid line – attachment point of the trapezoid ligament, the lateral part of the coracoclavicular ligament.
The coracoclavicular ligament is a very strong structure, effectively suspending the weight of the upper limb from the clavicle.
Clinical Relevance: Fracture of the Clavicle
A function of the clavicle is to transmit forces from the upper limb to the axial skeleton. Thus, the clavicle is the most commonly fractured bone in the body. Fractures commonly result from a fall onto the shoulder, or onto an outstretched hand.
The most common point of fracture is the junction of the medial 2/3 and lateral 1/3. After fracture, the lateral end of the clavicle is displaced inferiorly by the weight of the arm, and medially, by the pectoralis major. The medial end is pulled superiorly, by the sternocleidomastoid muscle.
The suprascapular nerves (medial, intermedial and lateral) may be damaged by the upwards movement of the medial part of the fracture. These nerves innervate the lateral rotators of the upper limb at the shoulder – so damage results in unopposed medial rotation of the upper limb – the ‘waiters tip’ position.