The clavicle (also collarbone, Latin: clavicula) is a paired long bone extending between the sternum and the scapula. The clavicle can be palpated along its length, and can is visible under the skin in a thin person.
The clavicle is slender bone with two curves, giving it an “S” shape. When facing forward, its medial part is convex, while its lateral aspect is concave. The clavicle is situated directly above the first rib. Its medial end articulates with the manubrium of the sternum at the sternoclavicular joint. The lateral end of the clavicle articulates with the acromion of the scapula at the acromioclavicular joint.
Interestingly, the clavicle is the only long bone that lies horizontally in the human body. The clavicle acts as a strut that keeps the scapula in place so that the upper limb can hang freely.
The main functions of the clavicle include:
- participates in attaching the upper limb to the trunk, by being a part of the shoulder girdle;
- protects neurovascular structures underneath that supply the upper limb;
- transmits force from the upper limb to the axial skeleton.
The clavicle can be divided into three parts: a sternal (medial) end, a shaft, and an acromial (lateral) end.
Sternal end of clavicle
The sternal or medial end of the clavicle has a large triangular facet for articulation with the clavicular notch on the manubrium of the sternum. This articulation forms the sternoclavicular joint.
The inferior aspect of the medial end is marked by a rough oval depression for the attachment of the costoclavicular ligament. It is a ligament of the sternoclavicular joint.
The medial end also gives attachment to the following structures:
- all-around - a fibrous joint capsule;
- superoposteriorly - an articular disc;
- superiorly - the interclavicular ligament.
Shaft of clavicle
The shaft (or diaphysis, or body) refers to the middle part of any long bone. The shaft of the clavicle serves as an origin site for several muscles, including the deltoid, trapezius, subclavius, pectoralis major, and sternohyoid.
Acromial end of clavicle
The acromial or lateral end of the clavicle has an oval facet for articulation with the acromion of the scapula to form the acromioclavicular joint. The area surrounding the joint gives attachment to the fibrous joint capsule.
The lateral end of the clavicle has landmarks that serve as the attachment sites for the coracoclavicular ligament:
- conoid tubercle - attachment site of the conoid ligament, which is the medial part of the coracoclavicular ligament;
- trapezoid line - attachment site of the trapezoid ligament, which is the lateral part of the coracoclavicular ligament.
The coracoclavicular ligament is a very strong ligament that connects the clavicle with the coracoid process of the scapula. It suspends the weight of the upper limb from the clavicle.