The clavicle is a slender long 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.
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.
As a long bone, the clavicle can be divided into three parts: sternal (medial) end, shaft, and acromial (lateral) end.
The medial end of the clavicle articulates with the manubrium of the sternum at the sternoclavicular joint, while its lateral end articulates with the acromion of the scapula at the acromioclavicular joint.
The main functions of the clavicle include:
- Participation in attaching the upper limb to the trunk, by being a part of the shoulder girdle;
- Protecting neurovascular structures underneath that supply the upper limb;
- Transmitting force from the upper limb to the axial skeleton.
Sternal end of clavicle
The sternal or medial end of the clavicle has a large 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, which is a ligament that strengthens the sternoclavicular joint.
The medial end of the clavicle also gives attachment to the following structures:
- All around - to a fibrous joint capsule;
- Supero-posteriorly - to an articular disc;
- Superiorly - to the interclavicular ligament.
Shaft of clavicle
The shaft or diaphysis refers to the middle part of any long bone. The shaft of the clavicle serves as origin site for several muscles, including the deltoid, trapezius, subclavius, pectoralis major, and the sternohyoid.
Acromial end of clavicle
The acromial or lateral end of the clavicle has a facet for articulation with the acromion of the scapula to form the acromioclavicular joint. The area surrounding the joint gives attachment to a fibrous joint capsule.
The lateral end of the clavicle has landmarks that serve as the attachment sites for the coracoclavicular ligament (a ligament of the acromioclavicular joint), and these are:
- Conoid tubercle - serves as an attachment site for the conoid ligament, which is the medial part of the coracoclavicular ligament;
- Trapezoid line - attachment site of the trapezoid ligament, which is the lateral portion of the coracoclavicular ligament.