What is the clavicle?
The human clavicle or collarbone is a short bone that lies on the front of the chest (thoracic) wall. It plays an important role in connecting the upper limb to the trunk of the body. The clavicle is also the most frequently fractured bone of the upper body especially since it lies superficially.. Although it is a small bone, this clavicle is able to bear significant force mainly by the action of the numerous muscles and ligaments that attach to it, as well as the weight of the upper limb. In thinner people, the clavicle is clearly visible through the skin and its characteristic S-shaped can even be seen. It is part of the appendicular skeleton although which connects it to the axial skeleton.
Anatomy of the Clavicle
The clavicle is actually a long bone of the body although it is short in length. It has a softer trabecular tissue inside with a hard shell of compact bone. Although it is a long bone, the clavicle lacks an internal cavity (medullary cavity) where bone marrow would be housed in most long bones. It is a also flatter compared to the more rounded contour of most long bones, and is the only long bone to lie horizontally.
Similar to other long bones, the clavicle has two enlarged ends and an elongated body (shaft). The shaft is S-shaped which is an important feature for its strength.
- The inner (medial) end of the clavicle that attaches to the breastbone (sternum) is known as the sternal end. This end is roughly triangular in shape and forms a joint with the manubrium of the sternum known as the sternoclavicular joint or SC joint.
- The outer (lateral) end of the clavicle which is flat, attaches to the shoulder bone (scapula) and is known as the acromial end. It forms a joint with the acromion of the scapula which is known as the acromioclavicular joint or AC joint.
The clavicle is not a straight long bone but curved which makes it look like an elongated capital S. This shape is very important feature which gives it the strength and resilience that is needed for its different functions.
- The inner two-thirds (medially) is convex from an anterior perspective meaning that it curves outwards when viewed from the front. It then ends at the sternoclavicular joint.
- The outer one-third (laterally) is concave anteriorly meaning that it curves inwards when viewed from the front. It ends by joining with the acromion of the scapula to form the acromioclavicular joint.
The clavicle is a major site for the attachment of as many as ten muscles and ligaments on one its four surfaces – superior (top), front (anterior), posterior (back) and inferior (bottom). The attachments for the different muscles and ligaments are as follows :
- Top (superior surface) – deltoid muscle and trapezius muscle.
- Bottom (inferior surface) – subclavius muscle, conoid ligament and trapezoid ligament of the coracoclavicular ligament.
- Front (anterior border) – pectoralis major muscle
- Back (posterior border) – sternocleidomastoid muscle, sternohyoid muscle and trapezius muscle.
The levator claviculae muscle may also attach to the clavicle if it is present.
Location of the Clavicle
The clavicle is located at the top of the thoracic wall, just below the neck and to the sides of the breastbone (sternum). It lies just above the first rib on either side of the anterior (front) chest wall. The inner part of the clavicle is bound by the costoclavicular ligament to the first rib so that it does not rise with movement of the shoulder blade.
The other structures and organs around the clavicle is as follows :
- Behind and slightly below it lies the pleura and apex of each lung.
- Below it lies the first rib separated by the intercostals muscles, blood vessels and nerves.
- Above and in front of it lies the platysma muscle.
Functions of the Clavicle
The functions of the clavicle includes :
- Absorbs force to the upper limb by transferring it to the axial skeleton, particularly the ribcage.
- Suspends the scapula (shoulder blade) so that the upper limb is able to move freely for its full range of motion.
- Protects the nerves and vessels of the upper limb that pass through the cervico-axillary (neck-armpit) canal and the apex of the lung.