The clavicles, or collarbones, are a pair of long bones that connect the scapula to the sternum. The name clavicle comes from the Latin word for “little key” and describes the shape of the clavicle as an old-fashioned skeleton key. The clavicle is one of the most commonly broken bones in the human body. It also serves as an important and easily located bony landmark due to its superficial location and projection from the trunk.
The clavicles are cylindrical bones around 6 inches (15 cm) long and curved in the transverse plane like a letter S. They are located in the thoracic region superior and anterior to the first rib. Each clavicle runs transversely and forms a joint with the sternum on its medial end and the scapula on its lateral end. The medial end of each clavicle is a smooth, rounded cylinder known as the sternal extremity, which forms the sternoclavicular joint with the manubrium of the sternum. Viewed from the anterior position, the clavicle forms a convex curve at its medial end before forming a smaller concave curve near its lateral end. The lateral end terminates in a flattened facet known as the acromial extremity, which forms the acromioclavicular (AC) joint with the acromion process of the scapula.
The clavicles, along with the scapulae, form the pectoral girdle that attaches the bones of the arm to the trunk. In fact, the sternoclavicular joints are the only bony attachments between the pectoral girdles and the bones of the axial skeleton. The clavicles function as struts to anchor the arms to the trunk while permitting the movement of the scapulae and shoulder joints relative to the trunk. The movement of the clavicles increases the mobility of the shoulder joints beyond what would be possible with only ball-and-socket joints, allowing the arm to move in a large circle. Several muscles of the neck and shoulder also attach to the clavicle, including the pectoralis major, sternocleidomastoid, trapezius, and deltoid.
The unique position of the clavicle in the body frequently makes it the site of fractures from several types of accidents. When the arm is extended to break a fall, much of the force from the fall is transmitted through the arm to the shoulder, which shifts suddenly and can fracture the clavicle. When a strong force is applied directly to the shoulder, such as during a car accident, tackle, or sudden fall, the shoulder bones can be pushed medially and result in a fractured clavicle.