Clavicle

Where is the clavicle?

The clavicle lies nearly horizontal across the top of the chest, just above the first rib. It sits just under the skin, so you can feel it. (OpenStax A&P 2e, 8.1; Gray’s Anatomy (1918), Clavicle, p. 200; StatPearls, Clavicle Fracture)

Its medial end attaches to the sternum, part of the axial skeleton. Its lateral end meets the scapula just above the shoulder joint. (OpenStax A&P 2e, 8.1; StatPearls, Clavicle and Sternoclavicular Joint; Gray’s Anatomy (1918), Scapula, p. 202)

What does the clavicle do?

Held from above by muscles, the clavicle acts as a strut that props the scapula out to the side. That keeps the shoulder joint up and away from the trunk and gives the upper limb its freedom of motion. (OpenStax A&P 2e, 8.1; StatPearls, Clavicle)

It passes forces from the upper limb to the sternum and axial skeleton. It also shields the nerves and vessels that run beneath it between the trunk and the limb: StatPearls names the brachial plexus, the subclavian artery and the subclavian vein. (OpenStax A&P 2e, 8.1; StatPearls, Clavicle)

What are the parts of the clavicle?

The clavicle has a medial end, a lateral end and a shaft between them. The medial or sternal end is triangular. The lateral or acromial end meets the acromion, the part of the scapula that forms the tip of the shoulder. (OpenStax A&P 2e, 8.1; Gray’s Anatomy (1918), Clavicle, p. 200; StatPearls, Clavicle and Scapula)

The clavicle starts to ossify before any other bone in the embryo, yet its growth plates may not close until age 20 to 25. Its two ends ossify from a cartilage model; the shaft forms bone with no cartilage first. (StatPearls, Clavicle)

Blood reaches it through the suprascapular, thoracoacromial and internal thoracic arteries. Studies have found a supply through its periosteum and no central nutrient artery. (StatPearls, Clavicle)

Which joints and muscles does the clavicle have?

Its sternal end meets the manubrium of the sternum at the sternoclavicular joint, the only bony joint between the pectoral girdle and the axial skeleton. The joint lets the clavicle and scapula move up and down and forward and back with the shoulder. (OpenStax A&P 2e, 8.1; StatPearls, Shoulder; Gray’s Anatomy (1918), Sternoclavicular joint, p. 313)

The costoclavicular ligament ties the underside of the sternal end to the first rib; OpenStax says it supports the sternoclavicular joint indirectly, StatPearls calls it the joint’s primary restraint, and Gray’s Anatomy (1918) counts it among the joint’s ligaments. At the other end, the acromioclavicular joint with the acromion takes its main support from the coracoclavicular ligament, which ties the coracoid process of the scapula to the underside of the clavicle. (OpenStax A&P 2e, 8.1; StatPearls, Sternoclavicular Joint and Acromioclavicular Joint; Gray’s Anatomy (1918), Acromioclavicular joint, p. 315 and Sternoclavicular joint, p. 313)

On the lateral third, the deltoid attaches in front and the trapezius behind. The sternocleidomastoid attaches to the upper surface of the medial third. On the medial two-thirds, the subclavius sits in the groove beneath, the pectoralis major in front and the sternohyoid behind. (StatPearls, Clavicle)

Why does the clavicle break so often?

A fall onto the side of the shoulder causes most clavicle fractures, 87 percent of reported cases in StatPearls; a direct blow or a fall onto an outstretched hand causes fewer. The middle third breaks in about 69 percent of cases, while injury to the sternoclavicular joint is rare, 3 to 5 percent of shoulder girdle injuries. (OpenStax A&P 2e, 8.1; StatPearls, Clavicle Fracture and Sternoclavicular Joint)

OpenStax says the vessels and nerves under the clavicle seldom suffer in a fracture, because the broken bone moves forward. StatPearls still lists brachial plexus and subclavian vessel injury among the complications, since both lie close to the middle of the bone, and calls for a complete neurovascular examination. (OpenStax A&P 2e, 8.1; StatPearls, Clavicle Fracture)

How does the clavicle differ between people?

Clavicles differ by sex: men’s are usually longer, thicker and more curved than women’s. (OpenStax A&P 2e, 8.1; StatPearls, Clavicle)

Cadaver studies have measured left clavicles longer than right ones. In the rare genetic disorder cleidocranial dysplasia, the clavicles can be missing on both sides or partly missing. (StatPearls, Clavicle)

Where the sources differ

OpenStax calls the clavicle the bone fractured most often in the body. StatPearls calls it one of the bones fractured most often. (OpenStax A&P 2e, 8.1; StatPearls, Clavicle)