collarbone
Meaning of collarbone: The only bony strut holding the arm away from the chest, and one of the most frequently broken bones at any age.
Definition of collarbone
The collarbone is the slender S-shaped bone that runs across the top of the chest from the breastbone to the shoulder blade. A pair of them sits just under the skin at the base of the neck, easily felt along their whole length. Each one props the shoulder outward from the trunk and transmits force between the arm and the central skeleton.
What does it connect?
It is the only bone that joins the arm to the rest of the skeleton. At the inner end it meets the breastbone at a small joint sitting in the hollow at the base of the throat. At the outer end it meets a bony shelf on the shoulder blade. Everything else holding the shoulder in place is muscle and ligament, which is why the shoulder moves through such a wide range and why it dislocates so readily. The medical name for the same bone is the clavicle.
Why does it break so often?
Force travelling up the arm from an outstretched hand, or a direct fall onto the point of the shoulder, is funneled into a thin curved bone with almost no muscle padding over it. The middle third is the usual break site, since that is where the two curves meet and the cross section is narrowest and least supported. Breaks here are common in cycling and contact sport, and also in newborns after a difficult delivery, where the bone heals fast and often goes unnoticed. Healing usually leaves a visible or palpable lump of new bone.
How do the two ends differ?
| Part | Joins | What goes wrong there |
|---|---|---|
| Inner end | Breastbone, at the throat | Rarely injured; dislocation can press on structures behind it |
| Middle third | Nothing; an unsupported span | The commonest fracture site |
| Outer end | Shelf of the shoulder blade | Separated shoulder, where the ligaments tear |
Why does its position matter?
Large blood vessels and the bundle of nerves supplying the arm pass directly beneath it on their way from the neck into the armpit. The bone shields them, but a displaced fragment sits close enough to threaten them, which is one reason a break is assessed for numbness or weakness in the hand rather than for shoulder pain alone. Lymph nodes above and below the bone drain the chest and abdomen, so a firm node felt there is treated as a finding needing explanation rather than a local problem.
Also known as
Used in a sentence
The collarbone was fractured in the middle third with minimal displacement.
Good to know
The nerves and blood vessels supplying the arm run immediately behind the bone, so a displaced fracture is assessed for numbness, weakness or altered circulation in the hand as well as for the break itself.