What Happens When You Break A Bone?

Drs. Gurpreet Baht and Natalie Pang give us the insider info:

To the bone

About half of all people will break at least one bone during their lifetime, and the body’s 200+* bones come in several categories including short bones, long bones, flat bones, and irregular bones.

^{*You may have heard different numbers. Popular numbers in the public consciousness include 215 (thanks to a famous line in the movie Terminator II: Judgment Day), and 206 which is a very popular reckoning with rather sounder reasoning, but 200 is the baseline unless you’re missing some. The reason for the variation is that humans start with 270–300 bones, but many of these fuse together in infancy (for example, much of the skull and coccyx, most of which fusing is done around ages 1–2 years), resulting in a smaller total number. Another reason for variation in total number is that some people have some extra bones, which is usually a case of a harmless copying error.}

Of these, long bones tend to fracture more frequently because they usually absorb the main force of impacts such as falls. However, in the case of somebody more frail than average (so, a lot of older people, for example), hips become quite common candidates, because upon falling: a) they’re often not falling from a great height than their own, so they didn’t break a leg b) they weren’t quick enough to put an arm out to try to break their fall, which means, if falling sideways, which there’s a 50% chance of being the case, the hip hits the floor full-force.

Some quick notes on the physiology going on here:

• On why it hurts quite so much: bones contain blood vessels and nerves that transmit intense pain signals during fractures, though scientists still don’t fully understand why broken bones hurt so much because these nerves are encased in hard tissue and difficult to study.
• On how healing gets going: when a bone breaks the internal blood vessels rupture, causing bleeding and inflammation that begin the healing process.

That process is a several-stage affair:

1. Inflammatory phase: during roughly the first week immune cells clear damaged tissue and release signalling molecules that recruit stem cells to the injury site.
2. Cartilage callus formation: recruited stem cells become chondrocytes that use the blood clot at the fracture site as a scaffold to quickly build a temporary cartilage callus.
3. Bony callus formation and remodeling: some chondrocytes and stem cells become osteoblasts that create a stronger bony callus, after which specialized cells gradually reshape the bone over several months while osteoblasts lay down new bone tissue.
4. Treatment and healing variability: healing time depends on factors such as diet, rest, and fracture severity, with clean breaks often treated using casts or splints while severe or displaced fractures may require surgery with pins, plates, or screws.
5. Misaligned healing and final outcome: if a bone heals incorrectly surgeons may need to refracture and realign it, and although a small bump may remain temporarily after healing the bone typically becomes as strong as it was before.

For more on all of this, plus some visual illustrations, enjoy:

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Want to learn more?

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Take care!