Most broken bones don't shatter. That's very rare. Researchers have figured out why it doesn't do that, and it is because our bones are filled with goo.

Researchers at the University of Cambridge have discovered that much of the mineral content from which bones are made, is made in the form of goo. It is trapped between tiny crystals, lubricating them and allowing for small movements.

That flexibility stops our bones from shattering, which is a good thing, really.

The goo is made from citrate—a by-product of cell metabolism—mixed with water. There's enough of it to provide a slip between the crystals to absorb the energy of impact that would otherwise obliterate a solid piece of crystal bone structure.

According to Dr. Melinda Duer, one of the researchers:
"Bone mineral was thought to be closely related to this substance called hydroxyapatite. But what we've shown is that a large part of bone mineral – possibly as much as half of it in fact – is made up of this goo, where citrate is binding like a gel between mineral crystals. This nano-scopic layering of citrate fluid and mineral crystals in bone means that the crystals stay in flat, plate-like shapes that have the facility to slide with respect to each other. Without citrate, all crystals in bone mineral would collapse together, become one big crystal and shatter. It's this layered structure that's been missing from our knowledge, and we can now see that without it you're stuffed."
Read the study published here: [PNAS via Cambridge University Image by Moody Man Chang under Creative Commons license]