The fibula is the thinner of the two bones in your lower leg, running from your knee to your ankle alongside the larger tibia. While the tibia (your shin bone) carries most of your body weight, the fibula provides stability and serves as an attachment point for muscles that move your foot and ankle.

You can remember which bone is which because the fibula sounds a bit like “fib,” as in a small lie, and it's the smaller, more slender bone of the pair.

The fibula matters more than you might think. Without it, your ankle would be unstable, and you'd struggle to move your foot properly. Athletes who break their fibula often need several weeks to heal before they can run or jump again. The bone also helps protect the delicate nerves and blood vessels in your lower leg. When doctors examine an X-ray of a broken leg, they check both the tibia and fibula to see which bones need treatment.