The fibula is on the outside of your lower leg. It runs along the lateral (outer) side of the tibia, the larger bone that forms the main structure of your shin. If you’re trying to figure out which bone is which, the easiest way to confirm this is by feeling your ankle: that bony bump on the outside of your ankle is the bottom end of your fibula.
Where Exactly the Fibula Sits
The fibula starts just behind the outer edge of your knee and runs all the way down the outer side of your leg to your ankle. At the top, its rounded head sits slightly below and behind the tibia’s upper surface. You can feel the fibular head by pressing on the outside of your leg just below the knee joint. At the bottom, the fibula flares out to form the lateral malleolus, which is the prominent bump on the outer side of your ankle.
The tibia, by contrast, is the larger bone on the inner (medial) side. It’s the one you feel when you run your hand down your shin. Together, the two bones create a frame for the lower leg, with the tibia handling the heavy lifting and the fibula providing structural support on the outside.
How to Tell the Two Ankle Bumps Apart
Both sides of your ankle have a visible bony bump, which can cause confusion. The outer bump is the bottom of the fibula. The inner bump is the bottom of the tibia, called the medial malleolus. A quick way to remember: fibula equals the far side (both start with “f” if you think of “far” as the side away from your other leg).
If you look closely, you’ll also notice the outer bump sits slightly lower than the inner one. This asymmetry is normal and helps lock the ankle bone (the talus) into a tight pocket between the two malleoli, which is a key part of what keeps your ankle stable.
Why the Fibula Matters If It Barely Bears Weight
The fibula carries only about 6% of your body weight when your ankle is in a neutral position. The tibia handles the rest. So why does the fibula exist at all? It serves three important roles.
First, it’s an anchor point for muscles. Several muscles that control your foot and toes attach directly to the fibula, including the muscles that let you point your toes outward (eversion) and the ones that extend your toes. One of the hamstring tendons also connects to the fibular head at the knee.
Second, the fibula is essential for ankle stability. The bottom of the fibula forms the outer wall of the ankle joint. Four ligaments bind the lower fibula tightly to the tibia in a connection called the syndesmosis. This keeps the ankle socket the right width. Even a 1 millimeter widening of that socket reduces the contact area of the ankle joint by 42%, which can lead to instability and eventually arthritis.
Third, the fibula acts as a bit of a spring. During movements like pulling your foot upward, the ligaments between the tibia and fibula allow a tiny amount of separation so the wider front edge of the ankle bone can wedge snugly into the joint. This gives the ankle both flexibility and stability at the same time.
Common Fibula Injuries
Because the fibula forms the outer ankle, fractures at its lower end are one of the most common ankle injuries. Doctors classify these fractures by where the break occurs relative to the ligaments that bind the fibula to the tibia. A break below those ligaments is generally stable and often heals without surgery. A break right at the level of those ligaments may or may not involve ligament damage. A break above them is typically unstable, meaning the ligaments are torn and surgery is more likely.
At the other end, a sudden forceful contraction of the hamstring can pull hard enough on the fibular head to cause an avulsion fracture, where a small piece of bone gets yanked away at the tendon attachment. This is less common but can happen during explosive movements in sports.
The Fibula as a Spare Part
Because the fibula carries so little weight, surgeons sometimes harvest a section of it to use as a bone graft elsewhere in the body. It’s used to rebuild parts of the jaw, spine, or other long bones after trauma or tumor removal. Most people recover well after losing a portion of the fibula, though about half experience incisional pain in the short term. More serious complications are uncommon: roughly 3% develop stress fractures in the tibia afterward, and about 1% experience lasting ankle instability. The body adapts surprisingly well to functioning without a full-length fibula, precisely because the tibia does nearly all the weight-bearing work.