What we normally think of as the ankle is actually made up of two joints: the subtalar joint, and the true ankle joint. The true ankle joint is composed of 3 bones: the tibia which forms the medial, portion of the ankle; the fibula which forms the lateral portion of the ankle; and the talus underneath. The true ankle joint is responsible for dorsi and plantar flexion of the foot. .
Just below the true ankle joint is the second part of the ankle, the subtalar joint, which consists of the talus on top and calcaneus on the bottom. The subtalar joint allows eversion and inversion motion of the foot. .
The talus has a shiny joint surface covering which allows your ankle to glide effortlessly across the shiny undersurface of your tibia. .
The fibula helps prevent your major ankle bone from shifting outward. On the other side of the ankle is the tibia. On this side you will find a bump, just like the lateral side. This is known as the malleolus, which means hammer in Latin.
The stability of the ankle joint is dependent upon the ability of these bones to keep the central bone in place while the ankle moves. The joint is more stable when your foot is flat on the floor. The ankle is more rigidly held in place by the bony stabilizers of the fibula and malleolus because they are closer to the talus. However, when you point your toes, your ankle becomes unstable because the distance between the bony stabilizers of your ankle becomes larger. Thus, your ankle than relies more and more on the soft tissues including your ligaments to continue to provide stability. Since soft tissues are "softer" than your bones, you become more vulnerable to a "sprain" when you are pointing your toes.
There are six major soft tissue structures that hold the ankle in place. Four of these are located on the outside part of your ankle and all attach to your smaller ankle bone called your fibula. Thus, all three of these ligaments have the word fibula in them.