Anatomy

What structures are most commonly injured?

Three bones take part in the ankle joint: the tibia, fibula and the talus. The tibia and fibula are the bones that extend from the knee to the ankle, making up the shin; the talus is the foot bone that forms a joint with the tibia and fibula. Together these form a mortise and tenon joint, similar to that used in carpentry. The ankle allows up and down movement but very little rotation, tilt, or side to side movement. In effect the talus is locked into the ankle mortise.

The ligaments of the ankle joint are also important in the understanding of ankle fractures. There are ligaments that connect the fibula and tibia, the tibia and the talus and the talus and the fibula. Together the bones and ligaments form a ring.

A ring usually breaks in two separate regions and this is often the case in the ankle joint. If there is a break in the tibia on the inner side, one has to look for a disruption somewhere between the fibula and the talus on the outer side. This may be a torn ligament which will not show on x-ray but is important none the less. The interosseous membrane between the tibia and the fibula must be considered an ankle ligament in this context. It is often torn in ankle injuries.

If you feel your ankle you will notice that there are hard bumps of bone on the inner and outer sides of the ankle. These are called the medial and lateral malleoli. They are the lower ends of the tibia and fibula respectively. One, or both of these bony prominences may be injured in an ankle fracture. The shaft of the fibula may also be involved.

You may hear the term trimalleolar fracture being used to describe an ankle fracture. The third malleolus is the back of the tibial joint surface which can be broken in some patterns of ankle fracture. Although fractures of the malleoli enter the joint they do so outside the main weight-bearing part of the joint so it is less common for the joint surface to be badly damaged in this pattern of fracture.

In the Pilon fracture, the most severe form of ankle fracture, the joint surface of the tibia (called the tibial plafond) is broken and the weight bearing part of the joint surface may then be crushed or fragmented.

Fractures of the talus are discussed in A Patient's Guide to Adult Foot Fractures.

Related Document: A Patient's Guide to Adult Foot Fractures