Ankle fractures are one of the most common injuries to the lower extremity. The injuries are almost always due to a twisting injury, where the foot is planted flat on the ground and the leg is forced in a twisting or sliding pattern. Ankle fractures are a frequent occurrence in high impact sports, as well as from everyday-type injuries. The anatomy of the ankle helps to define this injury, and a number of structures are at risk.
The ankle joint is composed of the tibia and fibula, which are the bones of the lower leg, as well as the talus, which is a bone of the foot. The tibia and fibula join at the syndesmosis, a structure that is key in holding the ankle in place. The tibia and fibula form a groove for the talus to move through, ensuring stability through range of motion at the ankle. A number of ligaments hold these structures together, mainly the lateral ankle ligaments and the medial ankle ligaments. The medial ankle ligaments are commonly referred to as the deltoid ligament.
A series of tendons run across the joint from the leg into the foot. These tendons belong to muscles that control the movement of the foot, including plantarflexion (pointing the foot in a downward position), dorsiflexion (bringing the foot upwards), inversion, and eversion. There are also a number of arteries, veins, and nerves that run across the ankle joint that provide blood and sensation to the foot.
Injuries to the ankle, as common as they are, can be described by several different classification systems. The two most commonly used are the Lauge-Hansen and Danis-Weber systems.
The Lauge-Hansen system classifies ankle fractures based on the mechanism of injury, taking into account both the position of the foot at the time of injury as well as the movement of the leg. For example, one of the categories for the classification is supination-external rotation. The first term denotes that the foot was in a supinated position at the time of injury. The second term indicates that the leg was externally rotated in relation to the foot, causing the injury. The four categories originally described by Lauge-Hansen included supination-external rotation (the most common mechanism of ankle fracture), pronation-external rotation, supination-adduction, and pronation-abduction. Another category was later added, pronation-dorsiflexion, indicating that the force causing the injury was an axial force through the bottom of the foot that would drive the talus bone up through the tibia. This, however, is more appropriately addressed as a pilon fracture.
Within each category of Lauge-Hansen mechanism, there are different stages indicating how extensive the damage is to the ankle joint. These stages correlate with the ankle structures effected by the injury. Shown in the diagram above, starting from top left and moving clockwise, are the supination-adduction, pronation-abduction, pronation-external rotation, and supination-external rotation injuries. The stages indicate the structures involved.
Another commonly used classification system for ankle fractures is the Danis-Weber classification. This is based on the anatomy involved in the injury, particularly the tibia-fibula syndesmosis, which is the joint between the two bones. The classification is based on the level of the fibular fracture associated with the injury. If the fracture is below the level of the syndesmosis, it is considered a type A injury. Type B would be at the level of the syndesmosis, and type B would be above the level. Danis-Weber classification helps to indicate the amount of damage to the tib-fib syndesmosis. Levels B and C are associated with damage to the joint, which may lead to instability of the ankle if not addressed during the treatment of the fracture.
The classification of ankle fractures is a very academic topic, and is used primarily to communicate between physicians treating the injured patient. Other descriptors may be beneficial in describing the injury, but the classification systems are a quick and easy way to relate what is going on with the injury between doctors and those involved. Because of the reliable patterns of ankle fractures, these classification systems are fairly universal, and have a good inter- and intra-observer reliability.
