Ankle Dislocation

Excerpt

Ankle dislocations are a relatively common type of dislocation encountered in the emergency department. They exist in two forms:

1. a true dislocation without fracture

2. a fracture-dislocation, occurring in the vast majority

The ankle joint complex is composed of three main articulations: talocalcaneal (subtalar), transverse-tarsal (talocalaneonavicular) and the tibiotalar (talocrural) joints. The true ankle joint is the tibiotalar joint (between the tibia, fibula and the talus). It is a ring-like structure with the ability to plantarflex and dorsiflex 40° and 20° respectively in the sagittal plane. It is a hinge joint. Below the ankle, at the subtalar joint (joint between the talus and calcaneus), the foot can typically invert 23° and evert about 12° in the frontal plane. The transverse tarsal joint (Chopart’s joint) is the junction between the talus and navicular bone. Because they share a common axis of motion, the transverse tarsal joint and the subtalar joint are considered part of the same functional unit with the motions of inversion and eversion. The combination of these joints gives the foot the ability to compensate for the loads placed during walking and other activities.

The human ankle maintains this range of motion under extremely heavy loads and can support several times the human body weight for short periods. Because of the stress placed on the ankle as one pushes off in different directions, it is possible to dislocate it by exceeding the ligamentous strength that encloses the ankle.

The stability of the joint is maintained through three groups of ligaments: the tibiofibular syndesmosis, the deltoid ligament, and the lateral collateral ligaments. The tibiofibular syndesmosis limits motion between the tibia and fibula and is composed of the anterior tibiofibular ligament, posterior tibiofibular ligament, and the interosseous tibiofibular joint. The deltoid ligaments support the medial ankle and aid in resisting eversion. The lateral collateral ligaments (including the anterior and posterior talofibular ligaments and the calcaneofibular ligament) act to resist inversion. Usually, the ligaments are so strong that the bones give way and create a fracture-dislocation.