Chapter 22

Ankle injuries are common and account for 30% of all sports injuries.1 In the emergency department (ED), ankle injuries represent 12% of traumatic injuries. Ligamentous injuries are more common than fractures by a ratio of 5:1.2 A thorough understanding of the functional anatomy, fracture patterns, and soft-tissue injuries is important to the emergency physician.

### Functional Anatomy

The ankle is composed of the distal ends of the tibia and the fibula that form a mortise into which the talus fits. The ankle has been described in the past as a hinge joint, but it more accurately resembles a saddle joint.3 The talar dome or saddle is wider anteriorly than it is posteriorly (Fig. 22–1). With dorsiflexion, the talar dome fits snugly into the ankle mortis, yielding greater stability when compared with plantar flexion (Fig. 22–2). With this in mind, it is easy to see why most ankle injuries occur when the ankle and the foot are in plantar flexion.

###### Figure 22–1.

Note that the talar dome is wider anteriorly than it is posteriorly.

###### Figure 22–2.

In dorsiflexion, the wider anterior portion of the talar dome engages the ankle mortise and little motion is permitted. With the ankle in plantar flexion, the narrow posterior part of the talar dome lies within the mortise, permitting a significant degree of inversion–eversion “play” to occur in the joint.

The only “pure” motion occurring at the ankle joint is plantar and dorsiflexion. Inversion and eversion take place at the subtalar joint formed by the talus and calcaneus. The subtalar joint is very strong, with firm ligamentous support, and the talus should always be thought of as moving with and in the same direction as the calcaneus. Because of the strength of the calcaneotalar joint, most inversion–eversion stresses injure the ankle joint rather than the subtalar joint.

To understand the disorders that occur around this crucial joint, the emergency physician must have a good knowledge of the fundamental soft-tissue structures that surround it. These structures are best divided into three “layers” surrounding the joint. The deepest layer is the capsule, which contains the ligaments of the ankle; the middle layer includes the tendons, which traverse the joint to reach the foot; and the most superficial layer is made up of the fibrous bands (retinaculi), which hold the tendons in place as they act on the foot.

#### Capsular Layer

The capsule surrounds the ankle joint. It is weaker anteriorly and posteriorly, but is strengthened laterally and medially by ligaments. The anterior ligament is thin, connects from the anterior tibia to the neck of the talus, and is commonly involved in extensive tears of ...

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