Ankle Instability

Anatomy

The lateral ankle ligament complex is composed of the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL). The ATFL runs from the distal fibula to the talar neck and is the primary restraint to anterior displacement on the tibia. It functions to restrict ankle inversion, particularly in plantarflexion. It is the weakest lateral ankle ligament and is most commonly involved in lateral ankle sprains. The CTFL is the primary ligamentous restraint to ankle inversion in dorsiflexion and is injured in at least half of all lateral ankle sprains. It runs from the distal fibula to the lateral calcaneus. The PTFL extends from the posterior fibula to the lateral talus. This ligament is injured in 10% of lateral ankle sprains.

The medial ankle ligament (deltoid ligament) is the strongest ankle ligament. It arises from the medial malleolus of the tibia and inserts at multiple sites, including the calcaneus, the talus, and the spring ligament of the foot.

Dynamic stability is provided by the peroneal muscles on the lateral side of the ankle. These muscles function as evertors. Medially, the tibialis posterior muscle aids in hindfoot inversion and medial ankle stability.

Etiology

The position of the ankle at the time of the sprain determines the pattern of ligament injury. Lateral ankle sprains result from inversion and internal rotation of the foot on an externally rotated leg. In plantarflexion, the ATFL is usually injured in isolation. In dorsiflexion, both the ATFL and the CFL may be injured.

Medial ankle ligament injuries are much less common than lateral ankle injuries. Isolated medial injuries typically occur as a result of excessive hindfoot eversion, as in dancing, landing on an uneven surface, or running down stairs. Often patients are predisposed to injury by valgus alignment of the hindfoot and/or tibialis posterior tendon dysfunction.

In some chronic ankle injuries, patients can present with both medial and lateral ankle instability.

Chronic ankle instability is characterized by persistent pain, recurrent sprains, and repeated instances of the ankle giving way. While the etiology of chronic instability is multifactorial, a history of primary ankle sprains is a major contributor. Chronic ankle instability can arise as a result of pathologic laxity, degenerative changes, strength deficits, impaired proprioception, and/or poor neuromuscular controls. (See the entry Ankle Instability, Chronic.)

History

Acute ankle sprains typically present with an inversion-type injury associated with sports participation, a slip and fall, or other traumatic event. Patients complain of pain, stiffness, and swelling at the ankle, worsened by weight bearing. Depending on the severity of the injury, the patient may be unwilling to weight bear on the limb.

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