Ankle instability

Last evidence check May 2014

Principal authors Jim Barrie, Rebecca Hope and Jo Lishman

The ankle is a modified hinge joint between the tibial plafond, medial and lateral malleoli proximally and the talus distally. The inferior tibiofibular and subtalar joints are also intimately related to ankle function. The ankle joint capsule is reinforced by the anterior talofibular (ATFL), calcaneofibular (CFL) and posterior talofibular ligaments (PTFL) laterally, and by the deltoid ligament medially, of which the deep tibiotalar part (DTTL) is the most important for ankle stability. There are also anterior (AITFL), interosseous and posterior ligaments of the inferior tibiofibular joint and a posterior transverse band, the posterior intermalleolar ligament. The subtalar joint is stabilised by the lateral, interosseous and cervical talocalcaneal ligaments, and by the calcaneofibular and superficial deltoid ligaments and the inferior extensor retinaclum, which cross both ankle and subtalar joints.

ankle axis

Axis of ankle movement

The ankle dorsiflexes and plantarflexes through an axis that passes through the tips of the malleoli. As the lateral malleolus is longer and more posterior than the medial, the axis is not quite parallel to either the ground or the coronal plane. In addition, the instant axis of rotation of the ankle moves from moment to moment. Hence, as the ankle dorsiflexes, it rotates externally and vice versa. The talus is also wider anteriorly than posteriorly, so the lateral malleolus has to rotate externally by about 11deg in the course of full dorsiflexion. Damage to the syndesmosis may interfere with ankle dorsiflexion or make it painful. The rotation of the ankle (and proximal limb) in relation to a fixed foot an the ground are accommodated by the rotation of the subtalar joint. Stiffness of the subtalar joint interferes with ankle movement and smooth gait.

When weight is borne through the ankle, the talus is compressed up into the bony mortise, and the shape of the bones produces stability. Therefore, it makes no sense to prevent patients weightbearing on the ankle unless there is a significant defect in the tibial plafond. Without axial loading, the ATFL is the main stabiliser against anterior, varus and internal rotation stresses in plantarflexion and the CFL in neutral. With increasing dorsiflexion, the ligaments of the inferior tibiofibular joint probably play an increasing part in stability. The role of the deltoid ligament and particularly the DTTL in protecting against valgus and external rotation stresses is only beginning to be understood. The role of the posterior structures has had little study, probably because posterior displacement and forced dorsiflexion is an uncommon mechanism of ankle injury.