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Ankle Anatomy

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The ankle is an excellent example of interplay between bone and ligamentous structures and their protective relationship upon one another. The ankle joint is maintained by the shape of the talus (first bone of the foot) and its tight fit between the tibia and fibula. In the neutral position, there are strong bony constraints. With increasing plantar flexion, the bony constraints are decreased and the ligaments are more susceptible to strain and injury. The three major ligament groups that support the ankle include the tibiofibular ligaments, the deltoid ligament complex medially and the lateral ligament complex.

LATERAL ANKLE LIGAMENTS:

The lateral ligament complex of the ankle consists of three separate ligaments: the anterior talofibular ligament, the posterior talofibular ligament and the calcaneofibular ligament. These ligaments stabilize the ankle, and serve as a guide to direct ankle motion.

Figure 14 The primary function of the anterior talofibular ligament is to restrain anterior displacement of the talus in respect to the fibula and tibia. It assumes a course parallel to the axis of the leg when the foot is plantar flexed (pushed down) and thereby functions as a collateral ligament. Because most sprains occur when the foot is in plantar flexion, this ligament is most frequently injured when the foot inverted (turned in).

The calcaneal fibular ligament ligament runs from the tip of the fibula to the tubercle in the calcaneus. The primary function of the calcaneofibular ligament is to restrain inversion of the calcaneus (heel bone) with respect to the fibula. The calcaneofibular ligament and the anterior talofibular ligament play significant roles in different positions of the ankle. The calcaneofibular ligament is the main lateral stabilizer of the ankle in both neutral position and dorsiflexion. The reason that the anterior talofibular ligament is the most commonly injured of these ligaments is that the majority of the sprains occur during flexion and inversion of the foot. The anterior talolfibular ligament is usually the first to suffer disruption followed by the calcaneofibular ligament and subsequently the posterior talofibular ligament.

The posterior talofibular ligament arises from the posterior medial aspect of the lateral malleolus (fibula) and runs posteromedially to the talus. The primary function of the posterior talofibular ligament is to resist posterior displacement of the talus. This ligament is under greater strain in full dorsiflexion of the ankle. The posterior talofibular ligament is rarely torn in an ankle sprain because bony stability protects the ligaments when the ankle is in dorsiflexion.

MEDIAL ANKLE LIGAMENTS:

Deltoid Ligament:

The deltoid ligament is triangular in shape and consists of a superficial and deep layer which connect the talus to the medial malleolus.

The superficial part of the deltoid ligament consists of the tibionavicular ligament, the tibiocalcaneal ligament in the middle, and the superficial tibiotalar ligament posteriorly. The deep layer of the deltoid consists of the anterior and posterior tibiotalar ligaments. The deep layer is more important in ankle stability than superficial layer. During ankle motion all parts of the deltoid ligament function as a unit providing support to the ankle.

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