Anatomy of Ankle stability in ankle fracture
The major determinant of an ankle’s stability is a derivative of the osseous configuration of the ankle joint. The bony anatomy that confers stability is composed of the distal end of the tibia and fibula and their articulation with both each other and the talus. In the ‘neutral’ ankle position, also referred to as the closed pack position, the congruence of the bony architecture of the medial and posterior projections of the tibia (medial and posterior malleoli) and the fibula with the widest part of the talar body gives it its greatest stability.

The ankle joint functionally is dependent on the articulations of the subtalar joint and talocalcaneonavicular joint as each of these articulations have a number of common ligamentous stabilisers and work synergistically in the movement of the hind-foot. The superficial deltoid ligament (consisting of the spring ligament, tibionavicular ligament, and tibiocalcaneal ligament) controls the proximal aspect of the medial longitudinal arch along with talar translation in the frontal plane. Injury to the superficial complex should not be underestimated as early mobility on such an injury may predispose to flatting of the medial longitudinal arch, even with the ankle congruency being intact. The deep deltoid, consisting of the anterior tibiotalar ligament and the posterior tibiotalar ligaments, control the talar tilt and lateral translation.

The posterior deep deltoid is the shortest and thickest component of the deltoid ligament complex, and restrains rotation of the talus horizontal and frontal plane, however its action is not apparent unless the foot is in neutral to dorsiflexed position.The lateral ligamentous structures of the ankle are well described. The anterior talofibular ligament (ATFL) primarily resists anterior translation of the talus. With regards to the syndesmosis, the distal fibula is convex at its distal articulation with the tibial plafond, where it articulates with a complimentary concave depression on the posterolateral tibia known as the triangular fibular notch (or incisura fibularis tibiae).

There are three groups of syndesmotic ligaments; anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL) and interosseous ligament. The AITFL prevents lateral fibular translation along with the PITFL, which encompasses the intermalleolar ligament. The interosseous ligament constrains the tibia and fibula from separating along their course in the lower leg whilst allowing some small degree of rotational movement and terminates approximately 1 cm proximal to the ankle joint. The syndesmotic ligaments also confer significant rotational stability, with the AITFL preventing approximately 24% of external rotation at the ankle joint and the PITFL being shown to resist internal rotation at the ankle joint.