Ankle injury may involve bones or ligaments - or a combination of the two
The talar dome surface should be carefully viewed following ankle trauma
Three bones form the ankle joint - tibia, fibula and talus. Ankle fractures are usually bony injuries involving the distal tibia (medial malleolus) or distal fibula (lateral malleolus). Occasionally the articular surface of the talus can be injured.
Anterior-Posterior (AP) and Lateral. The AP or 'mortise' view is not a true Anterior-Posterior projection but rather at an angle to optimise visualisation of the ankle joint without being overlapped by the fibula.
Carefully following the bone contour of the tibia and fibula shows the inferior edge of the medial and lateral malleoli
Ankle ligament anatomy
Ankle injuries may involve bones or ligaments in isolation, or a combination of bones and ligaments. X-rays directly visualise bone injury, but understanding of the anatomical position of ligaments is required to appreciate the presence of ligament injuries which are not directly visualised.
The ankle is stabilised by multiple ligaments not visible with X-ray
Fractures of the medial or lateral malleoli can lead to ankle joint instability and loss of normal ankle joint alignment. The posterior edge of the distal tibia is sometimes referred to as the 'posterior malleolus'.
Ligamentous injury may also lead to instability of the joint, but this is not always appreciated if there is no displacement.
Lateral malleolar fractures are categorised according to their position in relation to the distal tibiofibular syndesmosis at the level of the ankle joint.
2 - Lateral malleolus fracture - proximal to the ankle and extending up the fibula (Weber C fracture)
3 - Posterior malleolus fracture
The joint is unstable and widened anteriorly (arrowheads) and at the distal tibiofibular syndesmosis (asterisk)
The talus is displaced posteriorly and laterally along with the medial and lateral malleolus bone fragments
A 'Maisonneuve fracture' is a fracture of the proximal fibula associated with injury to the medial side of the ankle and disruption of the distal tibiofibular syndesmosis. The medial ankle injury may be either a visible medial malleolus fracture or an invisible injury of the medial ligaments.
An isolated fracture of the medial malleolus, or widening of the ankle joint with no visible fracture seen on ankle X-ray, should raise the suspicion of an associated fracture of the fibula. If this is not visible in the distal fibula then further X-rays of the proximal fibula should be performed. Imaging of the proximal fibula should also be considered in the setting of any severe ankle injury or if the proximal fibula is tender to palpation.