The standard plain radiographic views of the injured ankle are the mortise view and lateral. The mortise view is a modified AP with the ankle internally rotated so that the malleoli are in the same horizontal plane and the joint space is seen evenly on both sides of the ankle. This requires 10-20deg internal rotation. Adding a true AP view does not add useful information and should not be part of the standard series. We obtain ankle Xrays weightbearing when possible, but in the acute trauma situation the patient usually cannot comply fully.
The Ottawa ankle rules (Stiell et al 1994) have been shown to be accurate in predicting the need for radiography in the acute trauma situation. They can be used accurately by medical and nursing staff in a variety of settings, and can reduce unnecessary radiography. However, like many decision aids, their main function may be to ensure the practitioner carries out a proper clinical assessment.
Fractures with an unusual configuration or major plafond fragments may benefit from a CT to aid planning reconstruction
In the mortise view, the ankle joint “clear space” should be even on both sides of, and above, the talus. Lateral talar translation of more than 2mm is thought to imply a DTTL tear and, therefore, instability. However, Schuberth et al (2004) found that medial clear space was a poor predictor of arthroscopically-diagnosed deltoid injury.
On the mortise view, there is normally an overlap of at least 1mm between the fibula and the tibia (Pettrone et al 1983, Brage et al1997). Reduction of the overlap indicates syndesmotic instability.
The distal fibular fragment in AO B and C fractures is externally rotated relative to the proximal fragment. In stable fractures with an intact deltoid ligament, the distal fibular fragment is congruent with the talus and the mortise is congruent; the apparent external rotation is due to internal rotation of the proximal fragment by muscle action (Magid et al 1992, Harper 1995). However, in unstable injuries with a deltoid tear or medial fracture, the distal fibular fracture is truly externally rotated and the medial clear space is increased (Tang et al 2003).
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