Laboratory Studies
No routine laboratory studies are indicated in patients with an ankle fracture unless syncope or other medical conditions are involved.
Imaging Studies
Radiographs in patients with a suspected ankle fracture should include anteroposterior, lateral, and mortise views (which are taken with the foot internally rotated 15-20°). [10, 11, 12, 13] The mortise view eliminates the overlapping shadow of the tibia on the fibula.
Stress-view radiographs have a limited role in evaluating an acute ankle injury. They should only be taken while a patient is under anesthesia before reconstructive surgery. A standing mortise view of the ankle can help identify ligamentous instability in patients who are difficult to examine. Comparison of the normal radiographic relationships from the mortise and standing mortise views shows loss of the normal tibiofibular overlap and asymmetry of clear spaces. A comparison view with the uninjured ankle can be useful in difficult cases.
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When reviewing ankle radiographs, consider that transverse fractures usually result from avulsion forces, whereas oblique fractures (usually fibular) generally result from torsional stress of the talus against the malleolus. Vertical malleolar fractures are secondary to an impact on the talus. Any displaced malleolar fracture should be considered unstable, and they are almost always associated with ligamentous injury of the opposite side. In general, all displaced medial malleolus fractures and oblique fibular fractures that are 2-3 inches proximal to the joint line should be assumed to have associated ligament injury and should be considered unstable.
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In addition to using the radiographic guidelines of alignment, bone, and connective tissue to evaluate ankle radiographs, checking for the 5 most commonly missed foot and ankle fractures is advised. Close attention to the fifth metatarsal base, lateral process of the talus, os trigonum or posterior malleolus, anterior process of the calcaneus, and talar dome (forming the mnemonic FLOAT) can help clinicians correlate radiographic findings with tenderness upon physical examination.
The radiographic relationships of the ankle mortise view are as follows:
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A lateral clear space of more than 2 mm suggests a syndesmosis sprain.
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The normal tibiofibular overlap is greater than 1 mm.
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The normal medial clear space is less than 4 mm or a difference from medial to lateral of less than 2 mm.
Radiographic relationships of the anteroposterior ankle view are as follows:
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A medial clear space of more than 3 mm may indicate deltoid ligament or syndesmosis injury.
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The tibiofibular space is normally less than 6 mm.
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In the standing anteroposterior view, syndesmotic widening of greater than 3 mm indicates syndesmotic sprain.
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Diagram showing the typical locations for ankle fractures occurring from the 4 major injury mechanisms (SA= supination adduction, SE= supination external rotation, PA= pronation abduction, PE= pronation external rotation). Note that the SE fracture is shown as a dashed line, since it is best seen in the lateral projection.
