Extremity CT and ultrasound in the assessment of ankle injuries: occult fractures and ligament injuries

Abstract

Objective: To assess the rates of fractures and ligament injuries in patients with an acute ankle injury and a normal radiographic examination, and to consider the most appropriate examination protocol.

Methods: Patients with an acute ankle injury who presented to the John Radcliffe Hospital Emergency Department with a normal radiographic examination were eligible for the study. They were invited to receive a cone beam CT and ultrasound examination at a local radiology department within 5 days of their ankle injury.

Results: Of the 100 patients recruited to the study, 19 patients were found to have major fractures and 42 patients had small avulsion fractures. Additionally, 42 patients had ankle effusions and there were a large number of soft tissue injuries. There were 83 acute injuries of the anterior talofibular ligament, 19 of the anterior tibiofibular ligaments, 26 of the calcaneofibular ligament, 39 of the deltoid ligament complex, 21 of the talonavicular ligament, 14 of the spring ligament and 3 of the calcaneocuboid ligament.

Conclusion: Conventional radiographic examination misses significant fractures of the foot and ankle and the presence of an ankle effusion does not relate to the severity of injury. Ultrasound is a useful imaging technique that can supplement clinical practice, but it is unlikely to replace current protocols alone. Cone beam CT is an appropriate alternative to plain radiography, being more sensitive in detecting fractures and delivering a similar dose of radiation. However, neither CT or ultrasound examination can detect all avulsion fractures. Simple anterior process fractures of the calcaneus are associated with talonavicular ligament injuries and the medial ligaments are injured in almost 50% of cases when there is a lateral ligament injury.

Advances in knowledge: Fractures in the foot and ankle are detected more precisely with cone beam CT compared to radiographs. Cone beam CT delivers similar doses of to conventional radiographs which is around 10% of that resulting from conventional CT. Ultrasound examination is an effective assessment tool to detect ligamentous injuries. The absence of an ankle effusion does not exclude a major fracture.

Figure 1.

The use of fusion imaging to correlate between an ankle CT and ultrasound. (1a) Picture of ultrasound machine in use for fusion imaging. (1b) Image of an anterior ankle with fusion of the CT and ultrasound.

Figure 2.

A fracture of the posterior malleolus of the tibia seen on CT (2a) and ultrasound with a deltoid ligament rupture (2b) in the same patient (arrow).

Figure 3.

Calcaneus (3a) (arrow) and navicular fractures (3b) (arrow) seen in the same patient on CT.

Figure 4.

A patient with an anterior process of the calcaneus fracture (4a) but also a cuboid fracture (4b) and a talar process fracture (4C) (arrowed).

Figure 5.

The same patient as in four showing the cuboid fracture on ultrasound as well as CT (arrows).