Trimalleolar ankle fracture with syndesmotic injury
The x-ray in this case severely underplays the severity of the ankle injury, which on MRI consists of:
- Trimalleolar fracture with undisplaced fractures of the posterior and medial malleoli as well as avulsion fractures of the lateral malleolus involving the anterior talofibular ligament.
- Syndesmotic injury with complete rupture of the anterior inferior syndesmotic ligament and hyperintensity of the interosseous and posterior inferior syndesmotic ligaments in keeping with grade 2 injuries.
- Anteromedial talar dome osteochondral injury with subchondral fracture.
Occult ankle fractures are uncommon and it is difficult to maintain a high level of suspicion with most ankle x-rays negative for fracture (between 2.5-20% are positive for fracture depending on clinical setting, being highest in emergency department referrals). Medial/lateral ankle soft tissue swelling does not help pick up occult fractures but an ankle joint effusion of >13-15 mm (measuring anterior and posterior components perpendicular to the joint line) on a lateral radiograph without a fracture seen should prompt further referral to CT.