Competence of the deltoid ligament in bimalleolar ankle fractures after medial malleolar fixation

BACKGROUND: The stability of the ankle joint is provided by the medial and lateral malleoli and ligaments. Recent studies of cadaveric ankles have demonstrated that injury to the medial structures of the ankle is necessary to allow lateral subluxation of the talus after fracture. However, cadaveric models are limited by the fracture pattern chosen for the model. We sought to investigate the competency of the deltoid ligament in vivo in patients with an operatively treated bimalleolar ankle fracture. METHODS: Twenty-seven patients with a bimalleolar ankle fracture were evaluated. In each patient, the medial malleolus was anatomically reduced and fixed. A radiograph of the ankle was then made with application of an external rotation load to the joint. All lateral malleolar injuries were then reduced and fixed. The radiographs were evaluated for restoration of the competence of the deltoid ligament according to established criteria. RESULTS: Seven (26 percent) of the twenty-seven patients had radiographically evident incompetence of the deltoid ligament after medial malleolar fixation. This finding was associated with a small medial malleolar fragment. CONCLUSIONS: In bimalleolar fractures, the medial injury may be an osseous avulsion, leaving the deltoid intact on the displaced fragment, or it may be a combination of ligamentous and osseous injury with disruption of the deep portion of the deltoid ligament.