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