The purpose of this study was to describe the incidence of plafond impaction in supination-adduction type II (SAD-II) ankle fractures and assess the accuracy of plain radiographs in detecting plafond impaction and predicting planned operative management compared to computed tomography (CT).

Patients with SAD-II ankle fractures were retrospectively identified. All SAD-II plain radiographs were reviewed (120 fractures) and compared to CT images (55 fractures). For each plain radiograph or CT scan, 3 orthopedic surgeons were asked the following questions: (1) Is there impaction of the tibial plafond? (2) Does the impaction require direct visualization and articular reduction? The incidence of plafond impaction and the preoperative plan were calculated separately for plain radiographs and CT scans. The accuracy of plain radiographs was calculated using responses from corresponding CT imaging as the gold standard. Change in preoperative management decisions after reviewing CT images was also calculated.

In 120 SAD-II ankle fracture plain radiographs, marginal impaction of the plafond was visualized in 61% of fractures. The diagnosis of impaction using plain radiographs was correct in 84% of fractures when compared to CT imaging, resulting in a 91% positive predictive value (PPV) and a 55% negative predictive value (NPV). Plain radiographs were able to predict planned operative management after review of CT imaging with an 87% PPV and 75% NPV.

The majority of SAD-II ankle fractures involved marginal impaction of the tibial plafond. Plain radiographs were accurate in diagnosing impaction when it was present, but were not accurate in ruling out impaction. In the presence of impaction, CT likely will not change planned operative management.

Level III, comparative series.