O2105: Radiographic Predictors of Displacement in Transitional Ankle Fractures: Can We Avoid a CT Scan on All Patients?

Background: Transitional ankle fractures in pediatric patients are commonly diagnosed with plain radiographs. In these injuries advanced imaging with computer tomography (CT) scans are often then used to determine fracture pattern and displacement, and ultimately guide indications for management. However, pediatric CT imaging has been associated with increased lifetime radiation and cancer mortality risk. The purpose of this study was to assess the ability of radiographic measures to predict displacement on CT for transitional ankle fractures.

Methods: This study is a retrospective review of pediatric patients who presented with Salter-Harris III (Tillaux) and IV (Triplane) fractures at a single institution over a 7-year period between October 2015 and November 2022. We included all patients aged 18 and younger who had both plain radiographs and CT imaging at the time of presentation. We excluded patients with ipsilateral lower extremity fracture. Radiograph and CT measurements were performed by three independent evaluators, and interclass correlations were calculated to measure interobserver reliability. Spearman correlations were utilized to assess the correlations between each radiographic parameter and CT measurements.

Results: This study included 61 patients. The average age of patients was 12.3 and 66% of patients were male. The majority of injuries were associated with a fall (69%), followed by sports (28%). There was an almost even split of triplane (55.7%) and Tillaux (44.3%) fractures with more patients receiving surgical intervention (59.0%). The majority of measurements showed substantial interobserver agreement (ICC>0.5). Radiographic AP view showed the least reliable measurements compared to mortise and lateral views. There was significant correlation between CT displacement and the following measures on radiographs: tibiofibular clear space on the mortise view (ρ=0.27, p< 0.05), articular displacement on the mortise view (ρ=0.35, p< 0.01), articular displacement on the lateral view (ρ=0.28, p< 0.05), and epiphyseal translation/displacement on the lateral view (ρ=0.55, p< 0.001).

Conclusion: There are several mortise and lateral view radiographic parameters that correlate with increased displacement of transitional ankle fractures on CT. Thus, it is particularly important to evaluate the mortise and lateral radiographs in patients with this injury. Specifically, increased articular displacement on mortise view and lateral view, as well as increased tibiofibular clear space on the mortise view correlate with increased displacement. Increased epiphyseal translation/displacement showed the strongest correlation with CT displacement out of all radiographic measures. These radiographic parameters should be used when determining the need for CT scans in pediatric patients with transitional ankle fractures.