PURPOSE: The purpose of this study was to assess the ability of radiographic measures to predict displacement on computed tomography (CT) for transitional ankle fractures. METHODS: This study is a retrospective review of pediatric patients who presented with Tillaux (Salter-Harris III) and triplane (Salter-Harris IV) fractures at a single institution. Radiographs and CT measurements were performed by three independent evaluators. Intraclass correlation coefficients (ICCs) were calculated to determine interrater reliability. Spearman correlations were performed to assess the correlations between each radiographic parameter and CT measurements. RESULTS: A total of 61 patients were included in this study. The average age of patients was 12.3, and 65.6% of patients were male. There was an almost even split of triplane (55.7%) and Tillaux (44.3%) fractures. Overall, measurements showed at least good interobserver agreement (ICC >
0.6). Radiographic anteroposterior view showed the least reliable measurements compared to the 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, CONCLUSIONS: There are several radiographic parameters that significantly correlate with increased displacement of transitional ankle fractures on CT. Increased articular displacement on the mortise and lateral view, as well as increased tibiofibular clear space on the mortise view, correlates with increased displacement. These radiographic parameters may be good indicators for the selective use of CT scans for transitional ankle fractures. LEVEL OF EVIDENCE: Level III, retrospective comparative study.