External Validation of the Radiographic Investigation of the Distal Extension of Fractures Into the Articular Surface of the Tibia (RIDEFAST Study).

Objective: To test the external validity of the fracture to plafond (FTP-length of fracture/distance to plafond) ratio to rule out distal intra-articular fractures (DIA) in distal tibial shaft fractures at an independent tertiary trauma center.
Design: Retrospective cohort study.
Setting: Two Level 1 trauma centers.
Patients: Two hundred seventeen patients with a distal tibial shaft fracture in the model cohort and 146 patients in the validation cohort.
Intervention: Radiographic measurements to calculate FTP ratio.
Main Outcome Measurements: Calibration plots, area under receiver operating characteristic curve (AUC), and decision curve analyses to evaluate the external validity of FTP ratio to determine DIA.
Results: The AUC for the anteroposterior (AP) FTP ratio was 0.83 [95% confidence interval (CI) 0.78-0.88] in the model data set and 0.86 (95% CI 0.80-0.91) in the validation data set. The AUC for the lateral FTP ratio was 0.82 (95% CI 0.77-0.87) in the model data set and 0.82 (95% CI 0.75-0.88) in the validation data set. The previously established AP FTP cutoff ratio of 0.61 had a 94% negative predictive value in the model cohort and a 100% negative predictive value in the validation cohort.
Conclusion: The FTP ratio is an effective and externally validated screening tool to rule out DIA in distal tibia shaft fractures.
Level of Evidence: Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.
Competing Interests: T. Higgins: DePuy Synthes, OrthoGrid, Summit Medical Ventures, NT nPhase, and Imagen. The remaining authors report no conflict of interest.
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