• 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.