External Validation of the Radiographic Investigation of the Distal Extension of Fractures Into the Articular Surface...

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.

Retrospective cohort study.

Two Level 1 trauma centers.

Two hundred seventeen patients with a distal tibial shaft fracture in the model cohort and 146 patients in the validation cohort.

Radiographic measurements to calculate FTP ratio.

Calibration plots, area under receiver operating characteristic curve (AUC), and decision curve analyses to evaluate the external validity of FTP ratio to determine DIA.

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.

The FTP ratio is an effective and externally validated screening tool to rule out DIA in distal tibia shaft fractures.

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.