• Injury · Oct 2020

    Multicenter Study

    Predicting tibia shaft nonunions at initial fixation: An external validation of the Nonunion Risk Determination (NURD) score in the SPRINT trial data.

    • Nathan N O'Hara, Gerard P Slobogean, Kevin O'Halloran, Renan Castillo, Sheila Sprague, Mohit Bhandari, and Robert V O'Toole.
    • Department of Orthopaedics, University of Maryland School of Medicine, 110 South Paca St., Suite 300, Baltimore 21201, MD, USA. Electronic address: nohara@som.umaryland.edu.
    • Injury. 2020 Oct 1; 51 (10): 2302-2308.

    BackgroundPredictive models are common in orthopedic research; however, most models are not validated in an external population. The Nonunion Risk Determination (NURD) score was developed using a single-center cohort of 382 patients to reliably predict tibia shaft nonunions at the time of initial intramedullary nail fixation. The purpose of this study was to externally validate the NURD score using data from the SPRINT Trial.MethodsThe SPRINT trial was a multicenter study comparing reamed versus unreamed intramedullary nails in tibial shaft fracture patients. We assessed the prognostic performance of the NURD score in the SPRINT trial data with comparisons of the c-statistics, calibration plots, and a comparison of predicted probabilities at cut-points defined in the study to derive the NURD score. In addition, we compared the odds ratios of the NURD score components between the derivation (NURD) and external validation (SPRINT) data.ResultsThe NURD score demonstrated significantly worse discrimination in the SPRINT data than was observed in the original data (c-statistic: 0.61 vs. 0.85, p<0.01). The NURD score was well-calibrated in the derivation and SPRINT data. The SPRINT data had less heterogeneity, as determined by the standard deviation of the linear predictors (NURD: 1.4 vs.Sprint0.4). Once we adjusted for case-mix differences, the NURD score had similarly strong discrimination in the SPRINT data (c-statistic: 0.81 vs. 0.85, p = 0.17).DiscussionBased on our external validation, the NURD score lacks generalizability as it underperforms with respect to discrimination in the SPRINT trial data. However, after adjusting for case-mix differences, the performance of the NURD score is comparable between the two datasets, suggesting robust reproducibility.Copyright © 2020. Published by Elsevier Ltd.

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