Comparison of Three Nomograms for Predicting Stone-Free Outcomes after Ureterolithotripsy with Semi-Rigid Ureteroscopy in Distal Ureteral Stones

Abstract

Purpose:

This study aimed to directly compare the Imamura, De Nunzio, and Zhang nomograms for predicting stone-free outcomes following ureterolithotripsy (ULT) with semi-rigid ureteroscopy for distal ureteral stones.

Methods:

A retrospective analysis was conducted on 397 consecutive patients who underwent ULT using semi-rigid ureteroscopy for distal ureteral stones between 2017 and 2024. Stone-free status was defined as the complete absence of residual fragments on postoperative non-contrast computed tomography. The predictive performance of each nomogram was evaluated using receiver operating characteristic curves, with internal validation performed using 1000 bootstrap resamples. Calibration was assessed using calibration-in-the-large, calibration slope, and Brier scores. The clinical utility was examined using decision curve analysis (DCA). Independent predictors of stone-free status were identified using multivariable logistic regression analysis.

Results:

The overall stone-free rate was 90.7%. The independent predictors of non-stone-free status included a stone diameter of ≥10 mm, multiple stones, pyuria, and stone impaction. The Imamura nomogram exhibited the highest discriminative ability (area under the curve [AUC]: 0.853), followed by the De Nunzio (AUC: 0.759) and Zhang (AUC: 0.689) nomograms. The bootstrap AUCs were nearly identical to the apparent AUCs. Additionally, the Imamura nomogram demonstrated the most favorable calibration profiles. DCA indicated that the Imamura nomogram provided the greatest net clinical benefit.

Conclusion:

Among the evaluated nomograms, the Imamura model exhibited superior discrimination, calibration, and clinical utility in predicting stone-free outcomes following ULT with semi-rigid ureteroscopy for distal ureteral stones. Integrating this tool into preoperative assessments may enhance risk stratification and improve individualized patient counseling. Prospective multicenter validation is warranted.