Evaluation of modified S.T.O.N.E. nephrolithometry scoring system for predicting the one-phase stone-free rate of flexible ureteroscopic lithotripsy

Abstract:

Objective：To modify the S.T.O.N.E. nephrolithometry scoring system for assessing and predicting the stone-free rate（SFR） of flexible ureteroscopic lithotripsy（FURL），and to investigate the predictive value of modified S.T.O.N.E. scoring system for SFR following one-phase FURL. Methods：A literature review was performed to identify clinically relevant and reproducible variables that could affect the SFR of FURL. Five reproducible variables available from preoperative non-contrast computed tomography were measured，including stone burden（S），topography（T），obstruction（O），Number of involved calyces（N），essence of stone（E），which modified the S.T.O.N.E. nephrolithometry scoring system. A retrospective analysis was conducted clinical data of 322 patients with nephrolithiasis undergoing FURL from January 2015 to December 2017. The general conditions，preoperative information，stone characteristics and perioperative variables were collected. The correlation of modified S.T.O.N.E. scores with one-phase SFR，operation time，major complications，hospital stay were analyzed. Receiver operating characteristic（ROC） curves was drawn to detect sensitivity and specificity of modified S.T.O.N.E. scores in predicting the one-phase SFR. Results：The 322 cases’ FURLs were performed suc－cessfully，and the one-phase SFR was 88.2%. The mean modified S.T.O.N.E. score was 6.4（4 to 11） in this cohort. The one-phase SFR was 98.1% in low score（4 to 5） group of 103 cases，91.2% in medium score（6 to 8） group of 182，and 45.9% in high score（9 to 13） group of 37（χ2=74.667，P=0.000）. The modified S.T.O.N.E. score showed significant correlation with SFR following one-phase FURL（OR=5.614，95%CI=1.811 to 13.589，P=0.012），and the area under curve of ROC curves for the modified S.T.O.N.E. score was 0.802（95%CI=0.672 to 0.920），higher than that of each variables in this system. Conclusion：The modified S.T.O.N.E. nephrolithometry scoring system can predict postoperative stone-free status of one-phase FURL. Further research is required to evaluate its performance in external validation.