An innovative predictive scoring system for assessing stone-free rate of lower caliceal stones after flexible ureteroscopic lithotripsy: a retrospective cohort study.

BACKGROUND

Lower caliceal stones (LCS) account for 25%-36% of all renal stones. Flexible ureteroscopic lithotripsy (FURL) is first-line treatment for LCS, but its stone-free rate (SFR) is significantly affected by renal anatomy and stone characteristics. Currently, there is a lack of specific, convenient scoring systems for predicting SFR of LCS after FURL.

OBJECTIVES

To assess the factors influencing the SFR of LCS after FURL, and establish a practical, convenient, and accurate scoring system.

DESIGN

A single-center retrospective cohort study.

METHODS

A total of 149 patients who underwent FURL between September 2020 and December 2022 were divided into two groups based on the results of NCCT of the kidney performed 1 month after surgery: Group A (stone clearance group) with 112 patients and Group B (residual stone group) with 37 patients. Variables with p values less than 0.1 from univariate analysis were incorporated into binary unconditional multivariate logistic regression analysis. The degree of correlation was assessed based on the odds ratio of independent risk factors. The optimal cutoff value for the early warning scoring system was determined using the Youden index.

RESULTS

According to binary unconditional multivariate logistic regression analysis, stone length (p = 0.003), stone CT value (p = 0.043), infundibulopelvic angle (IPA; p = 0.031), infundibular width (IW; p = 0.043), calyceal pelvic height (CPH; p = 0.006), and renal pelvis morphology (p = 0.036) were identified as independent risk factors. Each factor was assigned one point based on OR values, resulting in a total score of six points. The area under the ROC curve was 0.859, and the cutoff value was 1.5. Internal validation was performed via bootstrap resampling (1000 iterations). The optimism-corrected AUC was 0.842 (95% CI: 0.797-0.913). When the total score was less than 2, the overall SFR was 96.20%; however, when the total score was ⩾2, this rate significantly decreased to 49.32%.

CONCLUSION

Stone length, stone CT value, renal pelvis shape, IPA, IW, and CPH were identified as independent factors influencing the SFR of LCS after FURL. Each factor was assigned a score of 1, resulting in a prediction scoring system with a total score of six points. A total score exceeding two was associated with a significantly reduced SFR. FURL was strongly recommended for scores of 0-1, used with caution for scores of 2-3, and not routinely recommended for scores 4-6.