To evaluate the risk of repeat surgery and stone-related events after flexible ureteroscopy (fURS) for renal stones, and to identify their predictive factors.

This was a single-center, retrospective cohort study of patients (n = 664) who underwent fURS for renal stones with or without concomitant ureteral stones between January 2012 and December 2019. The primary outcomes were time to ipsilateral stone-related surgical intervention and any stone-related event (including ipsilateral renal colic, symptomatic ureteral calculi, obstructive urinary tract infection, and surgical intervention).

During median follow-up of 31.1 months, 103 (15.5%) and 135 (20.3%) patients experienced surgical intervention and any stone-related event, respectively. The estimated 2-year intervention-free survival and stone-event-free survival was 86.9% and 81.6%, respectively. On Cox multivariate analysis, younger age (hazard ratio [HR] 0.96), history of stone surgery (HR 2.17), larger preoperative stone burden (HR 1.03), and larger residual fragment (HR 1.09) showed an association with future intervention. Use of the four identified risk factors (age ≤60, history of stone surgery, stone burden ≥20 mm, and residual fragment ≥4 mm) allowed stratification of patients based on the risk of future intervention (low [score: 0-1], intermediate [2], and high [3-4] risk). The estimated 2-year intervention-free survival rates in low-, intermediate-, and high-risk groups were 96.2%, 86.4%, and 71.3%, respectively.

Patients undergoing fURS are at risk of future ipsilateral surgical intervention and stone-related events. Our simple predictive tool can facilitate treatment decision-making by identifying patients who are at high risk of recurrence.