Stone-event-free survival after ureteroscopic lithotripsy according to residual fragment size: Zero residual fragment indicates a good prognosis

The aim of this study was to evaluate stone event-free survival after ureteroscopic lithotripsy (URSL) according to the size of residual renal stone fragments. We retrospectively collected data from all patients who underwent URSL at our institution from 2008 to 2021. A total of 1334 cases were included and divided into 0 mm (1030 cases), < 4 mm (214 cases), and ≥ 4 mm (90 cases) groups. Patient characteristics, surgical outcomes, and postoperative stone events were evaluated. Stone event-free survival rates were compared between the groups. A total of 214 (16.0%) patients developed stone events during the mean follow-up period of 763 days. The number of stone events in the 0 mm, < 4 mm, and ≥ 4 mm groups were 102 (9.9%), 57 (26.6%), and 55 (61.1%), respectively. Regarding the stone-event-free rate, the 1-year rates in each group were 95.8%, 86.9%, and 44.9%, respectively, and the 5-year rates were 81.8%, 51.6%, and 28.0%, respectively. Regarding the reintervention-free rate, the 1-year rates in each group were 97.4%, 91.7%, and 50.5%, respectively, and the 5-year rates in each group were 86.3%, 61.6%, and 35.5%, respectively. The log-rank test showed a significant difference in the stone-event-free and reintervention-free rates in each group ( p  < 0.001). In conclusion, both stone-event-free and reintervention-free survival after URSL differed according to residual fragment size. A zero residual fragment indicated a better prognosis than other residual fragment sizes.