Relapse Following Ultrasonic Propulsion-Facilitated Clearance of Residual Kidney Stone Fragments Versus Observation

Background: In patients with residual kidney stone fragments after treatment, ultrasonic propulsion (UP) reduced risk of relapse by 70% over 5 years compared with untreated controls. This study presents a second, independent trial of UP to reduce relapse of stone-related events at 1 year follow-up. Materials and Methods: In this multicenter, open-label, randomized, controlled trial, 24 adults with residual fragments ≤5 mm at least 4 weeks after operation an for kidney stones were enrolled. Using block randomization (4), participants were randomized to treatment (n = 12) with UP or observation (n = 12). The primary outcome was relapse, defined as a symptomatic stone event necessitating medical attention or operation within 1 year of enrollment. The cumulative incidence of relapse was estimated using the Kaplan-Meier method. Log-rank test was used to compare the treatment (UP) and control (observation) groups. Results: The trial was conducted from April 2024 to June 2025. Fragments remained a median of 6 months after procedure before study enrollment. Median (interquartile range) follow-up was 358 (342-365) days. There were no relapse events in the treatment group, whereas 50% of the control group had a relapse event (6/12, p < 0.005). The restricted mean time-to-relapse in the control group was 105 ± 48 days. Conclusions: Removal of residual stone fragments by UP reduced relapse of symptomatic stone events and need for operation in the year after intervention, compared with observation.