Efficacy and safety of 6.3-Fr versus 8.6-Fr disposable digital flexible ureteroscopes for pediatric upper urinary tract stones ≤ 2 cm: a randomized controlled trial

Purpose To compare the efficacy and safety of 6.3-Fr versus 8.6-Fr disposable digital flexible ureteroscopes for pediatric upper urinary tract stones ≤ 2 cm. Methods In this prospective randomized controlled trial, children undergoing surgery for upper urinary tract stones at our center between September 2024 and September 2025 were enrolled and randomized (1:1) to the 6.3-Fr or 8.6-Fr group. Preoperative characteristics, operative time, stone-free rate (SFR) at 4 weeks, perioperative complications, number of anesthesia events, and hospitalization-related parameters were collected. The study was registered at ClinicalTrials.gov (NCT06628765). Results Forty children were included, with 20 patients in each group. Baseline demographics and stone characteristics were comparable. The first-attempt ureteroscope insertion success rate was higher in the 6.3-Fr group than in the 8.6-Fr group (60.0% vs. 20.0%, p = 0.010). During second-stage procedures, sheathless retrograde intrarenal surgery (RIRS) was more frequently performed in the 6.3-Fr group (62.5% vs. 12.5%, p = 0.021). Median hospitalization costs were significantly lower in the 6.3-Fr group (13,510 vs. 17,643 CNY, p = 0.001). The number of anesthesia events and the rate of postoperative stent placement also differed significantly between groups ( p < 0.001). Both operative time, length of hospital stay, SFR at 4 weeks, and postoperative complications did not differ significantly ( p > 0.05). Conclusion This study provides the first evidence supporting the efficacy and safety of the 6.3-Fr disposable flexible ureteroscope in children. The smaller-diameter device was associated with higher first-pass insertion success, fewer anesthesia events, and reduced hospitalization costs, offering clear advantages in pediatric RIRS.