Comparison of Flexible and Navigable Suction Ureteral Access Sheath (FANS) and traditional ureteral access sheath in retrograde intrarenal surgery for renal calculi: a randomized controlled trial

Abstract Background Retrograde intrarenal surgery (RIRS) is an established treatment for renal calculi < 2 cm. Flexible and Navigable Suction Ureteral Access Sheath (FANS-UAS) has been developed to facilitate active evacuation of stone fragments while potentially improving intraoperative irrigation dynamics. This randomized controlled trial compared the efficacy and safety of FANS-UAS with a traditional ureteral access sheath during RIRS. Methods This prospective, single-blind, parallel-group randomized controlled trial was conducted at a tertiary referral centre between February 2025 and April 2026. A total of 161 adults with renal or upper ureteric calculi < 2 cm were randomized to undergo RIRS using either a FANS-UAS ( n = 80) or a traditional ureteral access sheath ( n = 81). Intermittent suction (-150 to -200 mmHg) was applied in the FANS group. The primary outcome was the immediate stone-free rate (SFR) on postoperative day 1 (POD-1), assessed using low-dose non-contrast computed tomography (NCCT). Secondary outcomes included 1-month SFR, operative time, auxiliary procedures, postoperative pain, complications, and duration of hospital stay. Results Baseline demographic and stone characteristics were comparable between the groups. The FANS group achieved a significantly higher immediate SFR than the traditional group (86.3% vs. 37.0%, p < 0.001). At 1 month, SFR was higher in the FANS group (96.3% vs. 88.9%), although the difference was not statistically significant ( p = 0.075). Operative time was longer with FANS (96.3 ± 25.1 vs. 81.2 ± 23.8 min, p < 0.001), while nitinol basket use (10.0% vs. 66.7%, p < 0.001), postoperative pain (VAS 3.2 ± 1.1 vs. 5.1 ± 1.8, p = 0.001), and hospital stay (2.19 ± 0.53 vs. 2.47 ± 0.73 days, p = 0.006) were significantly lower in the FANS group. Clavien-Dindo grade II or higher complications were numerically lower (1.3% vs. 8.6%, p = 0.064). Conclusions Compared with a traditional ureteral access sheath, FANS-UAS significantly improved immediate postoperative stone clearance and was associated with lower postoperative pain and basket utilization, although operative time was longer. Comparable stone-free rates at 1 month suggest that the principal benefit of FANS lies in improving immediate procedural efficacy rather than demonstrating a sustained difference in stone clearance. Further multicentre studies with longer follow-up are warranted. Trial registration Clinical Trials Registry-India, CTRI/2025/10/096605. Registered on 29 October 2025.