Flexible ureteroscopy with a flexible and navigable suction ureteral access sheath versus mini‐percutaneous nephrolithotomy for 1–2 cm lower pole renal stones: Protocol for an international, multicentre, randomized non‐inferiority trial (FLAME trial)

Abstract Background Lower pole renal stones measuring 1–2 cm remain challenging to treat. While mini‐percutaneous nephrolithotomy (mini‐PCNL) provides high stone‐free rates (SFRs), it carries tract‐related morbidity. Flexible ureteroscopy (f‐URS) is less invasive but limited in SFR. The flexible and navigable suction ureteral access sheath (FANS) has shown promise in improving stone evacuation and intrarenal pressure control. We hypothesize that FANS f‐URS is non‐inferior to mini‐PCNL for patients with 1–2 cm lower pole stones in SFR. Study Design The FLAME trial is an international, multicentre, randomized, non‐inferiority study directly comparing FANS‐f‐URS with mini‐PCNL in this setting. Endpoints The primary outcome is immediate SFR within 72 hours on low‐dose CT. Secondary outcomes include SFR at 1 month, operative time, postoperative pain, hospital stay, complications (Clavien–Dindo) and quality‐of‐life changes. Patients and Methods A total of 640 adults with CT‐confirmed 1–2 cm lower pole renal stones will be randomized 1:1 to undergo FANS‐f‐URS or mini‐PCNL across 20 high‐volume urology centres worldwide. Randomization is centralized and stratified by site. Radiologists and statisticians will remain blinded to allocation. Sample size was calculated assuming an 85% SFR for both arms, an 8.5% non‐inferiority margin, 80% power and 15% attrition. Analyses will follow both intention‐to‐treat and per‐protocol principles. Trial registration ClinicalTrials.gov NCT07159035.