Flexible Ureteroscopy With a Flexible and Navigable Suction Ureteral Access Sheath Versus Mini-Percutaneous Nephrolithotomy for 1-2 cm Lower Pole Kidney Stones

The FLAME Trial (Flexible ureteroscopy for Lower pole stones And Mini-pErcutaneous nephrolithotomy) is an international, multicenter, prospective, randomized, controlled, non-inferiority study that aims to evaluate the safety and efficacy of flexible ureteroscopy assisted by a Flexible and Navigable Suction Ureteral Access Sheath (FANS) compared with mini-percutaneous nephrolithotomy (mini-PCNL) in the treatment of 1-2 cm lower pole renal stones.

This trial will enroll 640 patients from 20 urology centers with substantial experience in endoscopic stone surgery, including hospitals in China, Russia, Turkey, and India. Eligible participants will be randomly assigned in a 1:1 ratio to either the FANS-assisted flexible ureteroscopy group or the mini-PCNL group. All patients will undergo preoperative imaging, intraoperative standardization, and postoperative follow-up according to the study protocol.

The primary endpoint is the stone-free rate (SFR) within 72 hours postoperatively, evaluated by non-contrast-enhanced computed tomography (NCCT). Secondary endpoints include SFR at 1 month, operative time, length of hospital stay, postoperative pain (measured by VAS score), complication rates (graded by Clavien-Dindo classification), changes in renal function, and health-related quality of life (HRQoL).

The FANS, developed to improve irrigation control and active stone fragment suction during flexible ureteroscopy, may provide better visualization, reduce intrarenal pressure, and shorten operative time. By directly comparing FANS-assisted fURS with mini-PCNL, the trial seeks to determine whether a less invasive method can achieve comparable outcomes in terms of stone clearance and complication rates.

Inclusion criteria

• Adults aged 18-75 years;
• American Society of Anesthesiology (ASA) score 1-3;
• Lower pole renal stones-single or multiple-with a maximal diameter of 1-2 cm confirmed by CT;
• Ability to provide written informed consent and adhere to trial requirements.

Exclusion criteria

• Significant urinary tract anatomical anomalies (e.g. horseshoe kidney, ileal conduit);
• Stones located within a calyceal diverticulum;
• History of open nephrolithotomy or ureterolithomy (due to resultant intrarenal anatomical distortion);
• Absolute contraindications to either FANS-f-URS or mini-PCNL, including:

• Uncorrectable coagulopathy;
• Active, uncontrolled urinary tract infection;
• Severe cardiopulmonary disease precluding safe general anesthesia (e.g. decompensated heart failure, refractory COPD);
• Pregnancy;
• Inability to tolerate lithotomy or prone positioning;
• Inability to understand or complete trial documentation.