6.3Fr Versus 7.5Fr Mini-Flexible Ureteroscopy for Renal Stones (MINI-FURS)

Renal stone disease is a common condition with an increasing global incidence. Flexible ureteroscopy has become one of the standard treatments for renal stones because it provides excellent stone clearance with a minimally invasive approach. Recent technological advances have led to the development of mini-flexible ureteroscopes with smaller diameters, which may facilitate easier access to the kidney while reducing ureteral trauma and the need for preoperative ureteral stenting.

Although both 6.3Fr and 7.5Fr mini-flexible ureteroscopes are currently available for clinical use, there is limited high-level evidence comparing their clinical performance and cost-effectiveness. This prospective, randomized, single-blinded, non-inferiority trial aims to compare these two ureteroscope sizes in adult patients undergoing flexible ureteroscopy for renal stones.

Eligible participants will be randomized in a 1:1 ratio to undergo flexible ureteroscopy using either a 6.3Fr or a 7.5Fr mini-flexible ureteroscope. All procedures will be performed using standardized surgical techniques by experienced endourologists.

The primary outcomes are stone-free rate at one month after surgery and successful primary renal access without preoperative ureteral stenting. Secondary outcomes include operative time, fluoroscopy utilization, intraoperative ureteral trauma, postoperative ureteral stenting, postoperative pain, complications classified using the Clavien-Dindo system, emergency department visits, hospital length of stay, need for secondary procedures, and cost-effectiveness from the hospital payer perspective.

The investigators hypothesize that the 6.3Fr mini-flexible ureteroscope will improve primary renal access while reducing ureteral trauma, fluoroscopy exposure, postoperative stenting, and overall healthcare costs without compromising stone-free rates. The findings of this study may help establish evidence-based recommendations for selecting mini-flexible ureteroscopes and optimize the surgical management of patients with renal stone disease.

Inclusion criteria

* Adults aged 18 years or older.

• Scheduled to undergo flexible ureteroscopy for renal stones.
• Renal stone size ≤15 mm in the greatest dimension.
• No indwelling ureteral stent at the time of surgery.
• Able and willing to provide written informed consent.

Exclusion criteria

* Active urinary tract infection.

• Anatomical abnormalities of the urinary tract (e.g., ureteral stricture, horseshoe kidney, ectopic kidney).
• Solitary kidney.
• Pregnancy.
• Stones located within a calyceal diverticulum.
• Any condition that, in the opinion of the investigator, would interfere with study participation or follow-up.