Stone displacement with combined Sotn ureteroscopy and flexible ureteroscopy for lower calyx stones ⩽20 mm: a retrospective comparative study.

Background: The lower calyx is the most common site for kidney stones. While minimally invasive, flexible ureteroscopic lithotripsy often yields suboptimal stone-free rates (SFR) for lower calyx stones due to anatomical constraints and limited endoscope deflection. Objectives: To evaluate the efficacy and safety of a novel technique that combines Sotn ureteroscopy (Sotn-URS) with flexible ureteroscopy (fURS), involving stone displacement before lithotripsy, for managing lower calyx stones ⩽20 mm. Design: A retrospective comparative study complemented by in vitro simulation experiments. Methods: An in vitro model assessed the impact of a 200 µm laser fiber, a 365 µm fiber, a 1.7 Fr stone retrieval basket, and a flexible ureteral sheath on the deflection of a single-use fURS. In all, 240 patients with lower calyx stones (⩽20 mm) were allocated to either the experimental group ( Results: The maximum deflection angle of the fURS alone was 295.7°. Insertion of a 365 µm fiber significantly reduced this angle to 270.1°, while a 200 µm fiber or basket had minimal impact (293.3° and 293.4°, respectively). Compared with control group, the experimental group demonstrated significantly higher immediate SFR (85.1% vs 73.0%, Conclusion: The stone displacement technique utilizing combined Sotn-URS and fURS is an efficient and safe surgical approach for lower calyx stones ⩽20 mm. It uses the stable access and efficient lithotripsy of rigid Sotn-URS and the flexibility of fURS for stone displacement, resulting in improved stone clearance rates, reduced operative time, and lower ureteral injury risk.