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

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.

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.

A retrospective comparative study complemented by in vitro simulation experiments.

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 (n = 114) or the control group (n = 126). The experimental group underwent combined Sotn-URS and fURS with basket-assisted stone displacement to the kidney pelvis or upper ureter before laser lithotripsy. The control group underwent conventional in situ lithotripsy using fURS alone. Outcomes, including operative time, SFR (immediate and at 4 weeks), surgeon comfort (Borg scale), first-pass sheath placement success, and complications, were compared.

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%, p < 0.05) and 4-week SFR (91.2% vs 81.7%, p < 0.05), along with shorter total operative time (51.7 vs 70.4 min, p < 0.05) and fURS intrarenal time (22.2 vs 52.2 min, p < 0.05). Surgeon comfort was better (Borg score 0.63 vs 2.9, p < 0.05), and the rate of ureteral mucosal injury was lower (3.5% vs 11.1%, p < 0.05).

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.