Optimizing the Scope–Sheath Compatibility in RIRS: Matching of Reusable and Single-Use Flexible Ureteroscopes with FANS

Background/Objectives: Adoption of single-use ureteroscopes (SU) and flexible and navigable suction ureteral access sheaths (FANS) have improved flexible ureteroscopy (fURS) efficiency and safety. However, the impact of scope–sheath pairing is less studied. This study aims to compare four scope–sheath configurations using reusable ureteroscopes (RU) and SU with either 11/13Fr or 12/14Fr FANS. Methods: We retrospectively evaluated 184 patients undergoing fURS for kidney solitary stones of 10–25 mm. Patients were manually matched across four groups: RU-11/13FANS, RU-12/14FANS, SU-11/13FANS, and SU-12/14FANS (46 patients in each). The endpoints were 30-day stone-free rate (SFR), operative time, surgeon-reported visibility (image clarity and procedural continuity) and postoperative complications. Results: Operative time was significantly shorter in single-use scope groups (p < 0.001). Visibility scores were highest in SU-12/14FANS and lowest in RU-11/13FANS across all subdomains. SFR was higher in SU groups. SU-11/13FANS had a significantly higher SFR than RU-12/14FANS (p = 0.027). In the reusable group, the use of 12/14Fr FANS was associated with a lower SFR compared to the 11/13Fr configuration. Complication rates were low (8.2% overall) and comparable among groups. Conclusions: Pairing SU with 12/14Fr FANS provided optimal visibility and good stone clearance without increasing complications. In contrast, RU paired with 12/14Fr FANS showed slightly reduced efficacy, possibly due to impaired maneuverability. The scope–sheath interaction influenced outcomes differently across scope types, underlining the importance of their matching in fURS.