Factors Associated with Stone-Free Outcomes after Flexible Ureteroscopy for Lower Pole Renal Stones: A Comparative Analysis of Flexible and Navigable Suction and Conventional Ureteral Access Sheaths – AUSET collaboration

Abstract Purpose Flexible and navigable suction ureteral access sheaths (FANS) may alter fragment evacuation and potentially reduce the procedural consequences of unfavorable collecting-system geometry especially lower pole. We evaluated factors impacting postoperative stone-free status between FANS and conventional ureteral access sheaths. Methods This retrospective multicenter cohort included 214 fURS procedures in 176 patients treated at Kaohsiung Medical University Hospital and Seoul National University Hospital. Of these, 107 procedures used FANS and 107 used a conventional sheath. The primary outcome was stone-free status, defined as no residual calculus ≥ 2 mm approximately 1 month after fURS. The main multivariable logistic regression included sheath technique, cumulative stone size, CT attenuation, IW, RIL, IPA, and PSA. Patient-clustered robust standard errors accounted for repeated procedures. Secondary analyses were angle-by-sheath interaction models and a Korea-only analysis assessed effect modification. Results Stone-free status was achieved in 69.2% of FANS procedures and 57.9% of conventional-sheath procedures. In the main adjusted model, larger cumulative stone size was associated with lower stone-free odds (aOR per 1 cm, 0.613; 95% CI, 0.438–0.859; p = 0.004). Higher CT attenuation was also associated with lower odds (aOR per 100 HU, 0.911; 95% CI, 0.849–0.978; p = 0.010). FANS use showed higher adjusted odds (aOR, 1.724; 95% CI, 0.703–4.225; p = 0.234). IW, RIL, IPA, and PSA showed no independent associations. Interaction analyses did not identify sheath-dependent IPA or PSA associations. Conclusion Stone size and CT attenuation were the main independent predictors of stone-free outcomes after flexible ureteroscopy for lower pole renal stones. FANS use was associated with a numerically higher likelihood of stone-free status, although this did not reach statistical significance after adjustment. Anatomical lower pole parameters were not independently predictive in this cohort.