Clinical impact of stone multiplicity on outcomes of retrograde intra-renal surgery.

OBJECTIVE: To evaluate the impact of stone multiplicity on stone-free rates (SFR), complication rates, and perioperative outcomes following retrograde intra-renal surgery (RIRS) for renal calculi. MATERIALS AND METHODS: A retrospective cohort study on 198 patients who underwent RIRS with holmium laser lithotripsy at a tertiary center from January 2020 to December 2024. Patients were stratified into single-stone (n = 100) and multiple-stone (n = 98) groups. The primary outcome was stone-free status on postoperative imaging. Independent predictors were assessed using Firth's penalized logistic regression to account for low event rates. RESULTS: The overall SFR was 93.0% (184/198), with comparable rates between the single-stone and multiple-stone groups (94.0% vs. 91.8%, p = 0.591). Residual fragments (> 4 mm) were more frequent in the multiple-stone group (8.2% vs. 3.0%, p = 0.132), although this did not reach statistical significance. The overall complication rate was low (4.5%) and comparable between groups (6.0% vs. 3.1%, p = 0.498). On multivariate analysis, stone multiplicity was not an independent predictor of stone-free status (OR 0.521; p = 0.334). CONCLUSIONS: RIRS demonstrates comparable efficacy and safety for single and multiple renal stones, supporting its use on a viable treatment option in patients with stone multiplicity. While statistical significance was not observed, the study was adequately powered (> 80%) only to detect absolute differences of approximately 15% or greater. Therefore, the absence of statistical significance should not be interpreted as evidence of clinical equivalence, and larger adequately powered studies are warranted to determine whether smaller between-group differences exist.