The effect of stone size on the success of fluoroscopy-free retrograde intrarenal surgery

Abstract Background Fluoroscopy is routinely used during retrograde intrarenal surgery (RIRS) but exposes both patients and operating room staff to ionizing radiation. Fluoroscopy-free RIRS has emerged as an alternative strategy; however, the influence of stone size on surgical success remains insufficiently defined. Methods This retrospective study included 224 patients who underwent fluoroscopy-free RIRS between January 2021 and January 2023. Patients were stratified according to stone size as < 15 mm (Group 1, n = 65) and ≥ 15 mm (Group 2, n = 159). Demographic and stone-related variables were compared between groups. Surgical success was defined as complete stone clearance or clinically insignificant residual fragments < 3 mm on postoperative computed tomography. Multivariable logistic regression analysis was performed to identify independent predictors of surgical success. Results The median age was comparable between the two groups ( p = 0.770). No significant differences were observed regarding sex, stone location, or stone density. Median stone size was 8 mm (range, 4–14 mm) in Group 1 and 18 mm (range, 15–27 mm) in Group 2 ( p < 0.001). Overall surgical success was 72.3%, with a significantly higher success rate in Group 1 than in Group 2 (96.9% vs. 62.2%, p < 0.001). Multivariable logistic regression analysis demonstrated that stone size ≥ 15 mm was independently associated with a lower likelihood of surgical success (OR 0.039, 95% CI 0.009–0.167, p < 0.001), while higher stone density was also independently associated with reduced surgical success (OR 0.999, 95% CI 0.998–1.000, p = 0.021). Among the 62 patients with surgical failure, 13 (21.0%) underwent repeat RIRS, 25 (40.3%) received extracorporeal shock wave lithotripsy, and 24 (38.7%) were lost to follow-up. Conclusion Fluoroscopy-free RIRS is an effective treatment option for selected patients, particularly those with stones < 15 mm. Stone size is an independent predictor of surgical success and may serve as a practical preoperative criterion for patient selection when considering a fluoroscopy-free approach.