Objective: To classify intraoperative and postoperative complications using the modified Clavien classification system (MCCS) and modified Satava classification system (SCS) and to evaluate the parameters associated with complications in patients undergoing retrograde intrarenal surgery (RIRS) for renal and proximal ureteral stones. Materials and Methods: We performed a retrospective analysis of 949 patients who underwent RIRS for renal stones and upper ureteral stones at two institutions between March2015 and June2020. Intraoperative complications were assessed using SCC and postoperative complications were graded according to MCCS. Univariate and multivariate analyses were undertaken to determine predictive factors affecting complication rates. Results: The female/male ratio of 949 patients was found to be 346 (36.5)/603(63.5). The median stone size was determined as 13 mm. The stone-free rate was 83.6%after the first intervention, and the final stone-free rate was 94.4% after re-procedure. According to SCS, the intraoperative event and complication incidence was 153(16.1%). MCCS revealed postoperative complications in 121(12.8%) patients. Major complications were observed in 18(1.9%) patients. The rate of complications was higher in patients with renal anomalies (9.9% vs 3.9%, p=0.006). Besides, stone localization, size, number and density were associated with the development of complications (p<0.001, p<0.001, p<0.001 and p=0.002, respectively). In addition, the multivariate analysis revealed that for the patients with grade≥3 complications according to MCCS, only stone-free status was a significant predictor of complication development (p=0.044) whereas for those with grade ≥2b complications according to SCS, significant predictors were stone size (p<0.001), stone density (p=0.022), and fluoroscopy time (p<0.001). Conclusion: This study showed that abnormal kidney anatomy, multiple stones, operative time, and stone-free status were reliable predictors of complication development during and after RIRS. Appropriate preoperative management should be planned according to these predictors to prevent intraoperative and postoperative complications.

Objectives: To externally validate and compare Resorlu-Unsal stone score(RUSS), modified Seoul National University Renal Stone Complexity Score(S-ReSC), Ito’s nomogram and R.I.R.S. scoring systems for predicting capabilities of both the stone-free status and complications in a multi-institutional study. Materials and Methods: We performed a retrospective analysis of 949 patients who were underwent flexible ureterorenoscopy (f-URS) and laser lithotripsy for renal stones in two institutions between March-2015 and June-2020. The RUSS, modified S-ReSC, Ito’s nomogram and R.I.R.S. scores were calculated for each patient by same surgeon on imaging methods. Results were compared for their predictive capability of stone-free status and complications. Results: Of 949 patients 603 were male and 346 were female with a mean age of 47.2±14.3 (range 2-84years). Mean stone burden was 102.6±42.2 (48-270mm2). All nomograms predicted stone-free status (AUC were 0.689, 0.657, 0.303 and 0.690, respectively). All four scoring systems predicted complications with AUC values of 0.689, 0.646, 0.286 and 0.664 for RUSS, modified S-ReSC, Ito’s nomogram, R.I.R.S., respectively. Although all scoring systems were able to predict complications only Ito’s nomogram was able to predict Clavien ≥2 complications. Conclusion: All four scoring systems (RUSS, modified S-ReSC, Ito’s nomogram and R.I.R.S.) could predict stone-free status after f-URS, however the AUC values are not satisfactory in our large patient cohort. Although these scoring systems were not developed for predicting post-operative complications, they were associated with complications in our study. However, these four scoring systems have some significant limitations. The ideal scoring system is yet to be developed.