Development and Internal Validation of a Classification System for Predicting Success Rates After Endoscopic Combined Intrarenal Surgery in the Modified Valdivia Position for Large Renal Stones

Objective: To identify preoperative predictors and to develop a classification system for predicting success rate after endoscopic combined intrarenal surgery (ECIRS) in the modified Valdivia position for renal stone treatment.

Patients and methods: We retrospectively analyzed 329 consecutive, single-session ECIRS procedures undertaken in the modified Valdivia position to treat renal stones. The successful status after surgery was determined at 1 month postoperatively using noncontrast computed tomography and was defined as the absence of stones or residual fragments measuring <4 mm. The preoperative factors analyzed included the stone statuses, which were determined by noncontrast computed tomography, and the patients' characteristics. A multivariate logistic regression model with backward selection was used to evaluate the relationships between the preoperative factors and a successful status after ECIRS, and a classification system was developed to predict a stone-free status based on the preoperative factors.

Results: The overall successful outcome rate was 65.3%. Multivariate analysis determined 2 independent predictors of ECIRS outcomes, namely, the stone surface areas (P = .001) and the number of involved calyces (P = .001). These parameters were used to develop the classification system for predicting the successful status after ECIRS.

Conclusion: Stone surface areas and the number of involved calyces independently predicted the successful status after ECIRS. This is the first study to identify the independent predictors and develop a classification table for predicting success rates after ECIRS in the modified Valdivia position.