External Comparison of Recent Predictive Nomograms for Stone-Free Rate Using Retrograde Flexible Ureteroscopy with Laser Lithotripsy

Abstract

Objective:

To assess and compare the applicability of the Resorlu-Unsal Stone Score (RUSS) and the Modified Seoul National University Renal Stone Complexity (S-ReSC) score for flexible ureterorenoscopy (f-URS).

Patients and Methods:

We retrospectively analyzed the hospital files of 719 patients who had been treated with f-URS for kidney stone at two referral centers between July 2012 and December 2015. The RUSS and Modified S-ReSC scores were calculated by the same surgeon for each patient by using imaging methods and were compared as to their predictive capability for postoperative success.

Results:

A total of 339 patients (168 men and 171 women) with a mean age of 46.5 ± 16.1 (range:1–86) years and a mean body mass index of 27.1 ± 4.1 (range: 12.8–38.5) were included in the study. The mean stone size was 14.4 ± 5.4 (4–40) mm, and the mean stone surface area was 145.3 ± 76.8 (20–658) mm². The overall stone-free rate was 70.1%. The mean scores were 0.5 ± 0.7 and 1.8 ± 1.1 for the RUSS and Modified S-ReSC, respectively. In the logistic regression analysis, musculoskeletal deformity, stone size, and the RUSS were identified as independent predictive factors affecting stone-free status (p: 0, p: 0.014, p: 0.048, respectively). Among these parameters, the RUSS had the highest predictive capability (area under curve value 0.65, [95% confidence interval 589, 721]).

Conclusions:

Stone size, presence of musculoskeletal abnormalities, and the RUSS score are important factors affecting SF status after f-URS. Despite the RUSS being an independent predictive factor for SF status, more comprehensive systems with higher predictive capability are needed for clinical usage and academic reporting.