Factors predicting stone-free rates after retrograde intrarenal surgery for lower pole kidney stones

Abstract

Introduction: We aimed to investigate the factors impacting stone clearance following retrograde intrarenal surgery (RIRS) for lower pole kidney stones and to determine whether there is a significant relationship between the infundibular pelvic angle (IPA) of the kidney's lower pole and stone fragment clearance. Methods: We retrospectively reviewed patients who underwent flexible ureteroscopy (f-URS) for lower pole renal calculi between December 2020 and July 2023 at our institution. Patient demographics and stone parameters were recorded, including stone size, number, volume, density, and IPA. Intraoperative data, including total operative time, lasing time, type of laser used, and stone composition, were collected and analyzed. All patients underwent a computed tomography (CT) scan at three months followup. We recorded the presence of residual stones and the percentage of stone volume reduction. Patients with a stone size 3 mm were deemed stone-free. All patients were discharged home on the same operative day. Results: A total of 123 patients were included in the study: 71 in the stone-free group (group 1) and 52 in the residual stones group (group 2). On univariate analysis, there were significant differences between the two groups in terms of stone size, IPA, and the type of ureteroscopy used. At three months followup, 96% (24/25) of patients with an IPA <30° had residual stones, compared to 28.6% (28/98) of patients with an IPA >30° (p<0.001). There was no significant difference in the intraoperative or postoperative complications between the two groups. On multivariate analysis, IPA and stone size were the only predictive factors for the presence of residual stones. Twelve patients (23.1%) from group 2 required retreatment. Conclusions: RIRS is an effective treatment option for the management of lower pole kidney stones. IPA, in conjunction with stone size, appears to dictate the stone clearance rates of RIRS for lower pole stones.