Materials and Methods
After receiving the ethics board approval of Amasya University (decision no. 2/25/2021), patients that underwent fURS for the treatment of renal and ureteral stones between January 2017 and January 2020 were retrospectively evaluated. Patients that completed ureteral stone treatment with semi-rigid URS, those with ureteral or renal anomalies or calyceal diverticula, and those with unavailable data were excluded from the study.
All operations were started by entering the ureter through a guide wire (0.035 inch, Microvasive; Boston Scientific Corp., Natick, MA) with semi-rigid URS. Active dilatation was applied with URS. Ureterorenoscopic lithotripsy was performed using fURS (7.5F; Karl Storz Flex-X2, Tutlingen, Germany and Olympus P-5TM, Olympus, Tokyo, Japan) and 270-350 μm Holmium laser (AMS; Sureflex). Ureteral access sheath (12/14 or 14/16 F, Cook Medical, Bloomington, IN or 11/13 or 13/15 F, Boston Scientific, Natick, MA, USA) was utilized to facilitate the removal of stones and reduce intrarenal pressure in both renal and ureteral stones. All operations were performed by experienced surgeons. In all patients, 1.5 F-2.2 F tipless nitinol baskets were used for removal of residual stones. Preoperative D-J placement was applied in cases with treatment-resistant renal colic, pyelonephritis, and a narrow ureter that could prevent access to stone. A postoperative D-J stent or ureteral catheter was placed according to the surgeon’s preference and clinical necessity.  if no clinically significant stones were shown by KUB, uretral catheter was removed at POD 1. D-J stent was removed 2 weeks after the procedure.
The presence of residual stones was investigated using non-contrast computed tomography at the first postoperative month (POM1). SFS was defined as no evidence of stone.
As a result of the retrospective examination, the clinical characteristics of the patients [age, gender, body mass index (BMI), American Society of Anesthesiologists (ASA) score, stone side, ESWL history, preoperative stent requirement, and degree of hydronephrosis], stone characteristics (localization, number, density, and size), and perioperative findings (operation time, length of hospital stay, SFS, and development of complications) were noted. Complications were graded according to the Clavien-Dindo classification. The degree of hydronephrosis was measured according to the Society For Fetal Urology Hydronephrosis Grading System Stone length was measured as the longest diameter and stone width as the shortest diameter in the reconstructed coronal section.17 Stone area was calculated using the formula, length x width x π x 0.25, where π is a mathematical constant equal to 3.14.18 The mean HU measurement was performed in the longest diameter of the stone with bone window and large magnification. The burden and HU value of multiple stones were calculated as described in the original T.O.HO. study.16 The T.O.HO. scoring system does not specify how to grade multi-calyceal stones. Therefore, the stone localization with the highest score was used in the presence of multi-calyceal stones at different localizations.