Surgical procedure
All patients were placed in the lithotomy position and all operations were performed under the general anesthesia. Among all patients, 421 cases were indwelled F6 double J stent for 2 weeks before FURSL procedure. At first, the double J tubes were removed if the double J tubes were placed, then under the guideline of safety wire, the F9.8 semi-rigid ureteroscope were used to access to ureter. If ureteric calculi were observed, lithotripsy was performed using a Holmium laser with a 365μm fiber at an energy range of 0.8-1.2W and a frequency of 20-25Hz. After confirming the clearance of stone from the ureter, a F12/14 ureter access sheath (UAS) was inserted into the proximal ureter with the guide wire. Then, a F7.5 flexible ureteroscope was passed through the UAS, and the front end of the UAS was placed in the pyeloureteral junction under direct view of the flexible ureteroscope. The perfusion flow was set to 60-100mL/min. When entering the renal pelvis, the renal pelvis and calyces were observed and the stones were found accurately. Lithotripsy was performed using a holmium:yttrium aluminum garnet (Ho:YAG) laser with a 200μm fiber at an energy range of 1.0-2.5W and a frequency of 15-25Hz. According to the actual situation of the operation, three types of lithotripsy were used: fragmentation (high energy, low frequency), dust (low energy, high frequency), and popcorn effect (high energy, high frequency). The stone should be powdered as much as possible (the maximum diameter of the stone is less than 0.4cm), and the larger stone should be taken out with the help of reticular basket for the analysis of stone composition. In order to avoid the damage of flexible ureteroscope, the stones which located at the lower renal calyceal could be put into the middle or upper renal calyceal and renal pelvis through the reticular basket, and then lithotripsy could be carried out. At the end of the operation, all renal calices were checked to confirm satisfied fragmentation before the F6 double J stent was placed routinely.