Modified UMP techniques

In the modified UMP group, patients were put in the semi-supine combined lithotomy position with operating side elevated at 45° under epidural anesthesia. A 9.5/11.5 F UAS was inserted using the same protocol as the RIRS group. 30–50 ml of saline was injected through the UAS to obtain artificial hydronephrosis. Percutaneous renal puncture was performed under the guidance of ultrasonography. Immediately after that, 10 F and 14 F fascia dilators were used sequentially to establish the tract. After the placement of the 13 F sheath, UMP was performed by holmium laser lithotripsy (1.0–2.0 J, 20–30 Hz). Stone fragments were washed out by an irrigation pump. The UAS was used as an outflow tract for irrigation fluid along with stone fragments. After lithotripsy, ultrasonography was performed again to check for residual stones. The retention of nephrostomy tube was determined according to the removal of stone fragments and bleeding of the tract at the end of surgery. All patients received a 6F JJ stent. The nephrostomy tube was removed between 24 and 48 h after the operation. The operations in both groups were performed by Professor Kewei Xu. The JJ stent was removed around 2–4 weeks in both groups.