The treatment of lower pole renal calculi is a difficult point in urology. As the anatomical structure of the lower calyceal is not conducive for stone excretion, ESWL is less effective in the treatment of LPSs [1, 16, 17]. Some surgeons believed that either RIRS or PCNL surgery is needed even if the diameter of LPSs is less than 1.0 cm [18]. Endourology surgery is widely used to treat calculi with diameter less than 2.0 cm [19]. The application of RIRS or UMP in the treatment of calculi larger than 2cm in diameter is rarely reported.
RIRS has developed rapidly in recent years and its indications for the treatment of kidney stones are becoming more extensive. It has been reported that SFR of kidney stones over 2.0 cm treated with RIRS is about 66.7-94.1% [20]. However, flexible ureteroscope still has its own drawbacks, including instrument damage and iatrogenic infection [21, 22, 23]. In this study, disposable and detachable flexible ureteroscope was used to avoid those problems. The lower calyx calculi were moved to the renal pelvis or the upper calyx by a stone basket to facilitate the operation of lithotripsy. However, due to the low efficiency of RIRS, the operation time is linearly correlated with the stone volume, which could lead to the increase in the incidence of postoperative fever and urosepsis [24, 25]. In our study, the mean operative time was 95.61 ± 21.9 min, with postoperative fever in four cases and sepsis in one case. However, none of the four patients with fever after operation had used antipyretics, and their body temperature returned to normal after non-drug treatment. Furthermore, when RIRS was used to treat large renal stones, SFR was low and the possibility of subsequent treatment or staging surgery was increased. In this study, SFR at 1-month after surgery was 84.8%, and SFR at 3-months after surgery was 90.9%, with three patients needed follow-up treatment. Although PCNL has the advantages of high lithotripsy efficiency and freedom from anatomical factors, its complication rate is also higher than RIRS [27]. The most common complications are bleeding and infection. Tract size is the main factor that affect bleeding in PCNL. In order to improve surgical safety, UMP was then invented in 2013 by Desai et al. [9, 10]. They reported 61 cases who underwent lithotripsy using a 6 F nephroscope through a 11-13 F PCN tract, the results showed great efficacy and safety. However, studies have shown that the decrease of PCN tract size may lead to lower perfusion efficiency and incomplete fragmentation of the stones. These drawbacks could result in prolonged operative time and increased intrapelvic pressure, which could higher the risk of postoperative infection [27, 28, 29]. Therefore, to date, that the best indication of UMP is kidney stones less than 2.0 cm and its efficiency seems to be equivalent to RIRS [10, 30].
Our research group has reported a modified UMP technique[11]. Patients were placed in semi-supine combined lithotomy position and a UAS sheath was indwelled, which improved drainage efficiency and reduced intrapelvic pressure. The results indicated that this improved surgical method for the treatment of 2.0-3.0 cm kidney stones had good efficacy and safety. Intraoperative intrapelvic pressure was stable at 5-10 mmHg, lower than the urine reflux threshold (30 mmHg). In this study, we adopted this modified UMP technique to treat 1.5-3.5 cm LPSs. The results showed that the operation time of UMP was significantly less than RIRS. The SFR of UMP group reached 96.7% and the incidence of complications was similar between the two groups. However, our data showed that the decrease of Hb and the incidence of postoperative hematuria in UMP group were higher than that in RIRS group and the postoperative hospitalization time in UMP group was also longer. In conclusion, UMP is more effective than RIRS, along with higher bleeding risk and longer hospital stay. Comparing with the other study by Wilhelm K et al.[14] focusing on UMP and RIRS for 10-35mm renal calculi, our results of UMP showed better efficacy. This may be due to our modified technique. The semi-supine position could avoid position change during the procedure, and the UAS could provide better drainage.
In terms of postoperative catheterization, we adopted a conservative strategy for both groups. There was no indwelling JJ stent in both groups before the operation. Considering that the ureteral injury was relatively large during the operation, JJ stent was routinely indwelling for 2-4 weeks after the operation. The retention of nephrostomy tube was determined according to the intraoperative removal of stone fragments and bleeding in UMP group. The purpose of indwelling nephrostomy tube was to observe the characteristics of drainage fluid. Studies have shown that tubeless can be used in UMP to speed up its postoperative recovery, which warrants further study. During our modified UMP approach, the ureter was manipulated, which made it difficult to perform ‘totally-tubeless’ compared with traditional procedure. This could be a minor drawback in order to reach higher efficacy.