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, 13]. Some surgeons believed that either RIRS or PCNL surgery is needed even if the diameter of LPSs is less than 1.0 cm [14]. Endourology surgery is widely used to treat calculi with diameter less than 2.0 cm [15]. The application of RIRS or PCNL 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% [16]. However, flexible ureteroscope still has its own drawbacks, including instrument damage and iatrogenic infection [17, 18, 19]. 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 [20, 21]. In our study, the mean operative time was 95.61 ± 21.9 min, with postoperative fever in four cases and sepsis in one case. 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, while the incidence of complications is high [22]. The most common complications are bleeding and infection. Channel size is the main factor that affect bleeding after PCNL. UMP was first used in 2013 by Desai et al. [7, 8], where they reported 61 patients who underwent lithotripsy using 6 F nephroscopy to insert 11-13 F PCN channels, which resulted in good surgical safety. However, studies have shown that the decrease of PCN channels may lead to (i) the decrease of perfusion efficiency and(ii) incomplete fragmentation of the stones. These drawbacks may result in prolonged operative time and increased intrapelvic pressure, increasing the risk of postoperative infection [23]. Therefore, to date, that the best indication of UMP is kidney stones less than 2.0 cm and its efficiency was equivalent to RIRS [8, 24].
Our research group improved UMP technology in the early stage [9]. Patients were placed in the semi-supine combined lithotomy position and retrograde indwelling the UAS sheath, which improved perfusion 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 needed for UMP was significantly less than RIRS. The SFR of UMP group reached 96.7% which is higher than that of RIRS group while the incidence of surgical complications was similar between the two groups. Compared with the data reported in literature, this improved UMP surgery method has better efficacy and safety than the traditional UMP surgery method. However, our data showed that the decrease of Hb after surgery 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 than that in RIRS group. It indicates that the bleeding risk is high and the postoperative recovery is slow in UMP group.
The most commonly used position for PCNL is the prone position. However, the prone position has some drawbacks, including chest and abdomen compression, longer surgery time due to the position changes of intraoperative, high pressure in the renal pelvis and so on. Therefore, we attempted to improve the postoperative position of PCNL to increase surgical safety and reduce surgical complications. Since 2002, we carried out 45° semisupine position PCNL surgery [25]. Ibarluzea put forward the Galdakao-modified supine Valdivia position (GMSV) in 2007 [26], in the same year that our center was launched. Studies have shown that it has advantages of short operative time, low intrapelvic depression and low risk of colon or pleural injury. The lower calyx is at the forward position, therefore good operating space can be obtained under this position. In addition, PCNL and RIRS can be combined when necessary under this position to improve the surgical efficacy: it is also applicable to complicated cases such as multiple stones and staghorn stones [27, 28].
In terms of postoperative catheterization, we adopted a conservative strategy for the RIRS group. There was no indwelling JJ stent in RIRS group 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 JJ stent and/or 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.
The results indicated that our modified UMP surgery has obvious advantages in the treatment of 1.5-3.5 cm LPSs. However, we are well aware of the small sample size of this retrospective study. Therefore, future prospective studies with larger sample sizes should be carried out to yield more definitive evidence for the usage of the modified UMP in LPSs.