Urolithiasis is one of the most common diseases in urology, which has a high incidence in the world. Its incidence rate varies, among which North America has the highest incidence rate of 7–13%, Europe has the highest incidence rate of 5–9%, and Asia has a relatively low incidence rate of 1–5% (1). Kidney stones can lead to renal colic, urinary tract infection, and obstruction and are also risk factors for chronic kidney disease (2). The treatment of upper urinary calculi has always been the focal point of medical research. Surgical treatment was the main treatment method of the upper urinary tract stone. Open surgery was highly traumatic and could only be used for some special patients. Percutaneous nephrolithotomy has the highest rate of surgical exclusion for large stones and multiple kidney stones. Tubeless minimally invasive percutaneous nephrolithotomy may be a probable choice for strictly chosen patients (3). The flexible ureteroscopes (f-URSs) were taking an essential role in recent years and the new thulium laser system during ureteroscope was giving interesting results (4).

In the recent revision of the European guidelines on the management of urolithiasis, ureteroscope was recommended as a first-line management option, especially for stones measuring between 10 and 20 mm. Moreover, for stones > 1.5 cm in the lower pole, a flexible ureteroscope is also one of the recommendations (5).

However, the existing limitations on reusable flexible ureteroscope (ru-fURS) include a high initial purchase cost, high expenditures for repair, and a risk of cross-infection (6). Studies have shown that even when ru-fURS was cleaned manually and disinfected by hydrogen peroxide gas, contamination could still be found (7, 8). For solving these problems with existing ru-fURS, a single-use flexible ureteroscope (su-fURS) has been proposed and has recently come to gain achievements (9, 10).

In fact, for su-fURS, there is still a lack of high-level evidence to compare its safety and efficiency with that of ru-fURS. Therefore, the purpose of this meta-analysis is to compare the clinical efficacy and safety of the treatment of the patients with upper urinary calculi between the two types of scopes.

The f-URS has been used in the field of urology for more than 40 years and the development of f-URS is perfectly in accordance with the concept of urology in the field of minimally invasive surgery. In recent decades, the studies reported on f-URS have increased (23). A meta-analysis has shown that, compared with extracorporeal shock wave lithotripsy (ESWL), f-URS could successfully treat the patients with stones <2 cm, with a higher SFR, especially 1–2 cm in the lower pole (24).

However, the limitations in conventional f-URS, i.e., ru-fURS, contain a high initial purchase cost, expensive repair, a risk of cross-infection, and durability at a later stage. To overcome some limitations of ru-fURS, the conception of su-fURS has been proposed (25). It is, particularly, important to discuss the difference between the su-fURS and ru-fURS. As far as we know, this is the first meta-analysis to explore the differences between the two f-URS that aimed to provide medical evidence for clinicians to choose the appropriate approach.

After a sensitivity analysis (Figure 3), this meta-analysis of OT was eventually included in six studies. The final result indicated that no significant differences exist between the two f-URS. It could be seen that the OT of su-fURS procedure was more than ru-fURS in Ding et al. study (16). Professor Ding et al. used a kind of su-fURS, which was named Polyscope and developed in 2011. The surgeon adjusted the degree of deflection of the Polyscope by the force to squeeze the handle constantly and become fatigued during prolonged operation, especially for stones in the lower calyces (16). In addition, the Polyscope lacked two-way deflection, which could not only increase the difficulty in operation but also cause, sometimes, loss of navigation control (26). These causes all bring out increased OT of su-fURS. On the contrary, Salvado et al. reported the use of su-fURS that was the Uscope (PU3022), which was developed in 2017. It has a special self-locking technology that could reduce the fatigue of the surgeon (27). We speculate that the difference between su-fURS themselves was the main reason. Different definitions of time and technical proficiency of the surgeon are also important factors affecting the time of OT.

In terms of EBL, LOS, and SFR, our meta-analysis showed that no significant statistical difference. Since the introduction of su-fURS, it has undergone an evaluation of a series of in vitro experiments. Several studies have indicated that there were no remarkable differences in image quality and deflection ability between the su-fURS and ru-fURS (28, 29). Different stone locations, calyceal structures, long learning curves, and surgeon proficiency are all probable reasons.

The previous study (30), which compared the su-fURS and ru-fURS for the renal stones, was different from our study results, especially in terms of OT and SFR. Sometimes, the SDs are not presented in the article and researchers need to estimate SDs from other related information such as standard errors, confidence intervals, p-values, and t-values. Different calculation methods may be the reasons. In addition, the sensitivity analysis results of their study are not stable, which means that results were greatly affected by bias and should be very careful when concluding results.

Our final meta-analysis results about complications and demonstrates that no statistical difference exists between the su-fURS and ru-fURS. In addition, we did subgroup analysis according to the Clavien–Dindo grades, and the statistical difference can only be found in the Clavien–Dindo grade II (OR 0.47; 95% CI 0.23–0.98; p = 0.04; Table 2). According to the existing studies, most complications were grade I–III (98%) and the most common complication in grade II is urinary tract infection (31). Studies have shown that even when ru-fURS was cleaned manually and disinfected by hydrogen peroxide gas, contamination could still be found (7, 8). This may lead to cross-infection between the patients (32). The amount of cleaning and disinfection could also affect the service life of the extremely fragile equipment. On the other hand, the su-fURS automatically eliminates the risk of contamination (25). However, many factors could affect the occurrence of postoperative infections and the definition of urinary tract infection also was the influencing factor. Generally speaking, the outcome needs to be with respect to caution.

The greatest advantage of su-fURS is its cost-effectiveness, which means lower price, no maintenance, and is ready to use. Professor Martin et al. reported a 12-month demographic-based cost-effectiveness analysis in the United States pointing out that the su-fURS and ru-fURS reached the financial breakeven point in 99 cases (33). Another study showed that if the price of su-fURS is no higher than $1,200, it would be more economical (9). One study, which included 23 cases (14 cases for URF-P6, nine cases for LithoVue) and was a small sample cost analysis, showed that compared with URF-P6, LithoVue acquisition costs were higher, but savings were achieved in the terms of labor, consumables, and repair. When these factors were taken into account, the total cost of using these two fURS per case was comparable (34). Nevertheless, these studies not only contain the treatment of the upper urinary stones, but also diagnostic and biopsy. The aforementioned research conclusions need to be with respect to caution.

We followed the PRISMA guidelines strictly to perform this meta-analysis (35). However, some limitations cannot be avoided. First, the studies included were not all high-quality RCTs, leading to insufficient levels of evidence. Second, a limited number of clinical studies, so it is not convincing to apply it on a large scale. Third, lacking detailed date, we fail to perform a subgroup analysis of stone location and stone size. Fourth, due to the definition of expenditure and income, we failed to perform a meta-analysis on cost-effectiveness. This was an important inherent limitation of our study.

In conclusion, our meta-analysis demonstrates that su-fURS, compared with ru-fURS, has similar effectiveness and better security for patients with upper urinary calculi which provides some benefit to medical institutions of less surgical volume. A larger sample size, multicenter, and longer follow-up RCTs are still needed to support our conclusion.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author/s.

YL conceived and designed the experiments. LP and JinzL analyzed the data. JinzL, JinmL, and JW contributed to reagents, materials, and analysis. CM and LP wrote the manuscript. All authors have read and approved the final manuscript.

This study was supported by the Promotion Project of Health Suitable Technology of Sichuan Province (18SYJS15) and the Health Commission of Sichuan Province(20PJ305).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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