Ureteroscopy including flexible and semirigid ureteroscopy has become the first line choice for upper ureteral stone, and even renal transplant lithiasis [3]. It is safe and cost-effective [4]. Nowadays, both of them have a high stone-clearance rate. With its bendable properties, flexible ureteroscope could reach the majority of calyces [5]. Semirigid ureteroscope makes it in other way. Combining with antiretropulsive devices, it could efficiently prevent stones from migration [6]. Gradually, there is no clear line between the two surgical methods. However, hindered by the higher cost of equipment and maintenance and so on, fURS had not been widely used in many centers. In this paper, we demonstrated that fURS and URS both performed well on stone treatment, and only had slight difference in stone choice.

The SCR of fURS at the one day was significantly lower than that of URS. It was because of that fragment in fURS procedure always in the kidney which was harder to clear. Making good use of the two modes of dusting and fragmentation would help to improve the stone-free rate [7]. Moreover, retrieval tools were also able to remove big fragments. However, it would significantly increase the operation time. In our study, the mean operation time in fURS was 18 min longer than that in URS. Moreover, as the stone size increased, there was so much dust liked debris left, which led to a low SCR. Other procedure like external physical vibration lithecbole might be needed. That was one of the biggest obstacles for the current fURS. As the fragments passed spontaneously, similar SCR was observed at one month. A latest paper suggested that 51.11% of fragments could manage to pass within one month [8].

Since there were few stones escaping from antiretropulsive devices block, it seemed that URS had a higher priority. However, the real was the stones in URS were further away to UPJ. In the stones close to UPJ, fURS was performed more for fear of up-migration. As the same as mentioned by Perez et al., fewer patients with fURS failed treatments or need retreatment [9]. Further analysis in this study revealed that URS was did more susceptible to the stone location. It was consistent with our previous study, which demonstrated that antiretropulsive device was unlikely to be cost-effective for those stones too close to the UPJ [10].

Though significant difference did not occur yet, fURS seemed to be more susceptible to hydronephrosis and stone burden. Lower SCR might be caused by following reasons: (1) High-degree hydronephrosis mainly caused by the large impacted stones. The larger stones would produce the more debris. Then more debris redeposited in the lower renal calyces due to gravity. (2) After relief of obstruction, high-degree hydronephrosis was more likely to cause mucosal bleeding, resulting a poor operative insight. High-degree hydronephrosis also meant expanded renal inner space and abnormal anatomical structure. It resulted in more effort to refind the stone, especially in bleeding environment.

“Ureterostenosis is a kind of rare but severe postoperative complication, with a low success rate of endoscopic management and a high procedural burden that may lead to nephrectomy [11]. ” Several studies tried to find out predictable factors for ureteral stricture formation [12,13,14]. Up till now, we have much conjecture but little evidence about it. Few patients formatted stricture in our two groups. It benefited from ectopic disintegration and proper irrigation. With antiretropulsive device, stones were hauled out while dusting. With flexible ureteroscope, stones were partly disintegrated in the renal space. In other words, committed with prior papers, we demonstrated that Holmium: YAG laser lithotripsy with appropriate irrigation was a safe treatment modality [15, 16]. Impacted ureteric stones are also suspected of carrying a risk of stricture development [17]. Purposely, we collected preoperative hydronephrosis and stone duration. Although it led to bias, it provided important reference information about the duration of obstruction. However, we did not extract any clue. Routine postoperative imaging remains necessary to observe the formation of stricture early after endoscopic treatments [18].

The major limitations of this study were its retrospective design and small sample size. Selective bias potentially existed. We also had no data about the compositions of stones. The number of strictures was small too. Furthermore, we had no stringent standard to judge the hydronephrosis degree. We reduced the bias by letting one to finish all the judgments. Twenty cases of follow-up results were incomplete, and more detailed follow-up results are necessary.