SWL is both non-invasive and more practical than URS, and is widely used in clinical treatment of urinary calculi. In studies by Ziaee et al, patients with proximal ureteral stones that were 10 to 15 mm in size underwent three SWL sessions and achieved 78.6% SFR, which were higher than the 72.5% SFR of URS (P༞0.05) . Many shortcomings do however remain for SWL, including the requirement for multiple treatment protocols. Kenneth et al showed that the SFR of initial SWL treatment was 68%, which decreased to 46% after re-treatment 1, and they observed a further decrease in the stone-free rate after re-treatment 2 to 31% (p = 0.001) . SWL and URS are the most commonly used treatment modalities for proximal ureteral stones . And in cases of SWL failure for proximal ureteral stones, complementary URS treatment is a common procedure.
SWL treatment when compared to URS is considered a less invasive treatment option for ureteral stones. However, SWL can cause tissue damage in the kidney, proximal ureter and adjacent organs [13–15]. The mucosal layer of the ureter was damaged by SWL through the increased number of transitional cells during cytological examination of the urine . The inflammatory response of the target tissues was triggered by shock waves through the release of oxidants, prostaglandins, COX-2 and TNF-α leading to tissue damage and edema [14–15]. Information on edema in the urothelial mucosa can lead to the small vessels mucosa becoming more fragile, leading to lower levels of hemorrhage. Edema in the urothelial mucosa also complicates subsequent ureteral URS surgery. Holland et al and Grasso et al also reported that stone fragments can become embedded in the ureteral mucosa after SWL, occasionally becoming completely submucosal and eventually leading to ureteral stricture [16–18]. All these changes may cause more impacted stones. Severs studies have shown the phenomenon that the impacted stone rates are significantly higher after unsuccessful SWL [19–21], which may cause difficulty and even more complications during URS. In our study, we also found that impacted stones and ureteral inflammation edema were seen predominantly in patients having already undergone SWL.
Complications of URS can occur due to many variables. The size of the stones, stone location, and the size of the ureteroscope used are closely related to the occurrence of complications ,. In studies by Kilinc et al  and Tugcu et al , insignificant differences were observed between the complication rates of the two groups. However, only proximal and distal-ureteral small stones were investigated in their studies. In Bora et al study , the mean proximal ureteral stone burden was 83.7 ± 57.2 mm2 and complication rates were significantly higher in patients with previous SWL. The results of this study similarly showed that the complication rates of URS treatment were significantly higher in patients who suffered SWL treatment failure for proximal stones ༞10 mm.
In this study, bleeding and mucosal injury were more likely to happen during URS treatment for patients suffering SWL failure. For improved visibility of the stones, we applied high-pressure saline injections which led to stone/fragment migration to the renal pelvis. To reduce migration, stone baskets were used in both groups. Although a higher number of stone baskets were used in group 1, patient numbers were significantly higher (15.0%) and required flexible ureteroscopes for further treatment to achieve a stone-free status after 2 weeks. Perforation of the ureter is a serious complication during URS procedures , . Alapont et al showed that 68% of their ureteral perforations occurred with stones༞10 mm . Recent research found that the proximal ureter had lower levels of tensile strength which caused ureteral perforation more likely to occur . When stones baskets or balloon dilatation were performed, avulsion and ureteral perforation can occur, particularly in the upper third of the ureter possessing the impacted stones ,. In this study, perforation was more common in those undergoing SWL failure, despite the differences lacking significance. According to our experience, maintaining good visibility represented an effective method to reduce perforation.
Kilinc et al  and Tugcu et al  respectively reported that URS procedures after SWL failure require longer operation times than direct URS for both distal and proximal ureteral stones. Our results were in accordance with these data. When fragmenting stones occurred, the time taken for laser assessments was extended and the need for extra manipulations and the use of auxiliary equipment prolonged the URS procedure.
Fever and hematuria were the most frequent postoperative complications, which were significantly higher in the previously unsuccessful SWL group. We did observe only cases of sepsis in group 1. The occurrence of fevers and sepsis resolved with antibiotic and antipyretic drugs. Further complications in the unsuccessful SWL group may lead to longer hospitalization times.
In previous studies, the success rates of URS with or without unsuccessful SWL were not statistically significant. The success rates of URS sessions after SWL failure ranged from 73.6%-78.9% [19–21]. In their researches, the stones were less than 10 mm in diameter. It was also reported that the success rates (72.5%) of URS were lower for stones rang from 10 to 15 mm . In our studies, after one URS session, the SFR in group 2 was 82.2% which was in accordance with the 82% SFR of primary URS in the proximal ureteral for stones larger than 10 mm . However, group 1 (66.9%) was significantly lower than group 2. To deal with Satava II intra-operative complications, a double J stent was placed and part of these patients required secondary URS treatment. Following the further URS procedure, the SFR of the two groups showed no significant differences (82.5% VS 88.9%). Although there was insignificant difference in SFR, patients who suffered SWL failure were more likely to need multiple URS treatment.
In developing countries such as China, a large number of treatment centers lack available equipment, and many patients prefer SWL due to its low cost. The SFR of re-treating ureteral calculi with SWL significantly decreases after the initial treatment and increases the complication rates of URS after unsuccessful SWL. This remind us the question whether optimal SWL session can be followed by safe URS, regarding the intra-operative complications of URS. Studies in this area are lacking. We calculated the optimal SWL sessions followed by safe URS as 0.5 with a sensitivity of 67.7% and specificity of 71.5%. We further showed that the complication rates of URS were higher in patients who suffered more than a single SWL (72.6% vs 57.4%, p = 0.047). These results suggest that no optimal SWL sessions for safe URS to treat large stones in the proximal ureter currently exist. And patients who underwent more previous SWL were more likely to suffer intra-operative complications during URS complementary treatment. To get lower complications, it was suggested that URS procedures should be delayed 2–3 weeks after unsuccessful SWL .
This study had some limitations, including its retrospective nature that led to selection shifts. Moreover, different surgeons, the small number of patients, unpublished and missing data may have resulted in bias. However, this study was the first to identify whether optimal SWL sessions exist that can be followed by safe URS for proximal ureter stones > 10 mm.