Poor clearance of fragments and difficulty accessing lower pole calyces are challenges for the treatment of LPS. It has been reported that the SFR of LPS following ESWL ranges from 25–90%[1–3]. The clearance of fragments of the LPS following ESWL is affected by three spatial anatomical factors, including the infundibulopelvic angle (IPA), infundibular width (IW), and infundibular length (IL). In addition, the measured value of the IPA correlated in a statistically significant manner with the overall success of flexible ureteroscopy for LPS. Berkan et al. evaluated 67 patients with LPS who received retrograde intrarenal surgery (RIRS), and the results showed that the lower pole anatomy, especially IPA, had a significant effect on the SFR of lower pole stones after RIRS. Studies conducted by Jessen et al. showed that IPA and IL have adverse effects on SFR. Stephanie et al. retrospectively reviewed 243 patients with LPS treated with FURS and analyzed the univariate and multivariate influencing factors of SFR. The results showed that the residual stone fragments were negatively related to the more acute IPA and the larger stone diameter.
Koo et al. evaluated the clinical outcomes of reusable FURS compared with those of ESWL in 88 patients, and the results showed that the SFR of FURS was 59.4%, which is similar to the present study. Bozzini et al. prospectively evaluated the efficacy and safety of RIRS, ESWL and PCNL in the treatment of 1 ~ 2 cm-sized LPS. The SFR was 82.1%, and the complication rate was 14.5% after RIRS. Zhang et al. showed that the SFR after FURS was 92%, and the incidence of complications was 8.33% in the treatment of 1–2 cm LPS. Therefore, we found that the SFR after FURS treatment for LPS was similar to the above studies.
The 1-month SFR following a single-use ureteroscope was significantly higher than that after a reusable ureteroscope. The possible explanations are as follows. The single-use FURS used in the study can deflect 275° in the upward and downward directions, and the deflection loss is small when the operating instruments are placed. To a certain extent, it can overcome the lithotripsy difficulty caused by acute IPA. Abdelsehid et al. demonstrated that deflection was impaired when different instruments were placed in the working channels. With 200 µm laser fiber or 365 µm laser fiber, the FURS showed a decrease in deflection by 3.1% ~ 22.7% or 25.9% ~ 46.3%. In the same case, single-use FURS outperformed fiber-optic FURS for all other settings in terms of deflection loss. In addition, the outer diameter of the ZebraScope™ is less than that of URF-V (8.7 Fr vs. 9.9 Fr). Higher irrigation flow and a clearer field of vision brought by a smaller outer diameter are favorable to the enhancement of operative efficiency and effect. Furthermore, the use of single-use products allowed doctors to boldly attempt procedures, without the concern of damage to reusable ureteroscopes with high purchase costs. LPS was one of the significant risk factors for FURS damage, which increased the psychological pressure on doctors.
Based on the present study, we propose the following suggestions for the treatment of LPS using FURS. First, if feasible, the LPS can be moved to the pelvis to lower the complexity barrier of lithotripsy. Second, it is necessary to evaluate the parameters of renal anatomy before surgery, including IPA, IW, and IL. For patients with LPS whose IPA of the involved kidney is acute, FURS with greater deflection should be selected. Third, the stones should be powdered as much as possible during surgery. For larger stone fragments, the nitinol basket should be used to extract or relocate from the lower calyx. In addition, combined with the physical stone removal method, the SFR after lithotripsy can be improved.
This study has several limitations. IPA, IL, and IW were not measured to assess the anatomical data of the target kidney before the operation and further follow-up was not conducted to evaluate the recurrence rates of LPS after FURS treatment. This result requires confirmation in an adequately powered prospective randomized controlled trial in patients with LPS.