Patients
We recorded the patient sex, age, BMI, stone location, stone size (mm3), and average stone radiodensity preoperatively. Moreover, we evaluated surgical parameters, including total surgical time, ureteroscope usage time, total laser energy, stone-free rate, and use of a basket-wire catheter. Stone-free status was defined as no residual stones or stones smaller than 4 mm in diameter, as determined by plain abdominal radiography three months postoperatively. Patients with a single kidney, urinary diversion, age < 20 years, or medical history of ureteroscopy or ECIRS were excluded from this study.
Study design
The Institutional Review Board of Nagoya City University Hospital approved this ex vivo study before it started (60-19-0044). The study followed the tenets of the Declaration of Helsinki. All patients provided informed consent to participate in the study.
The study design is summarized in Fig. 1. We assessed the performance of 30 WiScope devices (OTU Medical) immediately after use. The scopes were divided into three equal groups: ureteroscopy and ECIRS in the prone and supine positions. Ureteroscopy was performed in patients with proximal ureteral stones < 10 mm and kidney stone < 20 mm in diameter, and ECIRS for patients with larger proximal ureteral stones (> 10 mm) and kidney stones (> 20 mm). Patients with lower pole stone 10-20mm were excluded from this study. The surgical position was randomly determined when treated by ECIRS. The scopes were sent to the laboratory at OTU Medical after use to evaluate their deflection, bending radius, resolution, and water flow rate.
Surgical techniques
All patients were treated under general anesthesia. A 0.035-inch guidewire was inserted through the ureteral orifice followed by a 10/12-Fr or 12/14-Fr ureteral access sheath. In the ureteroscopy group, retrograde fragmentation was performed using a 272-μm holmium YAG laser (Cyber Ho, Quanta System, Milan, Italy), and the fragments were removed using a basket wire catheter (NCircle, Cook Medical, Bloomington, IN, USA). In the ECIRS groups, percutaneous access was established using a 16/17.5-Fr miniature percutaneous nephrolithotomy tract (Karl Storz, Tuttlingen, Germany). Two urologists simultaneously fragmented the stones, one by antegrade fragmentation using LithoClast lithotripsy (Electro Medical Systems S.A., Nyon, Switzerland) with a 12-Fr mini-nephroscope (Karl Storz), and the other by retrograde fragmentation using a holmium YAG laser with fURS. The fragments were washed through the nephrostomy sheath using retrograde irrigation.
Postoperative scope microdamage evaluation
The scope deflection, bending radius, resolution, and water flow rate were assessed to determine whether the postoperative status exceeded the pass criteria before shipping, as shown in Supplementary Table S1–S3. The status of each scope was evaluated as follows:
Deflection
- The deflection section was bent to its utmost up and down positions by pushing the articulation level of the scope without any accessories in the working channel.
- The angle was measured using a digital protractor.
Bending radius
- The deflection section was bent to its utmost up and down positions by pushing the articulation level of the scope without any accessories in the working channel.
- The radius was measured using a digital caliper.
Water flow rate
- One end of the tube was inserted into a 500-mL normal saline bottle, and the other end was connected to an irrigation port of the scope. The accessory port was sealed with a cap.
- The 500-mL normal saline bottle was hanged vertically 100 cm above the scope.
- The scope was held in a horizontal position, and the valve opened.
- The amount of water flowing in one minute was measured.
Resolution
- A 1951 U.S. Air Force (USAF) resolution test chart (Fig. 1) was placed underneath the distal tip and parallel to it.
- The distance between the tip and target was adjusted to 10 mm with a vernier caliper and distortion was checked using distortion grid target cards.
- The resolution was recorded in line pairs per millimeter (LP/mm) and determined using a reference chart included in the test target.
Statistical analysis
Data are presented as numbers (%) or medians (interquartile ranges) and analyzed using EZR for R (R project 3.6.3)[11]. Fisher’s exact test and Mann-Whitney U test were used to compare the ureteroscopy and ECIRS groups. The Kruskal-Wallis test was used to compare the three groups. Moreover, logistic regression analysis was performed to investigate the association between the overall scope damage (deflection, bending radius, resolution, and water flow rate) and other variables such as stone size, total laser energy, surgical position, and the use of a basket wire catheter. Statistical significance was set at P < 0.05.