Effectiveness and safety of percutaneous nephrolithotomy with 3D mixed-reality guidance for renal calculi removal

To the Editor: Renal calculi affect 10–15% of adults, and large stones can cause pain and potential kidney damage.[1] Nephrolithotomy is the primary treatment for stones over two centimeters, previously managed by open surgery, which caused significant pain, blood loss, and long hospital stays.[2] Percutaneous nephrolithotomy (PCNL) is a minimally invasive procedure, offering reduced pain, shorter recovery, and fewer complications. However, it requires precise renal puncture and specialized training due to the complex renal anatomy.[3] Holographic imaging is a three-dimensional (3D) visualization technology that uses lasers to capture real-time holograms of the surgical field, providing detailed views. It has shown promise in telesurgery, orthopedics, and neurosurgery.[4,5] Holographic imaging has the potential to enhance the accuracy of PCNL, but it remains unclear whether it offers a significant advantage over traditional PCNL. Therefore, the primary objective of this study was to evaluate the safety and effectiveness of PCNL combined with 3D mixed-reality HoloLens guidance (3D MRHG) for renal calculi removal. Consecutive patients with kidney stones scheduled for PCNL at Beijing Tongren Hospital from January 2020 to February 2023 were enrolled. The inclusion criteria were: (1) kidney stones >2 cm and (2) preoperative enhanced computed tomography (CT) examination of the urinary system. Exclusion criteria were: (1) history of upper urinary tract urothelial cancer; (2) coagulation disorders; (3) age <18 years; and (4) absence of consent to share patient data. The present study was approved by the ethics committee of Beijing Tongren Hospital (No. TRECKY2021-117), and informed consent was obtained from all participants. A high-resolution contrast-enhanced CT scan with 1 mm slice thickness was performed, and CT images in the DICOM format were processed using Mimics 22.0 software (Materialize Corp., Leuven, Belgium) to reconstruct organs and structures [Supplementary Figure 1A, B, https://links.lww.com/CM9/C183]. Furthermore, the planned puncture trajectory was meticulously designed and annotated within the 3D model using 3-matic 13.0 software (Materialize Corp.). This trajectory was carefully navigated through the axis of the targeted renal calyx, circumventing adjacent organs and major blood vessels to ensure an optimal angle for effective stone removal [Supplementary Figure 1C–F, https://links.lww.com/CM9/C183]. The final output of the 3D model was exported in. stl format and converted to. fbx format using open-source Blender 2.8 software (Blender Foundation, Amsterdam, Netherlands). These concerted files were integrated into the head-worn augmented reality devices (HoloLens glasses2; Microsoft, Seattle, WA, USA) for advanced visualization and precision during surgical procedures. The stone burden was assessed using preoperative CT scans to create 3D reconstructed models of the kidney stones. This method allowed for precise measurement of the stones’ volume, providing an accurate reflection of their size. After general anesthesia, the patient was placed in the lithotomy position for perineal disinfection. A supersmooth guide wire was implanted into the ureter using a transurethral cystoscope, and an F5 ureteral catheter was implanted approximately 20 cm along the guide wire. Saline is continuously injected through the ureteral catheter while an indwelling catheter is placed in the bladder. Then, the patient was placed in the same prone position. In the 3D MRHG group, the surgeon wore the HoloLens2 glasses, which projected the 3D holographic image to the surgical field. This enabled the precise adjustment of the 3D model’s size and position based on the human body by utilizing “skin markers” as reference points [Supplementary Figure 2A, https://links.lww.com/CM9/C183]. After adjustment of 3D holographic image, puncture, which was monitored by B-ultrasound, was performed according to the channel and calyx designed during the preoperative simulation puncture [Supplementary Figure 2B, C, https://links.lww.com/CM9/C183]. After successful puncture and placement of the guide wire, a fascial dilator expanded the channel, and an F18 outer sheath was placed. Lithotripsy was guided by a 3D reconstruction, and larger calculi were removed. Post-lithotripsy, a double J tube and nephrostomy tube were placed and fixed. Patients in the control group, selected using the same criteria as the 3D MRHG group, underwent routine PCNL surgery in a prone position with percutaneous renal puncture under real-time ultrasound guidance. The lead surgeon for both the 3D MRGH group and the control group was the same person, having performed more than 50 PCNL surgeries and possessing the title of attending physician. Clinical characteristics and operational data for each patient were documented, including age, sex, side, stone volume, and so on. Intraoperative outcomes included numbers of puncture and channels, surgery time, and bleeding volume. Postoperative outcomes recorded were stone clearance rate, visual analogue scale (VAS), hemoglobin loss, and hospital stay length. Complete stone clearance was defined as no fragments ≥4 mm on postoperative CT, and stone clearance rate was calculated as the percentage of patients who achieve complete stone clearance after treatment. Postoperative blood loss was assessed by calculating the difference in hemoglobin levels between preoperative measurements and those taken on the first day after surgery. Severe complications including organ injury, embolization, and septic shock were recorded. Based on data from previous studies, the surgery time for the 3D MRHG group is 108 min, while the surgery time for the control group is 91 min.[6] With the power set to 0.9 and the significance level set to 0.05, the minimum required sample size per group for this study was calculated using PASS 15.0 (NCSS, LLC, Kaysville, UT, USA) to be 16. Statistical analysis was performed with SPSS version 23.0 (IBM Corp, Armonk, NY, USA). The Shapiro–Wilk test was performed to evaluate the normality of the continuous data. Continuous data comparisons used either the two-independent sample t-test (for normally distributed data) or the Mann–Whitney U test (for non-normal data). The chi-squared test was performed to analyze the differences in categorical variables. Statistically significant difference was set at P <0.05. 3D MRHG was used to facilitate PCNL in 29 patients, and traditional PCNL was performed in 33 patients. The 3D MRHG group comprised 10 females and 19 males with a median age of 57.0 years, while the control group consisted of 10 females and 23 males with a median age of 46.0 years. There were no statistically significant differences in the characteristics between the 3D MRHG group and the control group (P >0.05, Supplementary Table 1, https://links.lww.com/CM9/C183). Holmium laser lithotripsy was used in both groups. Compared to the control group, the 3D MRHG group demonstrated superior accuracy in puncture and instrument navigation, resulting in a significant reduction in the number of punctures (2.0 times vs. 3.0 times, P <0.05), number of puncture channels (2.0 vs. 2.0, P <0.05), surgery time (105.2 ± 9.0 min vs. 125.9 ± 8.3 min, P <0.05), VAS score (6.0 points vs. 7.0 points, P <0.05), and bleeding volume (80.0 mL vs. 110.0 mL, P <0.05, Supplementary Table 2, https://links.lww.com/CM9/C183). There was no significant difference in the stone clearance rate (86.2% [25/29] vs. 78.8% [26/33], P >0.05), hemoglobin loss (8.0 g/L vs. 8.0 g/L, P >0.05), or length of hospital stay (7.0 days vs. 9.0 days, P >0.05) between the two groups [Supplementary Table 2, https://links.lww.com/CM9/C183]. The overall complication rate was significantly lower in the 3D MRHG group than in the control group [Supplementary Table 3, https://links.lww.com/CM9/C183]. According to the Clavien–Dindo classification for postoperative complications, there were three and two instances of Grade I and Grade II complications in the 3D MRHG group, respectively, and each five in the control group experienced the Grade I and Grade II complications, but there were no significant differences between the two groups. Both groups had not reported Grade III to Grade V complications. Significant advancements have been made in the treatment of kidney stones in recent years, with the development of minimally invasive surgical techniques such as PCNL. However, PCNL remains a challenging procedure due to the complex renal anatomy and the need for precise puncture and instrument navigation.[7] To address this issue, computer-assisted surgery systems have been developed, among which the 3D MRHG system is one of the most promising technologies.[8] Porpiglia et al[6] compared the efficiency of 3D mixed-reality endoscopic combined intrarenal surgery (ECIRS) and PNCL under ultrasound guidance for kidney stones. They found that the 3D mixed-reality procedure was effective and was associated with a low intraoperative radiation exposure time.[6] The 3D mixed-reality system has been shown to enhance PCNL by increasing the accuracy of puncture and instrument navigation, reducing the operating time, and improving the overall patient outcomes.[9] The 3D MRHG system offers a more accurate representation of kidney anatomy and stones, allowing surgeons to identify safer and more effective access routes, reducing damage to surrounding organs. Real-time feedback on instrument navigation improves precision, reducing the need for multiple punctures and increasing stone-free rates. Enhanced depth perception from the 3D MRHG system provides a stereoscopic view, improving spatial awareness and instrument targeting. Potential complications specific to PCNL include fever, bleeding, perirenal hematoma, septicemia, and pleurisy. This present comparative analysis indicated a lower complication rate in the group utilizing 3D MRHG, suggesting not only its safety but also its potential in reducing specific surgical risks. This research highlighted that 3D MRHG leads to a decrease in the number of punctures, enhances puncture accuracy, and subsequently lowers the rate of complications associated with the procedure. Such advancements are especially beneficial for doctors at the beginning of their PCNL learning curve, aiding in increasing the success rate of the procedure. Despite its promising potential, there are some challenges and limitations associated with the use of the 3D MRHG system in PCNL. First, the 3D MRHG system requires specialized training for surgeons to become familiar with its use. Second, the cost of purchasing and maintaining 3D MRHG systems may be exorbitant for some hospitals and clinics. Third, alterations in patient positioning can induce slight oscillations of the kidneys within the human body. The 3D MRHG system is incapable of reflecting these minute changes in real-time, which may result in minor inaccuracies in the puncture site. Although 3D MRHG systems have been shown to improve outcomes in PCNL, there is still a need for further research to confirm their long-term benefits and cost effectiveness. Furthermore, the 3D MRHG system is a passive technology in the surgical process, with the surgeon still responsible for decision-making and executing surgical maneuvers. 3D MRHG provides guidance and assistance, but the ultimate success of the procedure depends on the surgeon’s skills and experience. Therefore, it is essential to ensure that surgeons are properly trained and familiar with the 3D MRHG system. The limitation of this study was a single-center retrospective study with a relatively small sample size and short-term follow-up; hence, further multicenter large-sample randomized controlled trials (RCTs) with long-term follow-up are needed to prove the conclusion of the study. Overall, the 3D MRHG system is a promising technological advancement for PCNL. By providing a more accurate and immersive view of the surgical field, the 3D MRHG system can help surgeons puncture effectively and improve patient outcomes. However, further studies are needed to address and confirm the long-term benefits of this technology in PCNL. Funding This study was supported by the Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support (No. XMLX202134 to Hao Ping). Conflicts of interest None.