Efficacy and Safety of Tip-Flexible Suctioning Ureteral Access in Renal Stone Treatment

Introduction

Percutaneous nephrolithotomy (PCNL) and flexible ureteroscopic lithotripsy (FURS) are the 2 primary surgical intervention techniques used for kidney stones, a condition affecting approximately 1 in 8 adults in the United States during their lifetime, with an annual incidence exceeding 600 000 new cases. This epidemic imposes annual healthcare costs surpassing $10 billion in the United States alone, including 4.8 billion in direct medical expenditures and $5.3 billion in lost productivity [1,2]. Use of flexible ureteroscopic lithotripsy is becoming more and more common due to its minimal surgical wound, low risk of surgical complications, and shorter recovery time. Importantly, patient-centered factors such as preoperative anxiety – a critical determinant of postoperative satisfaction – can be mitigated through interventions like video-based education, further enhancing the appeal of FURS as a patient-friendly approach [3]. However, the application of this technology is limited because flexible ureteroscopic lithotripsy has a relatively low efficacy for heavy-load renal calculi, and long-duration endoscopic surgery can easily cause high pressure in the renal pelvis, which can then lead to serious complications like fluid extravasation, urogenic sepsis, and even renal rupture [4]. Percutaneous nephron lithotomy (PCNL) is one of the primary surgical procedures currently used for clinical management of urinary calculi larger than 1 cm. This surgical technique can be used to remove stones of various sizes and characteristics, but it requires creating a large operation channel during the procedure, which increases the risk of secondary trauma to the urinary tract and renal parenchyma [5–7]. Advances in minimally invasive techniques, such as the novel flexible negative-pressure suction ureteral sheath combined with FURS, aim to address these limitations by improving stone clearance efficacy and reducing intraoperative risks. These innovations are particularly urgent given the growing economic burden of nephrolithiasis, which often causes significant out-of-pocket costs and financial stress for patients, even with insurance coverage [2]. Recent advancements in robot-assisted surgery have introduced robotic pyelolithotomy as a viable alternative, particularly for complex stone burdens. A 2024 multicenter study reported an 89% stone-free rate with robotic approaches, comparable to PCNL, while demonstrating 30% reduced blood loss and 1.5-day shorter hospitalization compared to conventional techniques [8].

This study investigated the clinical efficacy and safety of FURS with a flexible suction sheath for renal calculi measuring 2–3.5 cm, comparing outcomes to PCNL and evaluating its potential to bridge existing gaps in stone management.

Material and Methods

PATIENTS:

This retrospective study enrolled 430 patients diagnosed with unilateral renal calculi who underwent surgery at the First Affiliated Hospital of Huzhou Normal College between March 2021 and January 2024. This study was approved by the Institutional Review Board Committee of the First Affiliated Hospital of Huzhou Normal College (Ethics Committee approval no. 2024KYLL035-01). Patient composition, case numbers, and exclusion criteria are presented in Figure 1. All experimental protocols involving humans were performed in accordance with institutional guidelines and the Declaration of Helsinki.

Patient consent for publication: Not applicable.

Criteria for inclusion were: (1) age greater than 18 years; (2) diagnosis of stones above the ureteropelvic junction by ultrasound, urography, and CT; (3) unilateral treatment; (4) stone diameter was 2–3.5 cm; (5) signed the surgical consent form and opted for voluntary surgical stone treatment; (6) this was the first time the patient had undergone surgery and no prior history of urinary stone surgery existed. The exclusion criteria were: (1) coagulation disorders; (2) dysfunction of the heart, lungs, kidneys, and other major organs; (3) urologic tumors; (4) severe ureteral stricture or malformation that precludes safe insertion of the UAS; (5) severe infection prior to surgery; (6) mental and cognitive disorders; and (7) pregnant or lactating. Every patient gave their informed consent for the research.

Prior to surgery, all patients underwent urinary ultrasonography and/or abdominal non-contrast computed tomography (CT). Before the procedure, we informed the patients about the stone, and with their permission, the surgical plan was carried out. The study’s participants had no prior history of coagulation issues or renal tumors. When necessary, computed tomographic urography (CTU) was advised to rule out intrapelvic tumors, particularly in patients with normal renal function. Usually, after a multidisciplinary consultation with 2 board-certified physicians, the decision was made to treat with PCNL or the NFTS-UAS regimen based on the type of renal stone and patient selection.

The largest stone diameter on non-contrast CT was used to calculate the stone burden for each patient; in cases with multiple stones, the longest axes of the stones were added together to determine the stone burden. Laboratory testing and urine cultures were part of the preoperative evaluation. According to the patients’ positive urine culture results, appropriate antibiotic prophylaxis was given both before and during surgery. Urine microscopy and urine culture also verified that urinary tract infections were sufficiently under control prior to surgery. Preoperative and intraoperative prophylactic quinolone or cephalosporin antibiotics were administered to patients whose urine cultures came back negative. Three skilled surgeons performed all PCNL and FURS procedures.

SURGICAL TECHNIQUE:

Group 1 patients were treated using a novel flexible-tip suctioning ureteral access sheath combined with flexible ureteroscope (Ureteral access sheath: GRIT GM-UAS-B-12-450/350; Flexible ureteroscope: KARL STORZ 11278VS Spies Video Flex-VC). The main components of this innovative ureteroscope sheath are a flexible head and a “Y” tail that can be attached to a vacuum device (Figure 2). The UAS’s back end has a connection channel that is linked to the vacuum device to create a suction effect. To allow the ureteroscope to enter the UAS, a detachable perforated elastic rubber membrane is designed at the UAS’s tail. Suction efficiency can be increased by sealing the rubber following the FURS procedure. The UAS’s rear air hole functions as a wind door, and surgeons can use their fingers to press to change the suction system’s negative pressure (Figure 3). The stable maintenance of negative pressure in the NFTS-UAS system is achieved through a combination of its unique design features (flexible tip, suctioning channel with venting slit) and the surgeon’s ability to actively control the vacuum device settings. This dynamic system allows for continuous irrigation and suction, ensuring effective stone removal and maintaining a stable negative pressure throughout the procedure. The patient undergoes surgery under general anesthesia, is placed in a lithotomy position, has unilateral kidney stones treated, and has a 14-Fr suction NFTS-UAS (GRIT, China) placed. The UAS’s head can be drawn past the renal pelvis-ureter junction when viewed directly through an 8.5-Fr ureteroscope (Karl Storz, Germany). The UAS’s back-end channel is then attached to the vacuum device (Figure 4). The water pressure does not surpass 25 mmHg, the negative pressure is 4–8 kPa, and the irrigation flow rate is 60–140 mL/min. By pressing the air hole with the thumb of the left hand during the procedure, the negative pressure is adjusted to maintain a satisfactory suction effect without rapidly drawing out the water in the renal pelvis. The frequency and power of the holmium laser are set to 10 hertz and 1.5 J., respectively. When necessary, the stones are moved and broken pieces of stone are recovered using the nickel-titanium basket (COOK, USA). Once the stone has been broken, the ureteroscope is used once more to verify that the suction UAS is positioned at the renal pelvis-ureter junction. A 5-F ureteral catheter is then inserted into the UAS using the ureteroscope, and its tip is positioned at the renal pelvis-ureter junction. To create an artificial water cycle, normal saline is injected at the end of the ureteral catheter (Figure 3). About 180 mL/min is the artificial water cycle flow rate, and for 20 to 40 seconds, the negative pressure is kept at 5 kPa. A 6-F double-J tube (KYB, China) is routinely placed after all renal calyces have been examined to ensure adequate fragmentation.

The time between the placement of the cystoscope and the successful implantation of the double-J stent was used to compute the operation time for the 2 patient groups. Usually, the double-J stent is kept in place for a month after surgery. If ureteral stenosis prevents the UAS from reaching the renal pelvis-ureter junction, a 6-F double-J (DJ) stent is inserted, and the procedure is repeated 1 month later. A non-contrast CT scan is conducted the first day following surgery to determine the effect of stone removal. “Complete stone removal” was defined as no residual stones or the diameter of residual stones was <2 mm. “Residual stones” was defined as presence of stones ≥2 mm in diameter. If necessary, follow-up surgery is done 1 month later.

Group 2 patients underwent percutaneous nephrolithotomy (Percutaneous renal access: GRIT GM-PNS-A1-18-20-s; Scope: Richard Wolf 8964.401). Under general anesthesia, the patient was initially positioned in the lithotomy position, during which a 5-F ureteral catheter was inserted into the ureter on the stone-bearing side to facilitate subsequent puncture site selection. The patient was then repositioned to the prone position, and the optimal puncture site was determined based on the stone’s location using B-mode ultrasound guidance. Artificial hydronephrosis was induced by injecting an appropriate volume of saline through the ureteral catheter to enhance visualization of the renal collecting system. Subsequently, a puncture was performed into the middle calyx of the posterior group of the affected kidney. A zebra guidewire was inserted through the puncture tract and advanced into the ureter. Percutaneous renal access was established by introducing a fascial dilator over the guidewire and dilating the tract to 20 French (F-20). A nephroscope was then inserted to inspect the renal pelvis and calyces. The stone was fragmented using an ultrasonographic lithotripter (EMS), and the resultant fragments were evacuated using irrigation fluid. The nephroscope was carefully maneuvered to inspect for any residual stones. An 18 French (F-18) nephrostomy tube was left in situ postoperatively for drainage.

STATISTICAL METHODS:

Preoperative and postoperative data were analyzed using GraphPad Prism 9 statistical software. Descriptive statistics were employed to characterize the study groups, with continuous data presented as mean±standard deviation (χ±SD). Comparisons between groups were performed using the independent-samples t test, while paired comparisons within groups were conducted using the paired t test. Categorical data were compared using the chi-square (χ²) test and are presented as counts or percentages (%). Missing data (<5% of variables) were managed via multiple imputation using fully conditional specification (FCS) after confirming missing data were random via Little’s MCAR test. A priori sample size calculation was performed using G*Power 3.1. Based on prior lithotripsy studies, we estimated a 25% difference in stone-free rates between the FURS and PCNL groups. With α=0.05, β=0.20 (80% power), and an allocation ratio of 1: 1, the analysis indicated a minimum requirement of 54 participants per group (total N=108). To account for potential attrition, we enrolled 337 patients (167 and 170, respectively). All analyses adhered to intention-to-treat principles. A two-sided P<0.05 was considered to indicate statistical significance.

Results

This retrospective study received ethics approval from the Institutional Review Board of the First Affiliated Hospital of Huzhou Normal College (Approval No.: 2024KYLL035-01), and all participants provided informed consent. Between March 2021 and January 2024, 430 renal calculi patients underwent surgical treatment at our institution. Patients were stratified into 2 groups by surgical approach: Group 1 (NFTS-UAS with FURS, n=193) and Group 2 (PCNL, n=237). The exclusion criteria were rigorously applied.

Stone size thresholds:

Exclusion of stones <2 cm (20 mm) from NFTS-UAS (Group 1) to focus on stones within the device’s therapeutic range (2–3.5 cm). We excluded stones >3.5 cm (35 mm) from PCNL (Group 2) to minimize confounding from extreme stone burdens requiring staged procedures.

Procedural crossovers:

In Group 1, we excluded 2 patients requiring conversion to PCNL due to ureteral strictures and 1 needing retroperitoneal laparoscopic ureterolithotomy. In Group 2, we excluded 24 patients due to concurrent flexible ureteroscopy (n=13), contralateral stone treatment during PCNL (n=5), incidental bladder tumors (n=3), or preoperative sepsis (n=3). After exclusions, 167 patients remained in Group 1 and 170 in Group 2 (Figure 1). All Group 1 patients underwent preoperative ureteral stenting (double-J catheter) for 1–2 weeks for ureteral dilation.

Baseline characteristics including age, sex, BMI, comorbidities (diabetes mellitus, hypertension, positive midstream urine culture), preoperative hemoglobin, renal stone burden/hardness, hydronephrosis, and operative side showed no significant intergroup differences (Table 1). Exceptions included preoperative white blood cell (WBC) (P=0.05), neutrophils (P<0.05), and stone location (P<0.01).

NFTS-UAS demonstrated shorter operative times (80.02±29.44 vs 98.95±28.82 minutes; P<0.01), reflecting reduced procedural complexity and enhanced efficiency of the suction-assisted technique. Clinically, this 19-minute difference translates to reduced anesthetic exposure and improved operating room throughput. Studies suggest every 15 minutes of reduced operative time decreases anesthesia-related complications (eg, postoperative nausea) by 12% and enhances surgical team efficiency by enabling 1–2 additional procedures per day in high-volume centers. Postoperative hospitalization was reduced with NFTS-UAS (45.62±30.59 vs 173.0±75.46 hours; P<0.01), equivalent to a 73% shorter stay. This accelerated discharge reduces nosocomial infection risks (estimated 3% daily risk in urological wards) and healthcare costs based on Chinese DRG reimbursement rates. The observed 127-hour difference aligns with PCNL’s requirement for nephrostomy management and aligns with global trends where minimally invasive techniques reduce length-of-stay by 50–80% compared to percutaneous approaches. These differences underscore the potential for NFTS-UAS to reduce healthcare resource utilization while maintaining efficacy (Table 2).

Preoperative antibiotic duration was shorter for NFTS-UAS (0.52±0.50 vs 1.58±1.85 days; P<0.01). There were no differences in postoperative creatinine (88.13±31.01 vs 88.52±51.1 μmol/L; P=0.93) or potassium (3.89±0.43 vs 3.91±0.40 mmol/L; P=0.65). These findings suggest comparable renal functional preservation and electrolyte stability across both techniques, consistent with prior studies where neither FURS nor PCNL significantly altered short-term renal biomarkers. We found significantly lower postoperative WBC in NFTS-UAS (8.70±4.0 vs 10.11±3.70×109/L; P<0.01). The PCNL group had a significantly higher post-/preoperative WBC rate (1.60±0.61; P<0.01) than the NFTS-UAS group (1.32±0.53). There was a significant difference between the postoperative blood neutrophil counts in the NFTS-UAS group (6.70±2.80×109/L) and the PCNL group (8.15±3.75×109/L) (P<0.01). The NFTS-UAS group’s postoperative blood hemoglobin was 141.10±15.23 (g/L), while the PCNL group’s was 134.20±17.04 (g/L), and the difference was statistically significant (P<0.01). There was a higher post-/preoperative hemoglobin ratio in the NFTS-UAS group (0.99±0.06 vs 0.93±0.08; P<0.01).

At 1 and 30 days after surgery, KUB imaging tests were performed on every patient. Patients who had unclear surgical views during the procedure or suspicious residual stone fragments based on KUB had CT scans. At postoperative day 1, the stone-free rate (SFR) was lower in the NFTS-UAS group (Day 1: 68.26% vs 83.53%; P<0.01), likely due to residual dust fragments requiring natural passage. By day 30, SFRs had equalized (Day 30: 88.62% vs 85.29%; P=0.42), indicating comparable long-term efficacy. Suspicious residual fragments were defined as radiographic opacities >2 mm on non-contrast CT, performed when intraoperative visualization was suboptimal or KUB suggested retained debris.

Neither group experienced any intraoperative problems. Overall complications were lower in the NFTS-UAS group (P<0.01). There was a significant difference in postoperative complications between the PCNL group and the NFTS-UAS group (P<0.01). The NFTS-UAS group had fewer infectious complications (eg, postoperative fever: 10 vs 91 cases; P<0.01) and reduced hemoglobin loss (141.1±15.23 vs 134.2±17.04 g/L; P<0.01). Subcapsular hematomas requiring percutaneous drainage occurred exclusively in the PCNL group (n=6), while steinstrasse was managed similarly (NFTS-UAS: 10, PCNL: 4). Ureteral strictures were more frequent with NFTS-UAS (n=11 vs 4; managed via stent replacement). One patient had renal artery embolism shown by digital subtraction angiography (DSA) after the nephrostomy tube was removed in the PCNL group. Complication classification followed Clavien-Dindo criteria (Table 3). Other complications, such as ureteral injury, ureteral rupture or tearing, severe bleeding, and acute renal failure, did not occur in either group.

For stone composition analysis, 147 patients in the NFTS-UAS group and 166 patients in the PCNL group were tested, showing no significant differences in composition (calcium oxalate predominance: 72% vs 68%; P=0.38). Analysis via infrared spectroscopy confirmed homogeneity, suggesting stone type did not confound outcomes. Calcium oxalate was the predominant type.

Discussion

According to current urological guidelines for the diagnosis and treatment of urinary calculi and the consensus of clinical experience, extracorporeal shock wave lithotripsy (ESWL) remains the standard treatment for upper urinary tract calculi <1 cm in diameter [9]. For larger renal stones (>1 cm), percutaneous nephrolithotomy (PCNL) and flexible ureteroscopic lithotripsy (FURS) are widely used, but their comparative efficacy and safety are debated [10,11]. While PCNL demonstrates versatility in managing stones of varying sizes, its requirement for channel dilation and nephrostomy tube placement elevates risks of urinary system injury and complications [12–15]. In contrast, FURS is favored for its minimally invasive profile and shorter learning curve; however, traditional FURS suffers from suboptimal stone clearance rates and intraoperative renal pelvic hypertension, predisposing patients to severe complications such as renal hemorrhage and urosepsis [16–19]. Current guidelines position FURS as a secondary option for stones >2 cm [20,21]. However, for patients with kidney stones with complex anatomy, such as horseshoe kidney and ureteropelvic junction obstruction (UPJO), who also need kidney reconstruction surgery, robotic pyelolithotomy is a more valuable treatment option when the kidney stone diameter is greater than 2 cm [8]. Recent innovations in laser systems, ureteroscope design, and accessory devices (eg, vacuum-assisted sheaths) have significantly enhanced the efficacy of FURS [22]. Numerous studies have demonstrated that flexible ureteroscopy can also address the significant burden of renal calculi using high-performance lasers, vacuum suction lithotripsy devices, and staged operations. Breda et al [23] achieved satisfactory stone-free rates (SFRs) for stones >2.5 cm using holmium laser FURS, and Lai et al [24] eventually attained a stone-free rate comparable to that of percutaneous nephrolithotomy (PCNL) by incorporating the use of suction ureteral sheath in the lithotripsy of kidney stones measuring 2–4 cm. According to recent research, performing FURS with a suction sheath can lessen the difficulty of the surgical procedure, lower intraoperative renal pelvic pressure, and lessen renal parenchymal damage, all of which help to prevent iatrogenic trauma [25]. In recent years, the suction ureteral sheath has become a more popular material for flexible ureteroscopy. During laser lithotripsy, the flexible ureteroscope sheath with vacuum suction function can directly remove the stone dust, in contrast to the conventional ureteral sheath. In addition to maintaining a clearer surgical field and lowering renal pelvic pressure, this increases the stone clearance rate [26,27].

The study demonstrated that while PCNL achieved a higher initial stone-free rate (83.53% vs 68.26%) for 2–3.5 cm renal calculi, FURS with the novel flexible-tip suctioning ureteral access sheath (NFTS-UAS) provided equivalent long-term efficacy by 30 days (88.62% vs 85.29%, P<0.05). These results align with recent advancements in suction-assisted FURS. For instance, Lai et al [24] reported an 87% 30-day SFR for 2–4 cm stones using similar suction sheaths, closely mirroring our findings (88.62%). However, our day-1 SFR (68.26%) was lower than the 75–80% rates observed in meta-analyses of suction FURS [28], likely due to our stringent residual fragment definition (>2 mm) compared to the >4 mm thresholds used in prior studies. The NFTS-UAS group exhibited significant advantages, including reduced postoperative complications (eg, fever, infections, hemorrhage), shorter operation time, faster recovery (lower antibiotic use, shorter hospitalization), and decreased hemoglobin loss and inflammatory responses compared to PCNL (P<0.05). However, rare but serious complications, such as postoperative renal abscess, have been reported with similar suctioning sheath systems [29], underscoring the importance of meticulous intraoperative sterility and postoperative monitoring. These findings suggest that while NFTS-UAS with FURS reduces complication risks overall, clinicians must remain vigilant to mitigate rare adverse events. No significant difference in stone composition or proportion was observed between the 2 groups of patients who agreed to undergo stone analysis following surgery (P=0.38). Despite higher consumables costs, NFTS-UAS with FURS reduced total hospitalization expenses, likely due to fewer complications and shorter stays. These findings highlight NFTS-UAS as a minimally invasive, cost-effective alternative to PCNL for intermediate-sized stones, balancing efficacy with enhanced safety and recovery. Further research is warranted to validate its role in larger stone burdens.

Our study introduces the novel flexible-tip suctioning ureteral access sheath (NFTS-UAS), which addresses key limitations of conventional systems through: a 10-cm flexible tip (160° deflection) for enhanced calyceal access, real-time stone dust clearance to maintain visual clarity, stabilized intrarenal pressure to minimize infection risks; and reduced basket dependency for decreased mechanical trauma. Key advantages include: (1) enhanced maneuverability, generating localized vortices for effective stone clearance; (2) continuous visualization during lithotripsy, reducing residual fragments and repeated interventions; (3) reduced reliance on baskets, minimizing mechanical trauma during stone retrieval; (4) stabilized intrarenal pressure, lowering risks of infection, renal injury, and postoperative complications (eg, fever incidence: 10 vs 91 patients in FURS vs PCNL); and (5) simplified integration with existing equipment, requiring minimal training. While NFTS-UAS demonstrates superior safety and efficiency for 2–3.5 cm stones compared to PCNL, its benefits must be contextualized with study limitations. This study has several limitations that warrant consideration. First, the retrospective, single-center design introduces inherent biases, including selection bias due to non-randomized patient allocation. For instance, surgeon preference for PCNL in anatomically complex cases may have skewed the patient population toward less challenging cases in the NFTS-UAS group. Second, the lack of patient matching based on critical variables such as age, BMI, and stone location (with significant intergroup differences in preoperative WBC and stone distribution) introduces potential confounding. Third, our sample size, while adequate for primary outcomes, limited subgroup analyses, particularly for infection-related stones, which comprised only 12% of the cohort. Fourth, the 30-day follow-up period precludes assessment of long-term outcomes such as stone recurrence rates or chronic renal function deterioration, which are critical for evaluating the durability of NFTS-UAS. Finally, unmeasured confounders, including variations in surgeon experience (procedures were performed by 3 surgeons with 3–15 years of experience) and patient adherence to postoperative care protocols, may have influenced outcomes. These limitations underscore the need for prospective, multicenter studies with standardized protocols to validate our findings. NFTS-UAS with FURS offers a safer, minimally invasive alternative to PCNL for intermediate renal stones, with advantages in suction efficiency, complication reduction, and procedural simplicity.

While the novel flexible-tip suctioning ureteral access sheath (NFTS-UAS) enhances flexible ureteroscopic lithotripsy for 2–3.5 cm renal stones, which is similar to the stone-free rate of percutaneous nephrolithotomy that other authors have documented [30], its application faces limitations dependent on stone characteristics and anatomical factors. Larger stone burdens (>3.5 cm), particularly staghorn calculi, remain better suited to PCNL due to reduced NFTS-UAS efficacy in prolonged procedures and higher residual fragment rates. Similarly, lower-pole stones with narrow infundibular angles limit sheath maneuverability, often necessitating basket retrieval and prolonging surgery. Hard stones pose additional challenges, as incomplete laser fragmentation risks sheath obstruction, requiring repeated scope withdrawal or pelvic flushing to clear debris. Despite these constraints, NFTS-UAS demonstrates advantages over PCNL in managing residual fragments, minimizing trauma, and reducing postoperative complications (eg, fever rates). The NFTS-UAS is a promising advancement in minimally invasive stone management, but its broader adoption requires rigorous validation.

We propose 5 main research priorities:

1) Multicenter randomized controlled trials (RCTs) comparing NFTS-UAS with PCNL for 2–3.5-cm stones, stratified by stone density and location, to standardize efficacy and safety metrics. 2) Technical optimization studies investigating use of adjunct tools (eg, high-power lasers, ultrasonic suction devices) to improve NFTS-UAS efficacy for hard stones and lower-pole calculi. 3) Long-term outcomes research with extended follow-up studies to assess stone recurrence rates and renal function preservation, particularly for infectious stones. 4) Cost-benefit analyses, with economic evaluations comparing NFTS-UAS (with reduced hospitalization) against PCNL in diverse healthcare systems. 5) Training and standardization to develop simulation-based training protocols to ease the learning curve and evaluate outcomes across surgeon experience levels.

The NFTS-UAS expands the scope of FURS for intermediate renal stones, yet its role in complex scenarios requires further refinement. By addressing these research gaps, future studies can establish evidence-based guidelines for sheath utilization, optimize its integration with emerging technologies, and solidify its position as a first-line option for select groups of patients with renal stones. Collaborative efforts to standardize protocols and validate outcomes will be critical to maximizing its clinical impact.

Notwithstanding the aforementioned drawbacks, flexible-tip ureteroscopic lithotripsy will likely remain a competitive alternative to percutaneous nephrolithotomy with the assistance of newly-developed equipment and methods. In later stages, the introduction of new lasers like the ultra-pulse thulium laser and the popularity of more slender flexible ureteroscopy can improve the sheath ratio and enhance stone pulverization efficacy [22], which will increase the effectiveness of vacuum pressure stone removal. Compared to randomized, double-blind, controlled studies, this study comparing NFTS-UAS and PCNL for renal stones provides valuable insights but is limited by several methodological factors. Notably, the lack of patient matching based on key characteristics such as age, BMI, and stone location introduces potential confounding and limits the comparability of the 2 groups. Additionally, the significant exclusions based on stone size and prior interventions may have introduced selection bias, while the imbalance in stone location distribution further complicates the interpretation of outcomes. The study also lacked longer-term follow-up to fully assess the durability of stone clearance and late complications. Differences in preoperative blood WBC and neutrophil levels could have influenced postoperative inflammatory responses and infection rates, potentially skewing the results. Future studies should address these limitations through rigorous patient matching, extended follow-up, and standardized reporting to enhance the reliability and generalizability of comparative outcomes between NFTS-UAS and PCNL.

Conclusions

The findings of this study contribute meaningfully to the advancement of urology science and offer insights with potential relevance to clinical practice. With stone-free rates comparable to PCNL, combined with reduced invasiveness, faster recovery times, and fewer complications, the novel flexible-tip suctioning ureteral access sheath used with FURS is a promising alternative for managing renal calculi measuring 2–3.5 cm. Being less invasive, with quicker recovery and fewer complications, these outcomes suggest that this approach could support a gradual shift toward more patient-friendly and cost-effective interventions, aligning with broader trends in minimally invasive urologic care. However, further validation through prospective randomized controlled trials is essential to confirm these findings, assess long-term outcomes, and explore applications in larger or more complex calculi.

This study demonstrates that the novel flexible-tip suctioning ureteral access sheath (NFTS-UAS) combined with FURS achieves 30-day stone-free rates comparable to PCNL (88.62% vs 85.29%, P=0.42) for 2–3.5 cm renal calculi, while offering distinct advantages in procedural safety and recovery metrics. Specifically, NFTS-UAS reduced operative time by 19 minutes (80.02 vs 98.95 minutes, P<0.01), shortened hospitalization by 73% (45.6 vs 173.0 hours, P<0.01), and reduced postoperative complications (eg, 10 vs 91 fever cases, P<0.01). These outcomes align with the device’s design goals of minimizing invasiveness and optimizing stone clearance efficacy through real-time suction and pressure stabilization.

While these results suggest NFTS-UAS as a viable alternative to PCNL for intermediate-sized stones, its clinical impact requires cautious interpretation. The retrospective design, lack of randomization, and unmatched patient cohorts (eg, 23% lower-pole stones in PCNL vs 11% in NFTS-UAS) limit causal inferences. Furthermore, the 30-day follow-up precludes conclusions about long-term outcomes such as recurrence, which typically occurs beyond 6 months.

Prospective validation is critical, particularly multicenter randomized trials controlling for stone location, density, and surgeon experience, to confirm the observed 30-day efficacy (88.62% SFR) and safety advantages (6.6% ureteral strictures vs PCNL’s 3.5%). Until such evidence emerges, NFTS-UAS should be considered a complementary option rather than a definitive replacement for PCNL, particularly in anatomically complex cases or larger stone burdens (>3.5 cm) where percutaneous approaches retain superiority.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.