Flexible and navigable suction ureteral access sheath versus traditional ureteral access sheath for flexible ureteroscopy in renal and proximal ureteral stones: a meta-analysis of efficacy and safety

Abstract

Background

Traditional ureteral access sheaths (T-UAS) are limited by rigidity and lack of suction, potentially increasing complications. Flexible and navigable suction ureteral access sheaths (FANS-UAS) offer improved maneuverability and active suction, but comparative evidence on their efficacy and safety is scarce. This meta-analysis evaluates FANS-UAS versus T-UAS in flexible ureteroscopy (fURS).

Methods

A systematic search across PubMed, Embase, Cochrane Library, and Web of Science (from inception to February 2025) identified studies comparing FANS-UAS and T-UAS. Included were RCTs and observational studies with ≥ 20 patients. Outcomes included stone-free rates (SFRs), operative time, hospital stay, and complications. Study quality was assessed using the Jadad Scale for RCTs and Newcastle-Ottawa Scale (NOS) for observational studies.

Results

Eight studies (1 RCT, 7 observational; 1,816 patients: 866 FANS-UAS, 950 T-UAS) were analyzed. Compared to T-UAS, FANS-UAS demonstrated significantly higher stone-free rates (SFRs) at both postoperative day 1 (OR = 4.01, 95% CI: 1.98–8.11) and 30-day follow-up (OR = 2.37, 95% CI: 1.62–3.46). FANS-UAS was associated with a lower risk of postoperative fever (OR = 0.31, 95% CI: 0.21–0.47). Operative time trended longer with FANS-UAS (MD = 2.64 min, 95% CI: −2.56 to 7.84; p = 0.32), though without statistical significance, while hospital stay showed no difference between groups (MD = − 0.07 days, 95% CI: −0.16 to 0.01; p = 0.1).

Conclusion

FANS-UAS provides superior stone clearance and reduced complications versus T-UAS, with only slightly longer operative time. The integrated suction system enables these advantages through improved fragment removal and pressure control. Further RCTs should confirm these benefits.

Introduction

Flexible ureteroscopy (fURS) has established itself as the first-line treatment for renal calculi ≤ 2 cm and proximal ureteral stones ≥ 1 cm, as endorsed by the 2025 European Association of Urology (EAU) guidelines on urolithiasis [1]. This minimally invasive approach offers distinct advantages over percutaneous nephrolithotomy (PCNL) in terms of reduced morbidity while maintaining superior stone-free rates compared to shock wave lithotripsy (SWL) for the specified stone sizes. Ureteral access sheaths (UAS) play a pivotal role in fURS by facilitating instrument passage, improving irrigation flow, and reducing intrarenal pressure (IRP) [2, 3]. However, traditional UAS (T-UAS) designs are often constrained by rigidity, limited maneuverability, and the absence of active suction, which may contribute to complications such as postoperative infection and elevated IRP during prolonged procedures [4].

Recent technological innovations have yielded a paradigm shift in UAS development with the advent of flexible and navigable suction UAS (FANS-UAS). This platform integrates three transformative features: (1) biomimetic atraumatic tip configurations minimizing mucosal contact stress, (2) segmental flexibility enabling active renal calyceal navigation, and (3) integrated aspiration channels for fragment evacuation and pressure homeostasis [5,6,7,8]. Preliminary evidence suggests these design advancements may synergistically enhance clinical outcomes through multiple pathways: optimizing stone clearance efficiency via real-time debris removal, reducing infectious risks through prompt irritant extraction, and maintaining physiologic IRP via dynamic pressure regulation [9,10,11,12,13]. Despite these theoretical advantages, current comparative data remain inconclusive due to methodological constraints in existing studies, including inadequate power from limited cohort sizes, procedural heterogeneity, and non-standardized endpoint reporting.

To date, no systematic synthesis has evaluated the efficacy and safety of these novel UAS against conventional designs. This comprehensive meta-analysis therefore seeks to address this critical knowledge gap through dual objectives: to quantitatively compare clinical efficacy (stone-free rates) and safety profiles (complication spectra) between FANS-UAS and T-UAS in contemporary fURS practice.

Methods

This meta-analysis was not prospectively registered in a systematic review registry. However, to ensure methodological rigor and transparency, the study was conducted in strict accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline [14].

Literature search strategy

A systematic search was conducted across PubMed, Embase, Cochrane Library, and Web of Science from inception to February 2025. Key search terms included: “suction ureteral access sheath”, “Aspiration-Assisted ureteral access sheath”, “Vacuum-assisted ureteral access sheath”, “flexible ureteroscopy”, and “urolithiasis”. Given the lack of standardized terminology for flexible and navigable suction ureteral access sheath, we implemented an inclusive search strategy designed to capture all potentially relevant studies regardless of specific device nomenclature. Manual searches of reference lists from relevant reviews and conference proceedings were performed to identify additional studies.

The titles and abstracts of studies obtained through this search strategy were reviewed for inclusion by two reviewers (LQ, ZT). Any discrepancies were resolved by a final reviewer (ZSX). Studies were included if they met the following criteria: Randomized controlled trial (RCT) or observational cohort studies (prospective/retrospective) directly comparing FANS-UAS versus T-UAS in fURS for stone management. Exclusion criteria included case reports, animal studies, non-English articles, or studies with fewer than 20 patients.

Data extraction and quality assessment

Two reviewers (LQ, ZT) independently extracted data using a standardized form. Study characteristics included author, year, design, sample size, stone location and size, and UAS specifications (e.g., diameter, suction mechanism). Outcomes of interest were primary (SFR at postoperative day 1 and 30 days) and secondary (operative time, postoperative infection, and hospital stay).

Methodological quality assessment

The methodological quality of the included studies was assessed using validated tools appropriate to their study design. Two independent reviewers (LQ, ZT) evaluated each study, and any discrepancies were resolved through discussion or by consulting a third reviewer (ZSX) for consensus. RCTs were evaluated using the Jadad Scale, a 5-point scoring system assessing randomization, blinding, and withdrawals/dropouts. Studies scoring ≥ 3 were classified as high quality, while scores < 3 indicated low quality. Retrospective cohort studies were assessed using the Newcastle-Ottawa Scale (NOS), which evaluates selection, comparability, and outcome domains. Studies were awarded stars (maximum 9), with ≥ 7 stars indicating high quality, 5–6 moderate, and < 5 low quality.

Statistical analysis

The statistical analysis was conducted using RevMan 5.4 software, with a focus on preparing and synthesizing data to ensure robust and transparent results. For handling missing data, attempts were made to contact corresponding authors to obtain unreported summary statistics, such as means, standard deviations, or confidence intervals. Incomplete outcome data, such as dropouts or loss to follow-up, were assessed for bias, and studies with less than 10% missing data were included without imputation, whereas sensitivity analyses were performed for studies with significant missing data to evaluate their impact on the results. For continuous outcomes, mean differences (MDs) or standardized mean differences (SMDs) were calculated based on the similarity of measurement scales. Meta-analyses were performed using a random-effects model to account for heterogeneity, which was assessed using the Chi² test and I² statistic, with I² >25% indicating substantial heterogeneity. Results were presented in forest plots, displaying effect sizes and 95% confidence intervals (CIs) for individual studies and pooled estimates. Publication bias was assessed using funnel plots and Egger’s test when at least 10 studies were included in the meta-analysis.

Results

Study selection

The flow diagram (Fig. 1) summarizes the study selection process. Initial database searches identified 255 records, with 110 remaining after duplicate removal. Title and abstract screening excluded 88 studies, leaving 23 for full-text assessment. After applying inclusion criteria, eight studies (1 RCT and 7 cohort studies) were included in the final meta-analysis [15,16,17,18,19,20,21,22].

Study characteristics

The analysis included 866 patients managed using FANS-UAS and 950 patients treated with T-UAS. The stone burden varied between studies, with reported stone sizes ranging from 1 to 3 cm in diameter. Eight study arms primarily focused on renal stones, three studies also included cases involving proximal ureteral stones [15, 21, 22]. The eight included studies universally employed stone diameter for stone burden assessment, with one study adding stone volume evaluation and another utilizing both volume and surface area measurements. Among the eight included studies, five defined stone-free status as < 2 mm residual fragments, two required fragments < 3 mm, and one study adopted the strictest criterion of zero fragments. Ureteral access sheath sizes ranged from 9.5/11.5 Fr to 13/15 Fr. A comprehensive summary of operative techniques and assessment methodologies is provided in Table 1.

Table 1 Characteristics of the included studies

Methodological quality assessment

The single RCT scored 4/5 on the Jadad Scale, indicating high quality. The seven retrospective studies scored 7–8 stars on the NOS, reflecting high quality (Table 2). The RCT exhibited low risk of bias in randomization and attrition but raised concerns in blinding due to procedural limitations. Retrospective studies, while controlling for confounders, were susceptible to selection bias and residual confounding from unmeasured factors such as surgeon expertise.

Table 2 The quality assessment of included studies by the Newcastle-Ottawa quality assessment form for cohort studies

Stone-Free rate

The use of FANS-UAS demonstrated significantly higher stone-free rates compared to T-UAS, with an odds ratio (OR) of 4.01 (95% CI: 1.98–8.11) on postoperative day 1 (Fig. 2). This advantage persisted at the 30-day follow-up, though the effect size was slightly reduced (OR = 2.37, 95% CI: 1.62–3.46, Fig. 3).

Operative time

Pooled analysis of six studies revealed a trend toward longer operative time in the FANS-UAS group (MD = 2.64 min, 95% CI: -2.56 to 7.84, p = 0.32, Fig. 4). While this difference did not reach statistical significance, the upper bound of the confidence interval suggests a clinically relevant prolongation of operative time under certain conditions. Heterogeneity across studies was high (I² = 87%).

Length of hospital stay

Meta-analysis of four studies demonstrated no statistically significant difference in the length of hospital stay between the FANS-UAS and T-UAS groups (MD = -0.07 days, 95% CI: -0.16 to 0.01, p = 0.1, Fig. 5).

Complication rates

Five studies (FANS-UAS: n = 582; T-UAS: n = 570) reported overall complications, with 44 events in the FANS-UAS group and 122 in the T-UAS group. The pooled analysis showed a significantly lower complication rate in the FANS-UAS group (OR 0.30, 95% CI: 0.21–0.43, Fig. 6), with no heterogeneity (I² = 0%, P = 0.42).

Postoperative fever

Eight studies (FANS-UAS: 32/859; T-UAS: 102/942) reported postoperative fever. The FANS-UAS group had a significantly reduced risk (OR 0.31, 95% CI: 0.21–0.47), with no heterogeneity (I² = 0%, P = 0.95, Fig. 7).

Discussion

This meta-analysis of 1,816 patients from eight studies provides the first comprehensive comparison of FANS-UAS versus T-UAS in fURS for stone management. The results demonstrate that FANS-UAS significantly improves stone-free rates at both immediate and intermediate follow-up while lowering the risk of postoperative fever and other complications. These findings align with the proposed mechanistic advantages of suction-assisted sheaths, including enhanced intraoperative visualization, reduced retropulsion, and lower IRP, which collectively contribute to more efficient stone clearance and fewer infectious complications [2, 12, 23,24,25].

The superior SFR observed with FANS-UAS likely reflects its integrated suction capability, which actively evacuates stone fragments, minimizing residual debris that could obscure visualization or lead to retained fragments. This aligns with prior hypotheses that suction-assisted sheaths mitigate retropulsion, a common challenge in T-UAS use, particularly for larger (1–3 cm) or proximal ureteral stones. The significant reduction in postoperative fever in the FANS-UAS group further supports its role in lowering IRP, potentially reducing pyelovenous backflow and bacterial translocation—key contributors to infectious complications.

While the extended operative time observed in FANS-UAS procedures deserves attention, this phenomenon may be attributed to fundamental differences in stone management strategies between traditional UAS (T-UAS) and suction-assisted systems. In conventional T-UAS procedures, prolonged laser lithotripsy time is typically required to achieve “dust-like” fragmentation (< 1 mm) that facilitates spontaneous passage through natural urinary drainage. Conversely, FANS-UAS introduces a paradigm shift by enabling active extraction of larger stone fragments (2–4 mm) through its suction-irrigation system. This technical advantage reduces laser lithotripsy duration by eliminating the need for excessive stone pulverization, but simultaneously introduces additional time expenditure for meticulous fragment aspiration under direct vision. Importantly, the temporal redistribution - saving lithotripsy time at the expense of extended fragment retrieval - might explain the comparable total operative time between the two modalities in early clinical experience.

From a clinical outcomes perspective, the active fragment removal mechanism of FANS-UAS may confer hidden advantages beyond operative metrics: (1) Reduced risk of residual “stone street” formation compared to passive drainage-dependent systems; (2) Potential mitigation of postoperative colic episodes caused by fragment migration; (3) Enhanced clearance efficiency for infection-prone struvite stones requiring complete debris removal. Future studies should investigate whether the learning curve-associated time delay in FANS-UAS could be offset by reduced secondary procedures through improved primary stone clearance rates.

Several limitations should be acknowledged. First, the predominance of retrospective designs introduces risks of selection bias regarding sheath allocation and unmeasured confounders. Second, clinical heterogeneity in sheath sizes and surgical protocols may affect generalizability. Third, the inability to perform subgroup analyses due to limited data restricts more nuanced interpretations. Fourth, the included studies had relatively short follow-up periods (1–3 months), which precludes assessment of delayed complications such as ureteral strictures - a theoretically important consideration given the need to pass the access sheath beyond the pelviureteric junction in FANS-UAS procedures. Longer-term studies are needed to evaluate this potential risk.

Despite these limitations, this study has important strengths as the first meta-analysis directly comparing FANS-UAS and T-UAS, pooling data from 8 studies and 1,816 patients. The results demonstrate clinically meaningful advantages of FANS-UAS, including a 4-fold higher immediate stone-free rate (OR 4.01, 95% CI 1.98–8.11) and a 69% reduction in postoperative fever (OR 0.31, 95% CI 0.21–0.47). Notably, these benefits were achieved without significantly prolonging operative time (MD 2.64 min, p = 0.32) or hospital stay (MD -0.07 days, p = 0.1). The substantial decrease in overall complications (OR 0.30, 95% CI 0.21–0.43) further supports FANS-UAS as a valuable advancement in ureteroscopy, particularly for cases where infection risk or stone clearance is a major concern.

Moving forward, future research should prioritize multicenter RCTs with standardized protocols to validate these findings and address current limitations. Key areas for investigation include defining optimal sheath parameters for varying stone burdens, assessing long-term safety outcomes such as ureteral stricture rates and renal function preservation, evaluating cost-effectiveness, and quantifying procedural efficiency gains associated with the surgeon learning curve.

Conclusion

As the first systematic comparison of FANS-UAS and traditional UAS platforms, this meta-analysis establishes that suction-assisted ureteroscopy represents a meaningful evolution in endoscopic stone management. By enabling active fragment retrieval while maintaining stable intrarenal pressures, the technology addresses two longstanding challenges in flexible ureteroscopy: residual fragment clearance and infectious complications. The clinical benefits are particularly relevant for complex calculi and infection-prone scenarios where complete stone removal is paramount.

These findings should encourage wider adoption of FANS-UAS in appropriate clinical settings, while highlighting the need for standardized protocols to optimize its use. Future investigations should focus on refining patient selection criteria and evaluating the economic implications of reduced complication rates. Ultimately, this technology marks an important step toward safer and more effective minimally invasive stone treatment.

Fig. 1

Study flow chart outlining the systematic search strategy and study selection process

Fig. 2

Forest plot displaying the effect of FANS-UAS versus T-UAS on stone-free rate at postoperative day 1

Fig. 3

Forest plot displaying the effect of FANS-UAS versus T-UAS on stone-free rate at postoperative day 30

Fig. 4

Forest plot displaying the effect of FANS-UAS versus T-UAS on operative time

Fig. 5

Forest plot displaying the effect of FANS-UAS versus T-UAS on length of hospital stay

Fig. 6

Forest plot displaying the effect of FANS-UAS versus T-UAS on complication rates

Fig. 7

Forest plot displaying the effect of FANS-UAS versus T-UAS on postoperative fever