Impact of positioning of ureteral access sheath in patients undergoing flexible ureteroscopy for renal stone treatment: a retrospective observational study

Introduction

Background

In recent decades, the global prevalence of kidney stones has increased significantly, currently affecting nearly 1 in 11 individuals in the United States (1). This upward trend spans both sexes, reflecting a growing public health concern in urology. A key driver of this rise is the higher prevalence of metabolic syndrome—a multifactorial condition characterized by obesity, hypertension, insulin resistance, and dyslipidaemia (2). The escalating incidence of nephrolithiasis is expected to impose a substantial economic burden on healthcare systems (3,4), with rising costs associated with diagnosis, treatment, and long-term management (5).

In this context, flexible ureteroscopy (fURS) has become a gold-standard approach for managing renal and proximal ureteral stones due to its minimally invasive profile and high efficacy (6). A critical component of fURS success is the use of ureteral access sheaths (UASs), which enable repeated renal access, optimize irrigation by facilitating fluid outflow, and enhance visualization through reduced intrarenal pressure (7,8). These technical advantages have expanded the indications for endourological interventions, establishing fURS as a first-line treatment for larger and more complex stone burdens (9).

Rationale and knowledge gap

Although flexible UASs and suction sheaths with novel ureteroscopes are gaining popularity due to their improved manoeuvrability and reduced ureteral trauma risk (10), traditional UAS remain widely used in clinical practice (11,12). Their continued preference stems from proven efficacy, cost-effectiveness, and extensive surgical familiarity (13). Additionally, rigid or semi-rigid sheaths may offer advantages in cases involving ureteral strictures or challenging anatomy due to their superior stability and insertion predictability (14). While advancements in flexible UAS design aim to overcome limitations such as kinking and suboptimal irrigation flow (15), the optimal choice between sheath types should be guided by patient-specific factors, procedural requirements, and surgeon expertise (16).

Although suction sheaths and novel ureteroscopes are gaining popularity, traditional UAS remain widely adopted in many institutions due to accessibility, cost considerations, and surgeon familiarity.

Objectives

Our study aims to evaluate the influence of UAS positioning during fURS for renal stone management on clinical outcomes. The primary objective is to determine the impact of UAS placement on the stone-free rate (SFR) at 30 days, defined as the absence of residual calculi or fragments ≤4 mm (17) on kidney-ureter-bladder (KUB) radiography or computed tomography (CT).

Secondary objectives include assessing the association between UAS positioning and (I) operative time, (II) intraoperative complications (e.g., ureteral injury or bleeding), (III) postoperative complications (e.g., infection or ureteral stricture), and (IV) duration of postoperative hospitalization.

By systematically analysing these outcomes, this study seeks to clarify whether variations in UAS placement influence surgical efficacy and patient recovery. Furthermore, we aim to address a critical gap in the literature by providing evidence-based insights into the optimal use of UAS in fURS. The findings may contribute to refining surgical techniques, enhancing procedural efficiency, and improving postoperative care in renal stone management. Ultimately, this investigation strives to inform clinical decision-making and support the development of standardized guidelines for UAS utilization in endourological practice. We present this article in accordance with the STROBE reporting checklist (available at https://asj.amegroups.com/article/view/10.21037/asj-25-54/rc).

Methods

Study design and ethical details

A retrospective analysis was conducted on consecutive patients who underwent fURS for renal stones at our institution (Department of Urology in University of Campania “Luigi Vanvitelli”, Naples) between June 2022 and June 2024. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments on ethical principles for medical research involving human subjects (18). The study was approved by our Local Institutional Review Board A.O.U. Federico II – A.O.R.N. Cardarelli (ID-312015) and informed consent was taken from all individual participants for the inclusion of their data in the database and for their use for scientific research purposes.

Patient enrollment

Patients were enrolled based on the presence of renal stones and stratified into two groups according to the use of different access sheaths. Eligible participants were healthy adults aged 18–75 years with CT-confirmed kidney stones (≤2 cm in diameter) with an estimated glomerular filtration rate (eGFR) of ≥60 mL/min/1.73 m².

Exclusion criteria comprised: (I) age <18 or >75 years; (II) presence of pyuria or ureteral stones; (III) renal parenchymal thinning ipsilateral to the stone; (IV) history of recent surgery; (V) chronic kidney disease (CKD) or solitary kidney; (VI) use of nephrotoxic agents; (VII) prior stone surgery within the last 3 months; (VIII) preoperative diagnosis of ureteral stricture precluding ureteroscopy; and (IX) inability to insert a UAS. Patients meeting any exclusion criteria or presenting incomplete demographic, surgical, or outcome data were omitted from the final analysis. The selection and exclusion criteria are summarized in Figure 1.

Figure 1 Flow diagram of patient selection. CKD, chronic kidney disease; FU, follow-up; fURS, flexible ureteroscopy; UAS, ureteral access sheath; UTI, urinary tract infection.

Patient evaluation

A comprehensive diagnostic workup was employed for the initial assessment, including abdominal ultrasonography, KUB radiography, blood tests, and urinalysis. Prior to surgery, all patients underwent urine culture and contrast-enhanced CT scans.

Subsequent data analysis encompassed both demographic and clinical-surgical parameters. Demographic variables, stone characteristics (size, number, and location), hospitalization duration, operative time, pre- and postoperative stent placement, SFR, and postoperative complications were evaluated. Complications were classified according to the modified Clavien-Dindo grading system (19).

Data collection and statistics

Patient data were systematically collected and recorded in a standardized Microsoft Excel database (Microsoft Corp., Redmond, WA, USA) for subsequent analysis. All statistical analyses were performed using MedCalc Statistical Software version 20.218 (MedCalc Software Ltd., Ostend, Belgium). UAS positioning was classified into two distinct groups: juxta-pelvic placement (Group A) or ureteral placement (Group B). The dataset encompassed comprehensive patient characteristics, including: demographic variables (age, sex), comorbid conditions (hypertension, diabetes mellitus, hypothyroidism, ischemic heart disease, peripheral atherosclerosis), anatomical parameters (presence of renal abnormalities, laterality of calculi), stone characteristics (number, radiographic features), renal function indicators (preoperative creatinine levels, presence of hydronephrosis, pre- and post-operative renal insufficiency).

Statistical analysis

Data normality was assessed using the Shapiro-Wilk test. Continuous variables were expressed as medians with interquartile ranges (IQRs), while categorical variables were reported as absolute counts and percentages. Comparative analyses employed the Mann-Whitney U test for non-normally distributed continuous variables and Pearson’s chi-square test for categorical variables. Post-hoc power analysis for the primary outcome (30-day SFR) was performed using an expected success rate of 85% per group, a two-sided α=0.05, and a 15% non-inferiority margin. With 64 total patients (juxta-pelvic n=37 vs. intra-ureteral n=27), the achieved power was approximately 81%, confirming adequate sensitivity to detect moderate differences between groups. The primary outcome analysis examined the association between UAS positioning and 30-day SFR, defined as either complete clearance or residual fragments ≤4 mm on postoperative imaging (KUB radiography or non-contrast CT). A P value threshold of 0.05 was arbitrarily set for statistical significance. RStudio was used to perform the analyses. The standardized data collection protocol and predefined analytical strategy minimized potential biases and enhanced the reliability of our findings. Given the 30-day follow-up, the occurrence of ureteral strictures cannot be adequately assessed within this timeframe.

Surgical procedure and patient management

All procedures were performed by a senior surgeon with experience of >1,000 retrograde intrarenal surgery (RIRS) cases (M.D.S.). All procedures were performed under general anesthesia following the steps of the technique as described by Traxer (20), with a 7.5-F flexible ureteroscope (Flex X2, Karl Storz GmbH & Co. KG, Tuttlingen, Germany) and using a 10–12 Fr UAS (ReTrace, Coloplast A/S, Humlebæk, Denmark), positioned in juxta-pelvic or ureteral position depending on surgeon preference and based on the facility of UAS advancement through the ureteral lumen. Holmium 20-watt laser (RevoLixDuo, LISA Laser products, Katlenburg-Lindau, Germany) was utilized for lithotripsy with a 272-micron fiber, dusting setting (0.5–0.6 J; 12–15 Hz), and the largest fragments were extracted with a nitinol basket and were sent for stone analysis. At the end of procedure, a JJ stent was placed.

Follow-up

All patients underwent follow-up visits at 7 and 30 days. At first FU visit, patients underwent clinical examination and US; at second FU, complete blood count, renal function tests and KUB or CT scan were performed. KUB was performed in all patients with preoperative radiopaque stone, CT scan without contrast was preferred in patients with preoperative radiolucent stone. Double J stent was removed 30 days after surgery in patients without significant residual stones.

Results

Baseline patient characteristics and overall outcomes

A total of 64 patients undergoing kidney stone treatment via fURS with UAS placement were included in this study. Baseline patient characteristics are summarized in Table 1. The median age of the cohort was 64 (IQR, 53–73) years, with a gender distribution of 40.6% male and 59.4% female. Genitourinary abnormalities—including horseshoe kidney, ureteropelvic junction stenosis, genitourinary prolapse, renal atrophy, and ureteral stenosis—were present in 15.6% of patients. Stone composition analysis revealed that 64% of calculi were calcium oxalate (39% monohydrate, 25% dihydrate), 5% were cystine stones, 9% were calcium phosphate stones and 22% were uric acid stones, with no significant difference in distribution between Group A and Group B. The median stone hardness was 1,458 (IQR, 970–2,100) Hounsfield units, with no statistically significant differences identified between Group A and Group B (P=0.98). Radiopaque stones were identified in 40.6% of cases, while 59.4% were radiolucent. The median stone size was 12 mm (range, 7–20 mm), with solitary stones observed in 73.4% of patients and multiple stones in 26.6%. Stone location analysis demonstrated homogeneous distribution across the general cohort and between groups (P>0.05). Hypertension was reported in 17.2% of patients, while hypothyroidism, diabetes mellitus, and ischemic heart disease were present in 7.8%, 10.9%, and 6.2%, respectively. Additionally, 42.2% of stones were localized to the left kidney, and 9.4% of patients had peripheral atherosclerosis. Preoperative hydronephrosis and renal insufficiency were each present in 10.9% of cases. UAS positioning was juxta-pelvic in 57.8% of procedures and ureteral (distal/proximal) in 42.2%, primarily due to stricture-related adaptations. Surgical and postoperative outcomes are detailed in Table 2. The median operative time was 74.5 (IQR, 53.5–92.5) min, with a median hospitalization duration of 2 (IQR, 2–3) days. Intraoperative complications occurred in 4.7% of cases, while postoperative complications arose in 15.6%, including elevated creatinine (3.1%) and infections (10.9%). The 30-day SFR was 84.4%, with no significant differences observed between UAS positioning groups (Table 2).

Outcomes results according to ureteral sheath position

Table 2 summarizes continuous outcome measures stratified by ureteral sheath placement location. The 30-day SFR was 83.8% for the juxta-pelvic junction group and 85.2% for the distal/proximal ureter group, with no statistically significant difference (P=0.86).

As detailed in Table 3, intraoperative complications occurred in 5.4% of juxta-pelvic sheath cases (2 instances of pelvicalyceal bleeding) vs. 3.7% of ureteral placements (1 ureteral injury necessitating stenting), with no significant difference (P=0.75). Postoperative creatinine elevation was observed in 2.7% and 3.7% of the respective groups (P=0.82). Infection rates were 10.81% (Group A) and 11.11% (Group B) (P=0.96), while overall postoperative complications occurred in 16.2% and 18.5% of cases (P=0.67). Excluding mild haematuria, 80% of complications were Clavien-Dindo grade I or II. Only one case per group required intervention for ureteral stent migration (Clavien-Dindo ≥ III), both managed by stent repositioning (P=0.82) (Table 3). The 30-day SFR showed no significant difference between groups [83.8% vs. 85.2%, risk ratio =0.98; 95% confidence interval (CI): 0.84–1.14], as shown in Table 3.

The median operative time—defined as the interval from anaesthesia induction to ureteral stent placement—differed minimally between the juxta-pelvic and intra-ureteral groups [75 (IQR, 61–88) vs. 74 (IQR, 52–94) min; Cohen’s d=0.07; 95% CI: −0.33 to 0.47]. The difference in hospital stays [2 (IQR, 2–3) vs. 2 (IQR, 2–4) days] yielded a negligible effect size (Cohen’s d=0.10; 95% CI: −0.29 to 0.49; P=0.45).

Discussion

Our study demonstrates that UAS positioning—whether juxta-pelvic or distal/proximal ureteral—does not significantly influence operative time, hospitalization duration, complication rates, or short-term stone-free outcomes in patients undergoing fURS for renal calculi. These findings contribute to the growing body of literature examining the role of UAS in modern endourology, where its use has become routine despite persistent debates regarding optimal placement and clinical impact. The evolution of UAS technology since its introduction in 1974 (21) has been marked by significant advancements in design, including hydrophilic coatings and hub-locking mechanisms (22), which have improved safety and procedural efficiency. Contemporary research has focused on refining UAS applications, such as evaluating the necessity of preoperative stenting, comparing outcomes across sheath models, and investigating fluid dynamics during fURS. For instance, Assantachai et al. (23) found no statistically significant differences in SFRs or complications between patients with and without preoperative stenting, though trends suggested potential benefits for presenting at longer follow-ups. Similarly, Damar et al. (24) reported comparable SFR and complication rates with or without UAS, though postoperative pain scores were marginally lower in the UAS group, hinting at patient-centred advantages. The mechanical properties of UAS models further complicate decision-making. Patel and Monga’s (7) comparative analysis highlighted trade-offs between safety, lubricity, and radio-opacity among commercial sheaths, with the Boston Scientific Navigator HD exhibiting superior performance in several domains. Such variability underscores the need for individualized device selection based on procedural requirements. Crucially, the hydrodynamic effects of UAS positioning remain a key consideration. Faria-Costa et al. (25) demonstrated that mid-ureteral placement and larger sheath sizes enhance irrigation outflow in specific calyces, which may optimize stone clearance during high-power laser lithotripsy. Complementary computational modelling by Tammaro et al. (26) suggested that aligning the UAS tip with the ureteroscope tip improves fragment evacuation, reinforcing the importance of technical precision. Despite these insights, our study found no outcome disparities based on UAS location, suggesting that surgeons may prioritize anatomical constraints (e.g., strictures) or operative comfort over idealized positioning. However, this conclusion must be contextualized within the study’s limitations. In this retrospective study, the positioning of the UAS was determined intraoperatively based on feasibility factors such as ureteral compliance, introducing an inherent potential for selection bias due to the non-randomized nature of this decision-making process. Consequently, while the Resorlu-Unsal stone score (27) has been externally validated as a reliable predictor of RIRS outcomes, existing scoring systems do not consider UAS positioning as a variable. Our findings, therefore, suggest that this parameter may warrant inclusion in future iterations of such predictive models, particularly if larger, prospective investigations substantiate its clinical significance. Nonetheless, the retrospective design and lack of randomization in our study limit causal inference and underscore the need for further validation through rigorously controlled research. The modest sample size (n=64) and the single-centre, single-surgeon design may limit the generalizability and statistical power of the findings—particularly regarding less frequent outcomes such as complications—although the latter also serves to minimize surgeon-related confounding. Furthermore, the short 30-day follow-up period, combined with the exclusion of previously treated patients, precludes a comprehensive evaluation of long-term functional outcomes and comparative efficacy, and prevents an adequate assessment of late complications such as ureteral strictures. The declining use of conventional UAS in favor of suction devices is an important trend; nevertheless, our findings remain pertinent to daily practice where standard UAS continue to be extensively employed.

Conclusions

In summary, our results suggest that UAS positioning—whether juxta-pelvic or ureteral—does not significantly alter perioperative outcomes, complication rates, or short-term stone-free status in fURS for renal stones. This supports the notion that surgeons may adapt sheath placement to individual patient anatomy without compromising safety or efficacy. Nevertheless, the retrospective nature of this study necessitates cautious interpretation, as unmeasured confounders and selection bias may influence observations. Future prospective studies with larger cohorts, standardized UAS protocols, and extended follow-up are warranted to validate these findings and explore subtler advantages of specific placements (e.g., pain reduction, long-term ureteral patency). Additionally, cost-effectiveness analyses and patient-reported outcome measures could further refine clinical guidelines. Until then, UAS use should remain guided by surgeon expertise, patient-specific factors, and ongoing technological advancements in endourology.

Acknowledgments

We extend our sincere gratitude to Dr. L. Farina for her invaluable intraoperative assistance for each surgical procedure. We also wish to thank Dr. M. Campanaro for her meticulous work in reviewing text and tables, as well as for her contributions to document layout.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://asj.amegroups.com/article/view/10.21037/asj-25-54/rc

Data Sharing Statement: Available at https://asj.amegroups.com/article/view/10.21037/asj-25-54/dss

Peer Review File: Available at https://asj.amegroups.com/article/view/10.21037/asj-25-54/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://asj.amegroups.com/article/view/10.21037/asj-25-54/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by our Local Institutional Review Board A.O.U. Federico II – A.O.R.N. Cardarelli (ID-312015) and informed consent was taken from all individual participants for the inclusion of their data in the database and for their use for scientific research purposes.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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