This multicenter, randomized, controlled superiority trial (the SCULPT trial) aims to compare the efficacy and safety of a novel steerable flexible and navigable suction ureteral access sheath (FANS) versus the conventional FANS in the treatment of lower pole renal stones ≤2 cm. Lower pole stones are particularly challenging due to the narrow infundibular-pelvic anatomy that limits the maneuverability of standard FANS. The steerable FANS incorporates an active deflection mechanism that allows for independent control, potentially improving the success rate of accessing the lower pole calyx, performing laser lithotripsy, and aspirating stone fragments without additional adjuncts.

A total of 400 patients from 20 high-volume urological centers in China (approximately 20 patients per center) will be randomized in a 1:1 ratio to receive either steerable FANS or conventional FANS during flexible ureteroscopy. Primary outcome measures include the success rate of FANS navigation into the lower pole calyx as evidenced by direct stone visualization, effective laser lithotripsy, and successful stone aspiration. Secondary outcomes will assess immediate and 1-month stone-free rates, operative time, complication rates, instrument durability, and improvements in quality of life. This study is expected to provide critical evidence to guide clinical decision-making and potentially improve treatment efficiency for challenging lower pole renal stones.

This trial is designed in response to the current challenges faced in the management of lower pole renal stones using flexible ureteroscopy, particularly when using conventional FANS. The narrow calyceal angles and complex lower pole anatomy can impede the passage of the access sheath, thereby limiting the efficiency of stone fragmentation and clearance. The innovative steerable FANS overcomes these limitations by offering an independent, active deflection mechanism that facilitates a greater range of movement, thus optimizing the access to lower pole calyces.

Background and Objectives Lower pole stones are notoriously difficult to treat due to their anatomical position and the limited maneuverability of conventional ureteral access sheaths. The new steerable FANS, with its deflection lever at the distal handle, allows for active, independent adjustment under endoscopic guidance, which may result in a higher success rate of reaching the lower pole and more efficient stone clearance. The primary objective of this trial is to compare the success rate of FANS navigation into the lower pole renal calyx between the steerable and conventional devices. Secondary objectives include the evaluation of immediate (within 24 hours) and 1-month stone-free rates, operative time, length of hospital stay, usage of auxiliary devices (e.g., stone baskets), instrument damage rates, complication rates (graded by the Clavien-Dindo system), and the impact on patient quality of life (assessed via the Wisconsin Stone QoL questionnaire).

Study Design and Methods

Trial Type:

This is a multicenter, prospective, single-blind, superiority, randomized controlled trial.

Study Setting and Participants:

The study will be conducted at 20 high-volume urological centers across China, with each center recruiting approximately 20 patients. Eligible participants are adults aged 18-75 years, diagnosed with a single lower pole renal stone ≤2 cm (confirmed by CT) and who meet all inclusion and exclusion criteria.

Randomization and Group Allocation:

A centralized, stratified randomization process (1:1 ratio) will allocate patients to either the steerable FANS or conventional FANS group. Random sequences will be generated electronically using permuted blocks within each center to maintain allocation concealment.

Interventions:

All patients will undergo flexible ureteroscopy under general anesthesia with standardized use of 7.5 Fr digital flexible ureteroscopes. Preoperative imaging (contrast-enhanced CT urography) will assess stone size, location, and anatomical parameters. Depending on ureteral diameter, an appropriate FANS (either 11/13 Fr or a smaller version) will be selected. Laser lithotripsy will be performed using a 200 µm laser fiber (energy settings ≤30 W) alongside continuous negative-pressure suction to aspirate stone fragments. If the sheath cannot be navigated into the lower pole due to anatomical constraints, an adjunct stone basket may be employed.

Outcome Measures:

Primary Outcome:

The success rate of FANS navigation into the lower pole calyx, defined as the sheath reaching the calyx, performing effective laser lithotripsy, and aspirating stone fragments without additional adjuncts.

Secondary Outcomes:

These include the immediate (24-hour) and final (1-month) stone-free rates (defined as no residual stone or fragments >2 mm on CT), operative time, duration of hospital stay, intraoperative usage of adjunct devices, damage rates of the ureteroscope and FANS, complications within one month (graded by Clavien-Dindo), and quality of life improvements as measured by the Wisconsin Stone QoL questionnaire.

Follow-up and Data Collection:

Patients will undergo a low-dose CT scan within 24 hours postoperatively to assess the immediate stone-free status, with a follow-up CT at 1 month for final assessment. Clinical data, including operative details and follow-up results, will be recorded in standardized case report forms (CRFs) at each center. This will ensure consistency and completeness of data across the multicenter trial.

Sample Size and Statistical Analysis:

Based on preliminary data showing a 60% success rate with conventional FANS and an anticipated 80% with the steerable FANS, with a superiority margin of 6%, a total of 400 participants (200 per group) has been calculated to achieve 80% power at a one-sided α of 2.5%, accounting for potential dropouts. Statistical analyses will be conducted using SPSS software, with continuous variables analyzed via t-tests or Mann-Whitney U tests (depending on data distribution) and categorical variables assessed using chi-square or Fisher's exact tests. Multivariate analyses will be performed where necessary, and results will be presented with 95% confidence intervals.

Quality Control and Safety Monitoring:

All participating centers will undergo standardized training to ensure uniformity in surgical procedures and data collection. Monthly monitoring visits will verify protocol adherence and data integrity. Any adverse events will be meticulously recorded and reported promptly to the Ethics Committee, with regular cumulative safety reviews performed by the principal investigator.

Significance and Expected Outcomes This trial is the first head-to-head comparison of steerable versus conventional FANS in the management of lower pole renal stones. If the steerable FANS demonstrates superiority in navigating the lower pole and enhancing stone clearance efficiency, it could transform the current endourological approach to challenging renal calculi. In addition, the comprehensive evaluation of instrument durability and complication profiles will aid in economic assessments and inform patient counseling regarding procedural risks and benefits. Ultimately, the findings of this study are expected to contribute robust evidence toward optimizing clinical strategies, improving patient outcomes, and potentially expanding the indications for flexible ureteroscopy in complex renal stone management.

Inclusion Criteria:

• Adults aged 18-75 years
• Diagnosed with a single lower pole renal stone ≤2 cm by CT
• American Society of Anesthesiology (ASA) score of 1-3
• Ability to provide written informed consent
• Willingness and ability to comply with trial procedures and follow-up

Exclusion Criteria:

• Patients with urinary tract anatomical abnormalities (e.g., horseshoe kidney, ileal conduit)
• Untreated urinary tract infection
• Presence of multiple stones or stones located outside the lower pole
• Absolute contraindications to flexible ureteroscopy
• Inability to understand or complete trial documentation