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.