Comparison of the efficacy and safety of flexible vacuum-assisted ureteral access sheath–assisted flexible ureteroscopic lithotripsy, conventional ureteral access sheath–assisted flexible ureteroscopic lithotripsy, and mini-percutaneous nephrolithotomy for 2–3 cm renal stones

Abstract

Background:

The optimal management of 2–3 cm renal stones remains challenging because effective stone clearance must be balanced against perioperative morbidity. Mini-percutaneous nephrolithotomy (mPCNL) provides high stone-free rates (SFR) but is associated with greater procedural burden, whereas flexible ureteroscopic lithotripsy (fURL) is less invasive but may be limited by fragment clearance efficiency. A flexible vacuum-assisted ureteral access sheath (FV-UAS) has recently been introduced to facilitate fragment evacuation and improve intrarenal drainage during fURL.

Objectives:

To compare the efficacy and safety of FV-UAS–assisted fURL, conventional ureteral access sheath–assisted flexible ureteroscopic lithotripsy (UAS–assisted fURL), and mPCNL for the treatment of 2–3 cm renal stones, and to provide evidence for surgical decision-making in this clinical setting.

Design:

This was a retrospective single-center comparative study.

Methods:

This retrospective study included 156 patients with 2–3 cm renal stones who underwent FV-UAS–assisted fURL (FV-UAS group, n = 50), UAS–assisted fURL (UAS group, n = 54), or mPCNL (mPCNL group, n = 52) at Xi’an People’s Hospital between June 2022 and December 2024. Perioperative outcomes were compared, including operative time, postoperative hemoglobin decrease, postoperative pain assessed by the visual analogue scale (VAS), postoperative length of hospital stay, total hospitalization costs, and postoperative adverse events, including fever, renal colic, urinary tract infection, and steinstrasse. SFR was assessed on postoperative day 3 and at 1 month postoperatively.

Results:

Operative time differed significantly among the three groups (FV-UAS 77.56 ± 15.04 min vs mPCNL 67.60 ± 10.44 min vs UAS 85.04 ± 15.78 min; p < 0.05). Postoperative hemoglobin decrease was significantly lower in the FV-UAS and UAS groups than in the mPCNL group (3.50 ± 2.40 g/L and 4.01 ± 2.14 g/L vs 13.86 ± 3.21 g/L; p < 0.001). The postoperative length of stay was shorter in the FV-UAS group than in the UAS group and markedly shorter than in the mPCNL group (3.04 ± 0.73 d vs 3.52 ± 0.72 d vs 6.04 ± 0.86 d; p < 0.05). Postoperative VAS scores were lower in the FV-UAS and UAS groups than in the mPCNL group (p < 0.05), with no significant difference between the two fURL groups. Regarding total hospitalization costs, the mPCNL group had the lowest costs, and the FV-UAS group had lower costs than the UAS group (p < 0.05). The overall adverse event rates were comparable among groups. Steinstrasse occurred in three cases, all in the UAS group. On postoperative day 3, SFRs were 94.0% (FV-UAS), 75.9% (UAS), and 80.8% (mPCNL), with the FV-UAS group higher than the UAS group (p < 0.05). At 1 month, SFRs were 96.0% (FV-UAS), 81.5% (UAS), and 96.2% (mPCNL), with both the FV-UAS and mPCNL groups higher than the UAS group (p < 0.05).

Conclusion:

For 2–3 cm renal stones, FV-UAS–assisted fURL was associated with less hemoglobin decrease, lower postoperative pain, and shorter hospital stay than mPCNL, and showed advantages over UAS–assisted fURL in operative time and hospitalization costs, while achieving a 1-month SFR comparable to mPCNL. FV-UAS–assisted fURL may represent a safe and effective minimally invasive alternative for 2–3 cm renal stones.

Trial registration:

Not applicable.

Plain language summary

A less invasive option for 2–3 cm kidney stones: comparing three common procedures for stone removal

Kidney stones that are 2–3 cm in size can be difficult to treat. Several minimally invasive procedures are used, but it is not always clear which option offers the best balance of effectiveness, comfort, and safety. We compared three approaches: (1) flexible ureteroscopy using a new “vacuum-assisted” tube to help remove stone fragments, (2) flexible ureteroscopy using a standard tube, and (3) mini-percutaneous nephrolithotomy, which removes stones through a small channel created through the skin into the kidney. We reviewed 156 patients treated at Xi’an People’s Hospital from June 2022 to December 2024. We compared operation time, blood loss (measured by hemoglobin drop), pain after surgery, length of hospital stay, total hospital costs, complications, and how often patients were stone-free shortly after surgery and at 1 month. All three methods were generally safe, with similar overall complication rates. The mini-percutaneous approach had more bleeding-related burden and longer hospital stay, and patients reported higher pain. The vacuum-assisted ureteroscopy group had the shortest hospital stay and less bleeding-related burden than the mini-percutaneous group. It also achieved a higher early stone-free rate than standard ureteroscopy. At 1 month, the vacuum-assisted ureteroscopy group reached a stone-free rate comparable to the mini-percutaneous approach and higher than standard ureteroscopy. A temporary blockage by stone fragments occurred only in the standard ureteroscopy group. Overall, vacuum-assisted ureteroscopy may be a safe and effective minimally invasive alternative for medium-sized kidney stones, with quicker recovery and good stone clearance.

Introduction

For the management of 2–3 cm renal stones, the relatively large stone burden and potentially complex location predispose patients to urinary obstruction, infection, and other serious complications, which can substantially impair quality of life and overall health.^1,2 Therefore, an accurate and minimally invasive surgical strategy is often required to achieve effective stone clearance. With advances in minimally invasive techniques, flexible ureteroscopic lithotripsy (fURL) and percutaneous nephrolithotomy (PCNL) have become the mainstay approaches for renal stone treatment. Mini-percutaneous nephrolithotomy (mini-PCNL), an effective option for larger or complex renal stones, is widely accepted and utilized because of its high stone-free rate (SFR); however, it is still associated with a relatively higher risk of complications, including significant bleeding related to tract dilation, postoperative flank pain, and potential visceral injury. ³

In recent years, improvements in flexible ureteroscopy and laser lithotripsy have shown considerable potential for stones >2 cm, particularly for 2–3 cm renal stones. This approach may reduce surgical invasiveness by avoiding percutaneous access; the intraoperative use of adjunctive devices such as stone baskets can further improve SFR.^4–6 For patients seeking a less invasive option despite a large stone burden, staged procedures may also achieve satisfactory SFR.^7,8 Nevertheless, although conventional ureteral access sheath (UAS)–assisted fURL has been widely adopted, elevated intrarenal pressure (IRP) and a higher burden of residual fragments (RF) remain two major limitations of ureteroscopic lithotripsy, ⁹ which may compromise clearance efficiency and adaptability to complex intrarenal anatomy.

More recently, a flexible vacuum-assisted ureteral access sheath (FV-UAS) has been introduced into fURL. Because its distal tip can passively bend with the rotation of the flexible ureteroscope and reach different calyces, FV-UAS may effectively reduce IRP, decrease postoperative infectious complications, and actively aspirate stone fragments, thereby improving SFR. ¹⁰ However, the optimal surgical strategy that maximizes stone clearance while minimizing complications for 2–3 cm renal stones remains to be determined. Therefore, this study aimed to compare the efficacy and safety of FV-UAS–assisted fURL, conventional UAS–assisted fURL, and mini-PCNL in the treatment of 2–3 cm renal stones, with the goal of providing evidence to optimize surgical decision-making for 2–3 cm renal stone disease.^11,12

Materials and methods

The reporting of this retrospective study conforms to the STROBE statement (Supplemental Material). ¹³

Clinical data

We retrospectively collected data from patients with 2–3 cm renal stones who underwent one of the three surgical approaches at Xi’an People’s Hospital between June 2022 and December 2024. A total of 156 patients were included and allocated into three groups according to the procedure performed: the FV-UAS group (n = 50), who underwent FV-UAS–assisted fURL; the UAS group (n = 54), who underwent conventional UAS–assisted fURL; and the mini-percutaneous nephrolithotomy (mPCNL) group (n = 52), who underwent mPCNL. Written informed consent was obtained from all patients prior to surgery. The study protocol was approved by the Medical Ethics Committee of the hospital.

Inclusion criteria were as follows:

• (1) a diagnosis of 2–3 cm renal stones confirmed by imaging;

• (2) fulfillment of surgical indications and willingness to undergo fURL or mPCNL;

• (3) age 18–75 years;

• (4) preserved renal function and suitability for anesthesia.

Patients older than 75 years were excluded to reduce age-related heterogeneity and perioperative risk, thereby improving comparability among the three treatment groups.

Exclusion criteria were as follows:

• (1) severe cardiopulmonary dysfunction or other systemic diseases contraindicating surgery;

• (2) coagulation disorders precluding safe surgery;

• (3) pregnancy or lactation;

• (4) congenital urinary tract malformations or other anatomical abnormalities precluding standard endourological access, or stones located in sites inaccessible to the surgical instruments;

• (5) other urological diseases that could confound outcome assessment during the study period (e.g., urinary tract malignancy). The study flow diagram is shown in Figure 4.

Figure 4.

Study flow diagram of patient selection, grouping, follow-up, and outcome assessment.

fURL, flexible ureteroscopic lithotripsy; FV-UAS, flexible vacuum-assisted ureteral access sheath; KUB, kidney–ureter–bladder radiography; mPCNL, mini-percutaneous nephrolithotomy; POD, postoperative day; UAS, ureteral access sheath; VAS, visual analogue scale.

Sample size calculation

No formal prospective sample size calculation was performed because of the retrospective design of this study. The sample size was determined by the number of eligible consecutive patients with 2–3 cm renal stones who underwent FV-UAS–assisted fURL, UAS–assisted fURL, or mPCNL at our institution between June 2022 and December 2024.

Surgical procedures

Perioperative antibiotic strategy and surgeon

Preoperative antibiotic use was determined based on urinalysis, procalcitonin, C-reactive protein, and midstream urine culture results. In patients with urinary tract infection, culture-directed antibiotics were administered until urinalysis returned to normal or near-normal. When susceptibility results were unavailable preoperatively, empirical broad-spectrum antibiotics were prescribed. All patients received a prophylactic broad-spectrum antibiotic injection 30 min before surgery, primarily targeting Gram-negative bacteria. All procedures were performed by the same associate chief physician, who had experience with more than 15,000 stone surgeries, including PCNL, flexible ureteroscopic lithotripsy, and rigid ureteroscopic lithotripsy. In both the FV-UAS and UAS groups, 12/14-Fr ureteral access sheaths manufactured by Cooper were used; the sheath length was 35 cm in female patients and 45 cm in male patients. A 7.5-Fr flexible ureteroscope from the same manufacturer was used in both groups.

Preoperative ureteral stenting in fURL groups

A subset of patients in the FV-UAS–assisted fURL and UAS–assisted fURL groups had a ureteral stent placed preoperatively. Indications included: (1) a history of ureteral stricture or suspected ureteral stricture on computed tomography; and (2) obstructing stones complicated by acute pyelonephritis, for which ureteral stenting was performed first for drainage. In this study, a history of ureteral stricture or suspected ureteral narrowing on preoperative imaging was not classified as a urinary tract malformation. The term “urinary tract malformations” in the exclusion criteria referred to congenital or fixed anatomical abnormalities that substantially altered the urinary tract anatomy or prevented standard endourological access.

FV-UAS–assisted fURL

Patients were placed in the lithotomy position under general anesthesia. After routine skin preparation and draping, a rigid ureteroscope (STORZ, F8/9.8) was introduced into the bladder to identify both ureteral orifices. In patients with a pre-existing double-J (D-J) stent, the stent was removed with ureteral forceps. A zebra guidewire was then advanced into the affected ureter. The rigid ureteroscope was advanced over the guidewire to inspect the ureter for stricture, malformation, or other abnormalities, and the zebra guidewire was left in situ. Under guidewire guidance, a 12/14-Fr flexible vacuum-assisted ureteral access sheath (FV-UAS; Figure 1) was inserted and connected to a central negative-pressure suction system (−25 to −30 kPa). A flexible ureteroscope was advanced through the sheath into the renal pelvis, and the collecting system was systematically inspected. Holmium:YAG laser lithotripsy (0.8–1.5 J, 10–30 Hz) was used to dust the stones. Simultaneously, the sheath was positioned near residual fragments to facilitate active aspiration. After confirming the absence of obvious residual stones in the renal pelvis and calyces, a 6-F D-J stent was placed in all patients at the end of the procedure.

Figure 1.

Intraoperative view of flexible vacuum-assisted ureteral access sheath–assisted flexible ureteroscopic lithotripsy.

UAS–assisted fURL

Patients were placed in the lithotomy position under general anesthesia, followed by standard skin preparation and draping. A rigid ureteroscope (STORZ, F8/9.8) was introduced into the bladder to identify both ureteral orifices. In patients with a pre-existing D-J stent, the stent was removed with ureteral forceps. A zebra guidewire was advanced into the affected ureter, and the rigid ureteroscope was advanced over the guidewire to evaluate the ureter for stricture or malformation. The zebra guidewire was left in situ. Under guidewire guidance, a 12/14-Fr conventional ureteral access sheath (UAS; Figure 2) was inserted. A flexible ureteroscope was advanced through the sheath into the kidney. Holmium:YAG laser lithotripsy (0.8–1.5 J, 10–30 Hz) was performed, and a stone basket was used to retrieve larger residual fragments. After confirming no obvious residual stones in the renal pelvis and calyces, a 6-F D-J stent was placed in all patients at the end of the procedure.

Figure 2.

Intraoperative view of conventional ureteral access sheath–assisted flexible ureteroscopic lithotripsy.

Mini-percutaneous nephrolithotomy

Patients were initially placed in the lithotomy position under general anesthesia and underwent routine skin preparation and draping. A rigid ureteroscope was used to place a ureteral catheter on the affected side up to the renal pelvis. The patient was then repositioned to the prone position (Figure 3). Normal saline was infused retrogradely through the ureteral catheter to create artificial hydronephrosis. Ultrasound was used to assess hydronephrosis and the relationship between the kidney and surrounding organs. After selecting the target calyx, the puncture tract was most commonly established through the posterior middle calyx or the fornix of the lower calyx. Under ultrasound guidance, renal puncture was performed following the principle of “prefer shallow over deep.” Once urine efflux was observed, a metallic J-shaped guidewire was inserted. Sequential fascial dilators were then used to dilate the tract to 16–18 F, and a peel-away sheath was placed to establish the working channel. A 9.8 F nephroscope or short ureteroscope was introduced through the tract. Under irrigation via an infusion pump, holmium:YAG laser lithotripsy (0.8–1.5 J, 10–30 Hz) was used to fragment the stones, and fragments were evacuated by water pressure. The renal calyces, renal pelvis, and proximal ureter were inspected for residual stones. At the end of the procedure, a 6 F D-J stent and a nephrostomy tube were placed. Postoperatively, anti-infective therapy was continued as indicated, and patients were closely monitored.

Figure 3.

Intraoperative view of mini-percutaneous nephrolithotomy.

Study variables and follow-up

We reviewed outpatient records, imaging data, and stone composition analysis reports. Baseline demographic characteristics (sex, age, laterality) and preoperative variables were collected. Comorbidities were defined as the presence of one or more pre-existing chronic diseases, such as hypertension, diabetes mellitus, coronary artery disease, or cerebrovascular disease; no standardized comorbidity index was used. All patients underwent routine preoperative laboratory evaluation, including complete blood count, urinalysis, procalcitonin, C-reactive protein, renal function tests, and urine culture. Imaging assessment included kidney–ureter–bladder radiography (KUB) and non-contrast computed tomography (NCCT) of the urinary tract to evaluate hydronephrosis and stone-related parameters, including stone size, location, number, CT attenuation value (Hounsfield units), and the infundibulopelvic angle (IPA).

Intraoperative and postoperative variables included operative time; postoperative serum creatinine, hemoglobin, white blood cell count, C-reactive protein, and procalcitonin; postoperative length of hospital stay; and total hospitalization costs. Operative time was defined as the interval from ureteroscope insertion to scope removal at the end of the procedure. Total hospitalization costs were calculated as the sum of surgical fees, anesthesia fees, bed charges, medication costs, examination costs, consumable material costs, and nursing fees. KUB was repeated on postoperative day 1, postoperative day 3, and 1 month postoperatively to assess the SFR. Stone-free status was defined as no residual stones or residual fragments <4 mm in diameter. The occurrence of steinstrasse was recorded.

Postoperative pain on postoperative day 1 was evaluated using the visual analogue scale (VAS; range 0–10), with higher scores indicating greater pain intensity. Postoperative adverse events, including fever, renal colic, urinary tract infection, and steinstrasse, were recorded and compared among the three groups. For each event, the type, timing, and management were documented to objectively compare the safety profiles of the three surgical approaches.

Statistical analysis

All statistical analyses were performed using SPSS Statistics version 25.0 (IBM Corp., Armonk, NY, USA). Continuous variables were tested for normality. Normally distributed data are presented as mean ± standard deviation (SD). Comparisons among the three groups were performed using one-way analysis of variance (ANOVA); when significant, pairwise comparisons were conducted using Student’s t-tests. Categorical variables are presented as numbers (percentages) and were compared using the chi-square test or Fisher’s exact test, as appropriate based on expected cell counts. A two-sided p value < 0.05 was considered statistically significant.

Results

Baseline characteristics

No significant differences were observed among the three groups with respect to age, sex, stone location, comorbidities, use of anticoagulant therapy, positive urine culture, involvement of the lower calyx, degree of hydronephrosis, stone attenuation on CT (Hounsfield units), IPA, or maximal stone diameter (all p > 0.05; Table 1).

Table 1.

Clinical characteristics of participants.

Variable	FV-UAS group (n = 50)	UAS group (n = 54)	mPCNL group (n = 52)	F/c2	p Value
Age (years)/(Mean ± SD)	49.62 ± 9.89	48.96 ± 10.89	47.81 ± 9.95	0.409	0.665
Gender/n (%)
Male	29 (58.00)	24 (44.44)	27 (51.92)	1.920	0.382
Female	21 (42.00)	30 (55.56)	25 (48.08)
Stone position/n (%)
Left	24 (48.00)	26 (48.15)	26 (50.00)	0.052	0.975
Right	26 (52.00)	28 (51.85)	26 (50.00)
Comorbidities/n (%)	10 (20.00)	11 (20.37)	9 (17.31)	0.188	0.910
Anticoagulant use/n (%)	2 (4.00)	3 (5.56)	1 (1.92)	0.95	0.622
Positive urine culture/n (%)	7 (14.00)	6 (11.11)	6 (11.54)	0.233	0.890
Involvement of the lower calyx of the kidney/n (%)	20 (40.00)	20 (37.04)	21 (40.28)	0.150	0.928
IPA/(Mean ± SD)	47.24 ± 5.53	48.57 ± 5.19	46.63 ± 4.82	0.330	0.701
Hydronephrosis
Mild/n (%)	29 (52.00)	26 (53.70)	13 (25.00)	8.46	0.076
Moderate/n (%)	13 (32.00)	16 (24.07)	29 (55.77)
Gross/n (%)	3 (10.00)	5 (5.56)	5 (9.62)
Long axis of the stone (cm)/(Mean ± SD)	2.52 ± 0.29	2.53 ± 0.29	2.67 ± 0.22	0.08	0.089
CT value of the stone/(Mean ± SD)	933.32 ± 144.74	915.07 ± 154.72	955.04 ± 123.30	1.06	0.35

FV-UAS, flexible vacuum-assisted ureteral access sheath; IPA, infundibulopelvic angle; mPCNL, mini-percutaneous nephrolithotomy.

Comparison of intraoperative and postoperative outcomes

Intraoperative and postoperative outcomes are summarized in Table 2. Operative time differed significantly among the three groups (FV-UAS 77.56 ± 15.04 min, mPCNL 67.60 ± 10.44 min, and UAS 85.04 ± 15.78 min; p < 0.05), with the shortest operative time observed in the mPCNL group.

Table 2.

Comparison of intraoperative and postoperative data among patients.

Parameter/(mean ± SD)	FV-UAS group (n = 50)	UAS group (n = 54)	mPCNL group (n = 52)	F/c2	p Value
Operation time (min)	77.56 ± 15.04	85.04 ± 15.78 a	67.60 ± 10.44 a b	20.77	<0.05*
Decline in Hb levels (g/l)	3.5 ± 2.40	4.0 ± 2.14	13.86 ± 3.21 a b	257.72	<0.05*
Postoperative day 1 PCT (ng/ml)	0.095 ± 0.071	0.108 ± 0.124	0.114 ± 0.119	0.395	0.675
CRP	11.72 ± 10.16	13.20 ± 10.85	14.27 ± 11.05	0.728	0.484
Postoperative length of hospital stay (d)	3.04 ± 0.73	3.52 ± 0.72 a	6.04 ± 0.86 a b	224.59	<0.05*
VAS day 1	2.38 ± 1.41	2.93 ± 1.43	5.04 ± 1.24 a b	54.87	<0.05*
Total hospitalization cost (CNY)	19776.32 ± 862.48	21791.15 ± 1143.86 a	17052.48 ± 671.76 a b	355.21	<0.05*

Statistical comparisons: ^avs FV-UAS group, p < 0.05; ^bvs UAS group, p < 0.05.

^*p Value is significant.

CRP, C-reactive Protein; d, days; FV-UAS, flexible vacuum-assisted ureteral access sheath; Hb, hemoglobin; mPCNL, mini-percutaneous nephrolithotomy; PCT, Procalcitonin; VAS, Visual Analogue Scale.

Postoperative hemoglobin decrease was significantly lower in the FV-UAS and UAS groups than in the mPCNL group (3.50 ± 2.40 g/L and 4.01 ± 2.14 g/L vs 13.86 ± 3.21 g/L; p < 0.001).

On postoperative day 1, procalcitonin and C-reactive protein levels were comparable among the three groups (both p > 0.05). The postoperative length of hospital stay was significantly shorter in the FV-UAS group than in the UAS group and markedly shorter than in the mPCNL group (3.04 ± 0.73 d vs 3.52 ± 0.72 d vs 6.04 ± 0.86 d; p < 0.05).

Postoperative day 1 pain assessed by VAS was lower in the FV-UAS and UAS groups than in the mPCNL group (2.38 ± 1.41 and 2.93 ± 1.43 vs 5.04 ± 1.24; p < 0.05), with no significant difference between the two fURL groups (p > 0.05).

Total hospitalization costs differed among groups (FV-UAS 19,776.32 ± 862.48, mPCNL 17,052.48 ± 671.76, and UAS 21,791.15 ± 1143.86; p < 0.05).

Comparison of SFR

On postoperative day 3, the SFR in the mPCNL group was not significantly different from that in either fURL group. However, the FV-UAS group achieved a higher SFR than the UAS group (94.0% vs 75.9%; p < 0.05). Stone-free rates on postoperative day 3 and at 1 month are summarized in Table 3.

Table 3.

Assessment of postoperative SFRs.

Parameter/n (%)	FV-UAS group (n = 50)	UAS group (n = 54)	mPCNL group (n = 52)	F/c2	p Value
Postoperative day 3 SFR	47 (94.0)	41 (75.9) a	42 (80.8)	6.40	<0.05*
Postoperative day 30 SFR	48 (96.0)	44 (81.5) a	50 (96.2) b	9.21	<0.05*

Statistical comparisons: ^avs FV-UAS group, p < 0.05; ^bvs UAS group, p < 0.05.

^*p Value is significant.

FV-UAS, flexible vacuum-assisted ureteral access sheath; mPCNL, mini-percutaneous nephrolithotomy; SFR, Stone-Free Rate; VAS, Visual Analogue Scale.

At 1 month postoperatively, the SFR remained higher in the FV-UAS group than in the UAS group (96.0% vs 81.5%) and was comparable to that in the mPCNL group (96.2%; p < 0.05).

Comparison of postoperative adverse events

Postoperative adverse events are summarized in Table 4. In the FV-UAS group, fever occurred in one patient (2.0%), renal colic in five patients (10.0%), and urinary tract infection (UTI) in one patient (2.0%). In the UAS group, fever occurred in five patients (9.26%), renal colic in five patients (9.26%), and UTI in three patients (5.56%). In the mPCNL group, fever occurred in three patients (5.77%), renal colic in eight patients (15.38%), and UTI in three patients (5.77%). There were no statistically significant differences in these adverse event rates among the three groups (p > 0.05). All reported adverse events were minor and were managed conservatively with symptomatic and/or supportive treatment; no patient required reoperation, ICU admission, or readmission. Steinstrasse was not observed in the FV-UAS or mPCNL groups, whereas three cases occurred in the UAS group.

Table 4.

Comparison of postoperative adverse events.

Parameter/n (%)	FV-UAS group (n = 50)	UAS group (n = 54)	mPCNL group (n = 52)	c 2	p Value
Fever
No	49 (98.0)	49 (90.74)	49 (94.23)	2.52	0.284
Yes	1 (2.0)	5 (9.26)	3 (5.77)
Renal colic
No	45 (90.0)	49 (90.74)	44 (84.62)	1.14	0.564
Yes	5 (10.0)	5 (9.26)	8 (15.38)
UTI
No	49 (98.00)	51 (94.44)	49 (94.23)	1.06	0.587
Yes	1 (2.00)	3 (5.56)	3 (5.77)
Stone street	0	3 (5.56)	0	5.78	0.056

FV-UAS, flexible vacuum-assisted ureteral access sheath; mPCNL, mini-percutaneous nephrolithotomy; UTI, urinary tract infection.

Discussion

In this retrospective study, FV-UAS–assisted fURL demonstrated a favorable perioperative profile compared with both conventional UAS–assisted fURL and mPCNL for 2–3 cm renal stones. Specifically, compared with conventional UAS–assisted fURL, FV-UAS–assisted fURL was associated with a shorter operative time, shorter postoperative hospital stay, lower total hospitalization costs, and higher early and 1-month SFRs. Compared with mPCNL, FV-UAS–assisted fURL showed advantages in lower hemoglobin decrease, shorter postoperative hospital stay, and lower postoperative pain scores, while achieving a comparable SFR at 1 month.

These findings suggest that FV-UAS–assisted fURL may offer a useful balance between surgical invasiveness and stone clearance efficiency in selected patients with 2–3 cm renal stones. Compared with conventional UAS–assisted fURL, the vacuum-assisted sheath may facilitate fragment evacuation and improve procedural efficiency, which may contribute to the observed advantages in operative time and stone clearance. ¹⁴ Compared with mPCNL, the absence of a percutaneous tract may partly explain the lower hemoglobin decrease, shorter postoperative stay, and lower pain scores observed in the FV-UAS group. As mPCNL remains an important treatment option for renal stones >2 cm, this comparison is clinically meaningful. ¹⁵

Overall, each approach has distinct strengths: mPCNL provides robust stone clearance but is associated with a relatively higher procedural burden; conventional UAS–assisted fURL is less invasive but may be limited by fragment evacuation efficiency; FV-UAS–assisted fURL may offer a more favorable balance between clearance efficiency and minimal invasiveness.

Regarding operative time, the FV-UAS group had a longer operative time than the mPCNL group but a shorter operative time than the UAS group. This pattern may be related to differences in intrarenal visibility and fragment management. In conventional UAS–assisted fURL, limitations in fragment evacuation and intrarenal drainage under certain conditions may impair visibility and prolong operative manipulation. In contrast, FV-UAS–assisted fURL enables continuous suction-assisted outflow, which can remove turbid irrigation fluid, blood, stone dust, and laser-generated heat, thereby maintaining a clearer operative field, potentially reducing mucosal trauma and improving procedural efficiency. ¹⁶ In addition, the suction setting can be adjusted intraoperatively according to infectious status and collecting system distension, which may facilitate intrarenal drainage and pressure control during the procedure. ¹⁷ From a health-economic perspective, ureteral access sheaths and flexible ureteroscopes are costly and susceptible to damage. ¹⁸ FV-UAS–assisted fURL may reduce the need for consumables such as stone baskets, which could partially explain the lower total hospitalization costs compared with conventional UAS–assisted fURL observed in our cohort.

With respect to postoperative hemoglobin decrease, length of hospital stay, and pain intensity, the FV-UAS group showed more favorable outcomes than the mPCNL group and, to some extent, the UAS group, indicating potential advantages in perioperative recovery and postoperative comfort. Suction-assisted evacuation of irrigation fluid, stone dust, and small fragments may help maintain visibility and procedural efficiency during lithotripsy. Moreover, despite the use of a mini-tract, mPCNL still requires percutaneous access and tract dilation, which may cause renal parenchymal and muscular injury and necessitate longer postoperative bed rest; in contrast, transurethral fURL typically allows earlier ambulation and faster recovery. These differences may also account for the lower postoperative VAS scores in the fURL-based groups compared with the mPCNL group.

SFR is a key indicator of treatment success in renal stone surgery. Previous studies have reported that PCNL may achieve a higher SFR than ureteroscopic lithotripsy for stones >2 cm. ¹⁹ Persistent residual fragments may enlarge over time, promote recurrence, and ultimately lead to reintervention, adversely affecting patients’ physical and psychological well-being as well as quality of life. ²⁰ In our study, the FV-UAS group achieved significantly higher SFRs on postoperative day 3 and at 1 month (94.0% and 96.0%, respectively) than the UAS group (75.9% and 81.5%, respectively), and the 1-month SFR in the FV-UAS group approached that in the mPCNL group (80.8% on day 3 and 96.2% at 1 month). These findings suggest that FV-UAS–assisted fURL can provide effective stone clearance for selected patients with 2–3 cm renal stones. Active suction-assisted evacuation of fragments after lithotripsy may reduce residual stone burden and improve clearance efficiency. By contrast, conventional UAS–assisted fURL does not provide active aspiration, which may partly limit fragment evacuation efficiency and contribute to a greater residual fragment burden.

The incidence of postoperative adverse events is another important endpoint when evaluating procedural safety. A previous study comparing suction ureteral access sheaths versus conventional sheaths for fURL reported lower incidences of postoperative adverse events, including fever (5.5% vs 13.9%), septic shock, and urosepsis (1.8% vs 6.7%), in the suction-sheath group, suggesting a potential advantage of suction-assisted techniques. ²¹ In the present study, the overall rates of postoperative adverse events did not differ significantly among the three groups. Nevertheless, fever and urinary tract infection appeared less frequent in the FV-UAS group (fever 2.0%, UTI 2.0%) than in the UAS group (fever 9.26%, UTI 5.56%), which may be associated with improved irrigation outflow and intrarenal drainage during FV-UAS–assisted fURL. In addition, steinstrasse occurred only in the UAS group, which may reflect less efficient fragment clearance in the absence of active aspiration when managing larger stone burdens.

Several limitations should be acknowledged. First, this was a single-center retrospective study without randomization. Patients with moderate-to-severe hydronephrosis, larger stone burden, or smaller IPA tended to undergo mPCNL, introducing potential selection bias. In addition, treatment allocation was based on clinical decision-making rather than random assignment, and residual confounding from unmeasured factors cannot be fully excluded. Second, no formal prospective sample size calculation or power analysis was performed because of the retrospective design, and the sample size was determined by the number of eligible consecutive patients treated during the study period. Third, stone-free status was assessed using KUB radiography, which has limited sensitivity for detecting small residual fragments and may, therefore, have led to underestimation of residual stone burden. Finally, stone-free status was defined as residual fragments <4 mm, a threshold that has been adopted in previous endourological studies as a clinically acceptable cutoff for insignificant residual fragments, although the optimal definition remains debated. These limitations may have influenced the observed outcomes. Therefore, multicenter prospective studies with larger sample sizes, standardized treatment selection, and more sensitive imaging-based follow-up are warranted to validate our findings.

Conclusion

Overall, FV-UAS–assisted fURL appears to be a safe and effective option for the management of 2–3 cm renal stones. Compared with conventional UAS–assisted fURL, FV-UAS–assisted fURL was associated with a shorter operative time, shorter postoperative length of stay, and lower total hospitalization costs. Compared with mPCNL, FV-UAS–assisted fURL showed advantages in bleeding-related outcomes, postoperative recovery, and patient comfort, while achieving a short-term SFR comparable to that of mPCNL. Therefore, FV-UAS–assisted fURL may serve as a minimally invasive alternative for 2–3 cm renal stones, offering a practical balance between stone clearance efficiency and procedural burden in patients with a medium stone load.