Temporal Trends and Treatment Outcomes of Flexible Ureteroscopy for Lower Pole Stones in a Tertiary Referral Stone Center

Abstract

Introduction:

To evaluate trends in efficacy and safety of flexible ureteroscopy (fURS) for the treatment of lower pole stones (LPS) over a 6-year period and to compare the annual outcomes after one fURS procedure retrospectively.

Patients and Methods:

Four hundred nine patients were treated for pure LPS. An analysis of the annual outcomes regarding patient characteristics, operative parameters, stone-free rates (SFRs), and complication rates (CRs) was performed. The SFR was stratified according to stone size and number of stones per patient. Patient data are expressed as mean±standard deviation.

Results:

There were no annual differences regarding age, body–mass index, stone size (7.09±4.31 mm), number of stones per patient (1.66±2.86), operative time (52.93±33.58 minutes), use of postoperative stents (59.2%), and the Ho:YAG laser lithotripsy rate (49.4%) during the 6-year period. Total primary SFR (annual range) of 97.6% (88.2%–100%), 89.1% (82.9%–96.3%), 71% (60%–78.6%) for urinary calculi <5 mm (3.43±0.78 mm), 5–9 mm (6.69±1.34 mm), and ≥10 mm (13.09±6.02 mm) could be demonstrated over the 6-year period. The total SFR differed significantly between urinary calculi <5 mm, 5–9 mm, and those ≥10 mm (p<0.0179). The SFR (annual range) decreased from 90% (86.2%–95.4%) in patients with 1 stone to 84.1% (60%–100%) in those with ≥3 stones. Perioperative complications (annual range) occurred in 9.7% (6%–13.6%) of the patients (Clavien I 5.1% [1.2%–8.6%], Clavien II 2% [0%–4.9%], Clavien IIIa 0.9% [0%–3.4%], Clavien IIIb 1.7% [1.2%–4.8%]) without differences in the annual CR.

Conclusions:

fURS is a safe and efficacious procedure for the treatment of LPS with high primary SFR and low CR. fURS in larger LPS (≥10 mm) is associated with the risk for staged procedures.

Introduction

Flexible ureteroscopy (fURS) has gained rising popularity for the treatment of upper tract calculi. Based on the stone size, stone location, and the definition of stone-free status, stone-free rates (SFRs) up to 100% have been reported after fURS.^1
–3 The current guidelines of the European Association of Urology for urolithiasis recommend fURS and shock wave lithotripsy (SWL) as the first-line treatment for lower pole stones (LPS) ≤2 cm in diameter.³ Unfavorable outcomes for the treatment of LPS through fURS have been identified: the collecting system's anatomy,^4
–6 stone size (>10 mm),^4,7

–11 multiple stones, or multiple locations.^7,12 However, the outcomes of these series are limited by treating LPS combined with stones in different intrarenal locations,^7,13 sample size (<100 patients),^{4,9

–12,14

–17} or treatment of large stone burden in case series (<40 patients).^{8
–10,11,18,19} Up to date, no study has analyzed the development of SFRs and complication rates (CRs) for the treatment of pure LPS with fURS over a certain period of time. The aim of our study was to examine the immediate SFR and CR after fURS for pure LPS in a large retrospective study and, as a novelty, to compare the annual outcomes of fURS over a 6-year period, respectively.

Patients and Methods

A retrospective review of our prospectively recorded database was performed. Four hundred nine out of 2364 patients who received ureteroscopic stone treatment at our institution were identified as being treated for pure LPS.

An analysis of the annual outcomes regarding patient characteristics (age, gender, body–mass index [BMI], stone size [mm], number of stones/patient, operative time [OT, minutes], use of preoperative/postoperative ureteral stents, Holmium:YAG laser lithotripsy), the primary SFR, and the CR was performed. The indications for ureteral prestenting and postoperative ureteral stent placement have been previously reported in detail.²⁰ The ureteroscopy (URS) procedures were done by a total of 17 surgeons (5 consultants and 12 residents). Resident fURS was carried out according to our mentor-based URS training program: the consultant served as a mentor for the residents in the operating room.²¹ The SFR was stratified according to the stone size (<5, 5–9, and ≥10 mm) and the number of stones per patient, and given for each year. The stone size was assessed preoperatively on kidney, ureter, and bladder radiograph (KUB), a noncontrast CT of the abdomen with a renal stone protocol, and/or intravenous urogram (IVU) using the largest stone diameter of the solitary calculus or the largest diameter of the largest stone in patients with multiple calculi.^20,21 Patients with incidental findings of additional stones in other locations than the lower pole of the kidney during fURS were excluded from our retrospective analysis.

The URS procedure and the equipment used were previously described in detail.^20,21 Briefly, fURS was performed with a 6F (Viper/Cobra; R. Wolf, Knittlingen, Germany) or 7.5F flexible ureterorenoscope (Flex-X2; Karl Storz, Tuttlingen, Germany). The SFR was determined the day after the fURS procedure with renal ultrasound (US) and KUB to ensure the absence of residual stones and/or hydronephrosis. An IVU or CT was performed if there was any concern regarding residual stones or in cases of radiolucent stones.^20,21 The complications were assessed according to the modified Clavien classification system (CCS) by a resident who was not involved in the surgical procedures.^22,23

Statistical analysis was performed using SPSS for Windows. Patient data are expressed as mean±standard deviation (range). Differences in nonparametric parameters were calculated using the Kruskal–Wallis test, while categorical variables were compared using the chi-square test. A p-value <0.05 was considered statistically significant.

Results

Table 1 lists the baseline characteristics and the perioperative data of the patients. There were no significant annual differences during the 6-year period regarding age (51.65±15.45 years), BMI (27.86±5.72 kg/m²), stone size (7.09±4.31 mm), number of stones per patient (1.66±2.86), OT (52.93±33.58 minutes), use of preoperative (95.6%) or postoperative ureteral stents (59.2%), and the rate of Holmium:YAG laser lithotripsy (49.4%), respectively. The majority of the fURS procedures (n=318, 77%) were performed by the consultants of the department without a trend during the 6-year period.

Table 1.

Patient and Stone Characteristics

	Total	Year 1	Year 2	Year 3	Year 4	Year 5	Year 6	p-Value
No. of patients	409	42	76	69	58	81	83
Age (years)	51.65±15.45 (13–85)	50.9±17.05 (17–82)	49.41±15.39 (21–85)	51.64±13.24 (21–84)	49.03±16.8 (13–82)	53.91±15.52 (19–84)	53.7±15.17 (24–83)	n.s.
BMI (kg/m²)	27.86±5.72 (17.54–60.2)	NA	28.25±5.45 (20.10–43)	28.09±6.09 (19.8–60.2)	27.82±6.33 (17.96–50.37)	27.06±5.01 (18.94–46.09)	28.48±5.88 (17.54–44.24)	n.s.
Stone size (mm)	7.09±4.31 (1–42)	6.41±3.23 (3–16)	7.55±3.95 (2–18)	6.29±3 (2–15)	7.47±3.89 (3–25)	6.38±2.39 (2–13)	7.9±6.66 (1–42)	n.s.
No. of stones/patient	1.66±2.86 (1–50)	1.38±0.71 (1–3)	1.66±1.33 (1–9)	1.64±2.5 (1–20)	1.62±1.25 (1–8)	2.07±5.6 (1–50)	1.45±1.15 (1–7)	n.s.
Gender, n (%)								n.s.
M	268 (65.5)	26 (61.9)	47 (61.8)	41 (59.4)	43 (74.1)	58 (71.6)	53 (63.9)	n.s.
F	141 (34.5)	16 (38.1)	29 (38.2)	28 (40.6)	15 (25.9)	23 (28.4)	30 (36.1)	n.s.
No. of stones (%)
1	306 (74.8)	32 (76.2)	51 (67.1)	55 (79.7)	38 (65.5)	65 (80.2)	65 (78.3)
2	59 (14.4)	5 (11.9)	14 (18.4)	8 (11.6)	13 (22.4)	8 (9.9)	11 (13.3)
3	23 (5.6)	5 (11.9)	5 (6.6)	4 (5.8)	4 (6.9)	3 (3.7)	2 (2.4)
4 or greater	21 (5.2)	—	6 (7.9)	2 (2.9)	3 (5.2)	5 (6.2)	5 (6.02)
No. of preoperative stent (%)	395 (95.6)	40 (95.2)	76 (100)	66 (95.7)	57 (98.3)	75 (92.6)	81 (97.6)	n.s.
No. of postoperative stent (%)	242 (59.2)	26 (61.9)	39 (51.3)	41 (59.4)	32 (55.2)	49 (60.5)	55 (66.3)	n.s.
No. of laser lithotripsies (%)	202 (49.4)	18 (42.9)	41 (53.9)	35 (50.7)	26 (44.8)	38 (46.9)	44 (53)	n.s.
No. of scope types (%)
Flexible	126 (30.8)	26 (61.9)	48 (63.2)	29 (42)	12 (20.7)	3 (3.7)	8 (9.6)
Flexible+semirigid	283 (69.2)	16 (38.1)	28 (36.8)	40 (58)	46 (79.3)	78 (96.3)	75 (90.4)
Surgeons
Consultants (%)	318 (77.7)	27 (64.3)	47 (61.8)	63 (91.3)	44 (75.9)	64 (79)	73 (88)
Residents (%)	91 (22.3)	15 (35.7)	29 (38.2)	6 (8.7)	14 (24.1)	17 (21)	10 (12)
Operative time (minutes)	52.93±33.58 (3–194)	62.84±41.44 (11–170)	52.09±29.21 (13–160)	59.85±36.33 (15–145)	51.92±34.42 (15–194)	46.14±33.51 (10–176)	49.85±28.71 (3–135)	n.s.

Data indicated as mean value±standard deviation (range).

BMI=body–mass index; NA=not analyzed; n.s.=not significant.

Table 2 summarizes the primary SFR after one fURS over the 6-year period. The total primary SFR (annual range) over the 6-year period was 88% (83.2%–94%). The total SFR (annual range) of 97.6% (88.2%–100%), 89.1% (82.9%–96.3%), 71% (60%–78.6%) for urinary calculi <5, 5–9, and ≥10 mm could be demonstrated over the 6-year period, corresponding to mean stone sizes of 3.43±0.78, 6.69±1.34, and 13.09±6.02 mm, respectively. The total SFR differed significantly between urinary calculi <5, 5–9 mm, and those ≥10 mm (p<0.0179). The SFR (annual range) decreased from 90% (86.2%–95.4%) in patients with 1 LPS to 84.1% (60%–100%) in those with ≥3 LPS.

Table 2.

Clinical Characteristics and Surgery Outcome

	Total	Year 1	Year 2	Year 3	Year 4	Year 5	Year 6	p-Value
No. of patients	409	42	76	69	58	81	83
No. of patients stone free (%)
One procedure	88	83.2	85.5	85.5	82.8	92.6	94
Lower kidney pole
Stone size ≥10 mm
No. of patients stone free (%)	71^a,c	60	76.5	71.4	63.6	62.5	78.6
Stone size (mm)	13.09±6.02 (10–42)	12.34±2.16 (10–16)	12.72±3.11 (10–18)	11.93±2.01 (10–15)	12.64±4.5 (10–25)	10.5±1.07 (10–13)	16.21±11.08 (10–42)	0.305
Stone size 5–9 mm
No. of patients stone free (%)	89.1	85	82.9	84.3	84.2	95.1	96.3
Stone size (mm)	6.69±1.34 (5–10)	7.47±1.66 (5–10)	7.14±1.32 (5–9)	6.09±1.2 (5–9)	6.67±1.25 (5–8)	6.42±1.38 (5–9)	6.73±1.3 (5–9)	≤0.009
Stone size <5 mm
No. of patients stone free (%)	97.6^b	88.2	100	100	100	100	100	0.605
Stone size (mm)	3.43±0.78 (1–5)	3.67±0.58 (3–4)	3.35±1.0 (2–5)	3.23±0.82 (2–4)	3.56±0.53 (3–4)	3.52±0.66 (2–4)	3.27±0.88 (1–4)
No. of patients stone free (%)
One procedure	88	83.2	85.5	85.5	82.8	92.6	94
One stone	90	86.2	86.3	88.5	89.5	90.8	95.4
Stone size (mm)	6.67±4.3 (1–42)	6.23±3.57 (3–16)	6.02±2.67 (2–14)	5.53±2.1 (2–12)	6.76±2.65 (3–14)	6.6±2.33 (3–13)	8.07±7.28 (1–42)	0.147
Two stones	81.4	100	78.6	62.5	69.2	100	90.9
Stone size (mm)	7.69±3.36 (2–18)	5.88±2.3 (3–8)	8.53±4.32 (2–18)	8.21±3.21 (4–14)	7.85±3.85 (3–15)	6±1.83 (4–8)	7.5±2.7 (4–10)	0.665
≥3 Stones	84.1	60	90.9	83.3	71.4	100	85.7
Stone size (mm)	9.15±4.93 (2–25)	7.34±2.5 (4–10)	12.27±3.85 (7–18)	12.33±3.06 (9–15)	10.5±7.45 (5–25)	5.38±2.93 (2–10)	6.6±3.78 (3–12)	≤0.007

p<0.0002 (stone size ≥10 mm vs 5–9 mm).

p<0.0001 (stone size ≥10 mm vs<5 mm).

p<0.0179 (stone size ≥10 mm vs 5–9 mm vs<5 mm).

Table 3 lists detailed information on all complications. The total perioperative CR (annual range) was 9.7% (6%–13.6%). Minor complications occurred in 7.1% (Clavien I: 5.1%; Clavien II: 2%) and major complications in 2.7% (Clavien IIIa: 0.7%, Clavien IIIb: 1.7%) of the patients, respectively. There were no clear trends in the annual occurrence (total, range) of Clavien I (5.1%, 1.2%–8.6%), Clavien II (2%, 0%–4.9%), Clavien IIIa (0.9%, 0%–3.4%), and Clavien IIIb (1.7%, 1.2%–4.8%) complications.

Table 3.

Detailed Analysis of Complications According to the Clavien Classification System Stratified by Year of Surgery

Complication	Treatment	Total	Year 1	Year 2	Year 3	Year 4	Year 5	Year 6
No. of patients		409	42	76	69	58	81	83
Clavien grade I complications (n=21 of 409; 5.1%)
Prolonged pain	Oral analgetics	10 (2.4)	1 (2.4)	4 (5.3)	3 (4.3)	0 (0)	1 (1.2)	1 (1.2)
Hematuria	Bedside catheterization and/or bladder irrigation and/or prolonged catheterization	3 (0.7)	1 (2.4)	0 (0)	1 (1.4)	1 (1.7)	0 (0)	0 (0)
Paravasation (mucosal injury without visible mucosal perforation [contrast media outflow])	Prolonged Double-J stenting without further therapy	8 (2)	0 (0)	2 (2.6)	2 (2.9)	1 (1.7)	3 (3.7)	0 (0)
Clavien grade II complications (n=8 of 409; 2%)
Urinary-tract infections with signs of bacteremia (fever >38.5°C)	Parenteral antibiotics	8 (2)	0 (0)	1 (1.3)	1 (1.4)	1 (1.7)	4 (4.9)	1 (1.2)
Clavien grade IIIa complications (n=4 of 409; 0.9%)
Hydronephrosis with flank pain	Ureteral stent (Double-J stent)	4 (0.9)	0 (0)	0 (0)	0 (0)	2 (3.4)	2 (2.5)	0 (0)
Clavien grade IIIb complications (n=7 of 409; 1.7%)
Ureteral perforation	Prolonged Double-J stenting, control ureteroscopy after stent removal	7 (1.7)	2 (4.8)	1 (1.3)	1 (1.4)	1 (1.7)	1 (1.2)	1 (1.2)
Clavien grade IV complications (n=0 of 409; 0%)
Life-threatening complications	ICU management	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)
Clavien grade V complications (n=0 of 409; 0%)
Death	—	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)
Total No. of complications		40 (9.7)	4 (9.5)	8 (10.5)	8 (11.6)	6 (10.3)	11 (13.6)	3 (3.6)

ICU=intensive care unit.

Discussion

The key results of our large retrospective analysis of fURS for pure LPS were high primary SFR and low perioperative CR after one fURS procedure. To the best of our knowledge, there has been no other study with such a high number of pure LPS treated by fURS reported.^{4

–15,17} The total primary SFR in this series depended on stone size and the number of LPS. We were able to demonstrate an association of the size of LPS (≥10 mm) and the risk of staged fURS procedures. This is reflected by the annual SFR not exceeding 78.6% without a trend toward lower or higher SFR over the 6-year period.

The total SFR (88%) in this series for LPS (mean stone size 7.09±4.31 mm) is well comparable to series of similar stone size. Jessen and colleagues found an SFR of 88.3% in 111 patients with a total mean stone size of 7.47±3.95 mm, while Perlmutter and colleagues had an SFR of 90.9% in 44 patients with LPS of median 6.89 mm.^5,15 A stratification of the SFR according to stone size was not performed in these series.^5,15 In a prospective randomized trial (PRT) comparing fURS, observation, and SWL for the treatment of LPS, Sener and colleagues found an SFR of 92% after fURS in patients with a mean stone size of 8.2±1.2 mm.²⁴ In contrast, Pearle and colleagues found an SFR of 72% in patients with mean stone dimensions of 6.9×5 mm after fURS for LPS in a multicentric PRT comparing fURS with SWL.¹⁴ Although these outcomes are robust due to the multicentric randomized approach, the data of this PRT were collected from 2000 to 2003. Therefore, a higher SFR, due to technical improvements of URS instrumentation and its auxiliary devices nowadays, is expected.¹⁴ Currently, Jacquemet and colleagues indicated a total SFR of only 68.3% and an SFR of 79.2% in patients with LPS <10 mm at 6-month follow-up.⁷ This lower total SFR compared to our series is based on three findings: First, the total mean stone size was 9.6±5.67 mm, which is higher than in our series.⁷ Second, the LPS group (n=232) consisted of LPS combined with renal stones in different locations. Third, the final SFR was defined on radiographic findings (KUB with US or CT) 6 months after fURS.⁷ It remains therefore unclear whether new stones or residual stones were found at 6-month follow-up.⁷

The total SFR (71%) in our series for LPS ≥10 mm (mean stone size 13.09±6.02 mm) is well comparable to the literature. Knoll and colleagues found an SFR of 71.5% in 21 patients (mean stone size of 19±4 mm) 1 day after fURS for single LPS.⁸ Ozturk and colleagues had an SFR of 73% in 38 patients (mean stone size 17.3±1.45 mm).¹⁰ Martin and colleagues found an SFR of only 66.6% in 89 patients after fURS of LPS (mean stone size 12.02±5.7 mm) of whom 32.6% had multiple LPS.¹² In a retrospective multivariate analysis, Jacquemet and colleagues did not find any impact of LPS on the efficacy and morbidity of fURS. However, multiple locations and stone size ≥10 mm significantly decreased the SFR,⁷ which could be confirmed by our series. We found a significant decrease of the total SFR from 90% in patients with 1 LPS compared to 84.1% in those with ≥3 stones. In addition, the total SFR differed significantly between urinary calculi <5 mm (97.6%), 5–9 mm (89.1%), and those ≥10 mm (71%). In some series (n=36–88 patients)^4,9,11,16 with large stone diameter (range, 10.2±2.9–16.88±3.48 mm)^4,11,16 or high stone burden (1.65±0.69 cm²),⁹ a high SFR at day 1 (range, 78.4%–91.6%)^4,9,11,16 was achieved. However, three of these small retrospective series were from the same center of excellence, which restricts the evidence for high immediate SFR (>80%) after one fURS for LPS >10 mm.

The total CR for the treatment of pure LPS with fURS in this study was low (9.7%) and well comparable with the current literature. Jacquemet and colleagues found a total CR of 9.1% in patients with a mean stone size of 9.6±5.67 mm (Clavien I: 2.2%, Clavien II: 6.9%), although the group consisted of LPS combined with renal stones in different renal locations.⁷ While Jessen and colleagues indicated a total CR of 19.8% (Clavien I: 3.6%, Clavien II: 11%, Clavien IIIa: 4.5%, Clavien IIIb: 0.9%, Clavien IV: 0.9%) for the treatment of LPS,⁵ Ozturk and colleagues found a total CR of 5.26% (Clavien I: 2.6%, Clavien IIIb 2.6%).¹⁰ In other series describing the treatment of LPS through fURS, the CRs according to the CCS, ranging from 7.7% to 9.8%,^12,16 were not indicated^4,6,14,15 or classified as major (1.9%)¹³ or minor complications (range, 7.8%–23.8%).^8,9,11,13 These CRs for fURS are contrary to Mandal and colleagues who applied the modified CCS on semirigid URS for ureteral stones.²³ They reported a CR of 30% in primary unstented patients, but a substantial number of patients had minor complications like transient hematuria or urinary-tract infections.²³ All procedures were performed in unstented patients.²³ In contrast, one reason for the low CR and high SFR in our series might be the high (95.6%) prestenting rate. Ureteral prestenting has been shown to lower the incidence of ureteral injury, decrease the OT, and to facilitate stone extraction resulting in a higher SFR.^{20,21,25
–27}

Finally, our outcomes regarding the SFR and CR can be considered to be robust. The baseline parameters (age, BMI, stone size, number of stones/patient, OT, use of pre- and postoperative ureteral stents, Holmium:YAG laser lithotripsy rate) did not change over the 6-year period. In addition, we did not find any trend to treat larger or smaller LPS during this period. These baseline data (age, BMI, number of stones/patients) are in line with other fURS series for LPS.^7,12,14 Differences in the OT and the postoperative ureteral stenting rate between our series and the literature could be explained due to the high (95.6%) prestenting rate compared to other studies (43.8%–72%)^5,7,8,12,15: The mean OT in our series was 52.9 minutes, which was shorter than in studies of comparable LPS size (61–90 minutes).^9,13,14 In addition, the postoperative ureteral stenting rate was 59.2%, which was lower than in comparable fURS series (70.8%–100%).^5,8,9,11,12

Two factors that might have affected the SFR and the CR over the 6-year observation period have not been assessed in our series: first, the collecting system's anatomy, that is, a long infundibulum⁶ and an acute infundibulopelvic angle (<30°),^4,5 has been shown to negatively affect the SFR. Second, the quality of the flexible ureterorenoscopes and the decrease of the quality of the scopes over time (loss of deflection, irrigation flow, and broken image fibers) and its impact on OT, SFR, and CR have not been assessed.²⁸ However, a high SFR and low CR were achieved with conventional fiberoptic ureterorenoscopes with adequate OT in this series, although advantages of digital next-generation chip on the tip scopes with regard to the OT have been shown.²⁹ Another factor that might impact the SFR and CR could be the learning curve of the surgeon. However, the proportion of high consultant to low resident fURS procedures for LPS remained constant over the 6-year period, which argues against a significant impact of the learning curve on the SFR and CR in this series. In addition, a negative impact on the fURS outcomes due to resident training is considered to be low. This can be seen as a result of our mentor-based URS training program with the consultant serving as a mentor in the operating room guaranteeing a high-quality procedure.²¹

The primary SFR was routinely determined by an endoscopic examination, postoperative KUB, and US in our study, but the adequate imaging method is still a controversial issue. In other studies, which analyzed fURS for LPS, the SFR was determined by KUB/US (71.5%–91.6%),^4,5,8

–11 US (92.2%),¹³ or KUB (94.2%),¹⁵ which may overestimate the SFR compared to CT (50%–74.1%).^7,12,14 However, these differences in the SFR might be due to different stone sizes and date of imaging: mean 6.6 to 19 mm in those with postoperative KUB/US,^4,5,8

–11 mean 6.6 mm in those with US,¹³ and mean 6.9 to 12.02 mm in those with CT,^7,12,14 respectively. The SFR was assessed on postoperative day 1,^5,8,11 at 2 weeks,¹⁵ at 1 to 2 months,^4,12,13 at 3 months,¹⁴ at 6 months,⁷ or not clearly stated.^6,9,10 However, the proposed definition of clinically insignificant residual urinary calculi (<3 mm) together with a mean stone size of 7.09 mm minimizes the probability to overestimate the SFR in our study.^3,20,30

We present the largest series for the treatment of LPS with fURS so far with high primary SFR and low CR over a 6-year period. However, there is a lack of evidence for the treatment of LPS with only few high quality PRTs, which we cannot enhance with our retrospective data.³¹ In contrast, our study contributes relevant information to the fURS literature. We did not find any trends in the baseline parameters of the patients with constant outcomes regarding the SFR and CR over the 6-year period. Three reasons for a nearly constant SFR over the 6-year period have to be discussed: First, achieving the limits of our institutional learning curve, that is, further improvements of the SFR would be slight and difficult to achieve. Second, the impact of the individual collecting system's anatomy on SFR of fURS for LPS stones, which was not assessed in this retrospective series.^4,5 Third, the impact of novel technologies (e.g., ureteral access sheaths, laser fibers, dormia baskets, or safety wires) for fURS on SFR, which is again difficult to determine from our retrospective data. On the other hand, all fURS procedures were carried out with fiberoptic ureterorenoscopes and Ho:YAG laser lithotripters when necessary.

The low SFR (71.4%) in patients with LPS ≥10 mm over the 6-year period is another major result of our study, which comprises the risk for staged fURS procedures in this subgroup of LPS. The 10 mm diameter appears to be a kind of an invisible threshold for LPS associated with a significantly lower SFR during fURS if exceeded. These important result might be helpful information for patient counseling to choose the adequate treatment for larger (≥10 mm) LPS.

Conclusions

fURS is a safe and efficacious procedure for the treatment of LPS with high primary SFR and low perioperative CR. However, fURS in larger LPS (≥10 mm) was associated with a lower SFR and the risk for staged fURS procedures. These results are helpful for patient counseling to choose the adequate treatment for larger (≥10 mm) LPS.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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