Does Relocation of Lower Pole Stone During Retrograde Intrarenal Surgery Improve Stone-Free Rate? A Prospective Randomized Study

Abstract

Purpose:

The aim of this study was to compare the stone-free rate (SFR) of in situ treatment vs relocation and lithotripsy for lower pole stones of less than 2 cm following retrograde intrarenal surgery (RIRS).

Methods:

This prospective randomized study was undertaken from June 2019 to May 2020 in patients undergoing RIRS for lower pole renal stones less than 2 cm in diameter. Patients were randomized into two groups: in situ lithotripsy group and relocation lithotripsy group. The in situ lithotripsy group underwent laser lithotripsy for lower pole stones without relocation of the calculus, and the relocation lithotripsy group had their stones relocated to a favorable location using a tipless Nitinol basket, followed by laser lithotripsy. Laser lithotripsy was achieved using the holmium:YAG (Ho:YAG) laser (120 W) with a 200-μm laser fiber. A Double-J stent was placed in all patients at the end of the procedure. Patient demographics, stone characteristics, operative outcomes, and complications were evaluated. The SFR was determined at 1 month postoperatively with a kidney, ureter, and bladder radiograph (KUB) and ultrasound KUB.

Results:

Sixty-eight patients were included in the study: in situ group (n = 35) and relocation group (n = 33). The mean stone size and stone density were similar between the groups. The total operative duration, lasing duration, and total energy used were similar between the groups. At the 1-month follow-up, the complete SFR was 85.7% and 91% in the in situ lithotripsy and relocation lithotripsy groups, respectively (p = 0.506).

Conclusions:

Relocation followed by subsequent laser lithotripsy was associated with similar SFRs as with in situ laser lithotripsy for lower pole renal calculi less than 2 cm in diameter following RIRS using the Ho:YAG laser.

Introduction

Lower pole renal stones are more likely to require treatment due to reduced chances of spontaneous passage.^1,2 Retrograde intrarenal surgery (RIRS) is a recommended treatment for lower pole stones less than 2 cm.^3,4 However, the stone-free rate (SFR) following RIRS has been lower for these stones than in other locations.^5,6 Unfavorable anatomic factors of the lower pole such as narrow infundibular width, long infundibulum, and acute infundibulopelvic angle limit effective lithotripsy, and the dependent location hinders spontaneous passage of fragments.^7
–9

Various methods such as active extraction of fragments and relocation of calculus have been suggested to improve the SFR by reducing the retention of fragments in the lower pole.^10

–13 Active extraction is associated with a longer operative duration and increased risk of ureteral injury, and even after active retrieval, small fragments still remain in the kidney.^14,15 Relocation of the calculus to a more favorable location may improve the efficiency of laser lithotripsy and facilitate spontaneous passage of fragments by circumventing the unfavorable anatomy.^10,12,13,16

The available studies assessing the efficacy of relocation were conducted before the advent of the high-power laser machine. Hence, this study was undertaken to assess the role of relocation before lithotripsy for lower pole calculi in the present context.

Methodology

This prospective randomized study was conducted from June 2019 to May 2020. Ethical clearance was obtained from the Institutional Review Board of National Academy of Medical Sciences, Bir Hospital, Kathmandu, Nepal, and written informed consent was obtained from all patients.

Patients undergoing RIRS for lower pole renal stones ≤2 cm were included. Patients with coexistent calculi in other calices or the ureter; with anomalies such as concomitant ureteropelvic junction obstruction, ureteral stricture, caliceal diverticulum, anomalous kidney, polycystic kidney disease, and medullary sponge kidney; and those with active urinary infection were excluded.

Randomization was done using sequentially numbered, opaque sealed envelopes.¹⁷ Patients were divided into two groups: in situ lithotripsy group and relocation lithotripsy group. The in situ lithotripsy group underwent lithotripsy in the lower pole without relocation, and the relocation lithotripsy group had their stones relocated to a favorable location, followed by lithotripsy.

The primary objective was to compare SFRs between the two groups at 4 weeks. The secondary objective was to compare the preoperative, intraoperative, and postoperative characteristics between the groups.

Preoperative urine analysis, coagulation test, complete blood count, serum biochemistry, and CT KUB reports were obtained. Preoperative sterile urine culture was performed. A single experienced surgeon (A.S.) performed all the surgeries.

Prophylactic antibiotic (ceftriaxone 1 gm) was administered during induction of general anesthesia. With the patient in the dorsal lithotomy position, rigid cystoscopy was performed to place a 0.035″ hydrophilic guidewire (Terumo, Japan) into the renal collecting system under fluoroscopic guidance.

The ureteral access sheath (UAS) (9.5/11.5 or 10/12F) was routinely used and a sheathless procedure was done in cases where the UAS was not negotiable. In those cases, with the ureter not permitting even a sheathless procedure, a Double-J stent was placed and the procedure was performed after 2 weeks. Flex X^c, Flex X2 (7.5F; Karl Storz, Tuttlingen, Germany), and URF-P6 (7.95F; Olympus, Japan) flexible ureterorenoscopes were used. Irrigation was done under gravity with occasional manual pumping by an assistant using TraxerFlow (Rocamed, Monaco).

After an initial retrograde pyelogram and thorough inspection of the pelvis and calices, the lower pole stone was relocated using a tipless Nitinol basket (N-circle, 2.2F 115 cm; Cook Medical, USA) to a favorable calix based on lithotripsy ergonomics and drainage as judged by the surgeon intraoperatively in the relocation group. Large calculi that could not be engaged in the basket were fragmented and the fragments were relocated to the desired calix for further lithotripsy (Fig. 1).

FIG. 1.

Intraoperative photographs depicting relocation of a lower pole calculus. A ureteroscope in the lower pole calix with a calculus engaged in a tipless Nitinol basket (A, B). Engaged calculus being relocated to the upper pole calix (C). Color images are available online.

Laser lithotripsy was done using the holmium:YAG laser (Pulse 120 H; Lumenis Inc., Israel) with a 200-μm fiber and the following laser settings were used: dusting in situ: 0.6–0.8 J, 12–15 Hz; fragmentation of stones before relocation: 0.8–1 J, 8–10 Hz; and pop-dusting: 0.5 J, 50 Hz. Lithotripsy was done till the dust floated or the fragments could be easily washed out with gentle irrigation pressure.

On completion of lithotripsy, few fragments were removed using the basket for stone analysis, while complete removal of fragments with the basket was not done in any patient. A Double-J stent was placed at the end of the procedure.

Patients were routinely discharged on the 1st postoperative day. The Double-J stent was removed at 2 weeks postoperatively and the SFR was assessed at 4 weeks using the kidney, ureter, and bladder radiograph (KUB) and ultrasonogram (USG)-KUB. The stone was measured in its largest dimension from the preoperative CT KUB and the largest diameters were summed up in case of multiple stones.

The duration of surgery was calculated from the time of initial cystoscope insertion to placement of the Double-J stent. Lasing duration and total energy used were recorded. Complete stone-free status was defined as the absence of stone fragments in both KUB and USG-KUB reports at 4 weeks. Perioperative complications were classified using the modified Clavien-Dindo system.¹⁸

The patients were followed up for 3 months and those with symptoms at any time and fragments ≥5 mm at 3 months underwent repeat surgery. Preoperative, intraoperative, and postoperative characteristics were compared between the groups.

We estimated a sample of 35 patients in each group with 95% confidence interval, 0.70 effect size, and 80% power. The noncompliance rate of 10% was also factored into the sample size calculation. Categorical variables and continuous variables are presented as number (%) and median/mean (±standard deviation [SD]), respectively. Chi-square/Fisher's exact test and Student t-test/Mann–Whitney U test were used to analyze categorical and continuous variables, respectively.

Statistical analysis was done using the Statistical Package for the Social Sciences, version 23.0 (SPSS Inc., Chicago, IL). All comparisons were two-tailed and p < 0.05 was considered statistically significant.

Results

A total of 68 patients were included in the final analysis (Fig. 2). Demographic characteristics of the patients are presented in Table 1. There was male predominance in both the groups. The overall mean age (SD) of participants was 37.3 (13.38) years and participants in the relocation group were older compared with the in situ group (p = 0.004). There was no difference with regard to the laterality of the stone (Table 1). Majority of the stones were relocated to the upper pole (n = 21, 63%), followed by the interpolar calix (n = 12, 37%).

FIG. 2.

Patient enrollment algorithm. LPC = lower pole calix; MPC = interpolar calix; UPC = upper pole calix.

Table 1.

Comparison of Patient Demographics and Stone Characteristics Between the Groups

Parameters	In situ group (n = 35), n (%)	Relocation group (n = 33), n (%)	p
Sex
Male	22 (62.9)	26 (78.8)	0.150^a
Female	13 (37.1)	7 (21.2)
Age (years)	32.88 ± 12.03	42.00 ± 13.30	0.004^b
BMI (kg/m²)	23.82 ± 3.43	24.08 ± 3.89	0.734^a
Laterality
Left	19 (54.3)	18 (54.5)	0.983^a
Right	16 (45.7)	15 (45.5)
Stone size, overall mm	11.74 ± 3.12	11.98 ± 3.18	0.747^b
<10 mm	10 (28.6)	9 (27.3)
10–15 mm	22 (62.9)	18 (54.5)
15–20 mm	3 (8.6)	6 (18.2)
Stone density (HU)	966.42 ± 326.23	1102.97 ± 279.04	0.069^b
Preoperative stenting
No	25 (71.4)	29 (87.9)	0.094^a
Yes	10 (28.6)	4 (12.1)

Data are presented as mean ± SD and n (%).

Chi-square test.

t-Test.

BMI = body mass index; HU = Hounsfield unit; SD = standard deviation.

The overall mean stone size (SD) was 11.86 (3.13) mm and comparable between the groups (p = 0.620). Majority of patients (81.6%) had a stone larger than 10 mm. The mean stone density was similar between the groups. Fourteen patients (20.5%) underwent preoperative stent placement (Table 1).

Although the mean operative duration was slightly longer in the relocation group, it was not statistically significant (p = 0.077). Median lasing duration and total laser energy used were similar in both groups (Table 2). The majority of patients underwent RIRS with placement of UAS, and 10/12F and 9.5/11.5F UASs were most frequently used in the in situ and relocation groups, respectively (Table 2).

Table 2.

Comparison of Operative and Postoperative Characteristics Between the Groups

Parameters	In situ group (n = 35), n (%)	Relocation group (n = 33), n (%)	p
Operative duration (minutes)	42.57 ± 13.67	48.30 ± 12.55	0.077^a
<10 mm	37.40 ± 10.73	46.55 ± 11.53	0.091
10–15 mm	42.77 ± 13.53	46.38 ± 8.28	0.328
15–20 mm	58.33 ± 15.27	56.66 ± 21.45	0.909
UAS use			0.021^b
Sheathless	9 (25.7)	6 (18.2)
9.5/11.5F	6 (17.1)	16 (48.5)
10/12F	20 (57.2)	11 (33.3)
Lasing duration (seconds) median (Q1, Q3)	663.0 (402, 1045)	885 (615, 1140)	0.332^c
<10 mm	425 (203, 702)	773 (458, 987)	0.179^c
10–15 mm	826 (501, 1198)	899 (752, 1140)	0.751
15–20 mm	1070 (636, 1184)	1113 (312, 2340)	1.00
Energy used (KJ) median (Q1, Q3)	7.42 (3.83, 13.15)	8.60 (5.24, 10.00)	1.000^c
<10 mm	4.88 (3.410, 7.20)	4.76 (3.31, 6.80)	0.673^c
10–15 mm	9.23 (3.83, 15.0)	9.3 (5.03, 10.8)	0.897
15–20 mm	12.20 (4.47, 13.44)	12.60 (4.82, 14.12)	1.000
Overall SFR	30 (85.7)	30 (91)	0.506^b
Clearance with stone size
<10 mm	9 (90)	9 (100)	1.000
10–15 mm	20 (90.9)	17 (94.4)	1.000
15–20 mm	1 (33.3)	4 (66.6)	0.524
Residual fragment, (mm) range	3–6	3–6
Residual fragment location
Upper pole	0	0
Interpolar region	0	1
Lower pole	5	2
Need of auxiliary procedures
RIRS	1	0
Complications	5	6	0.749
Clavien grade >I	1	2

Data are presented as mean ± SD and n (%).

t-Test.

Chi-square test.

Mann–Whitney U test.

KJ = kilojoule; Q1 = first quartile; Q3 = third quartile; RIRS = retrograde intrarenal surgery; SFR = stone-free rate; UAS = ureteral access sheath.

The complete SFR at 4 weeks postoperatively was 85.7% (30/35) and 91% (30/33) in the in situ and relocation groups, respectively (p = 0.506) (Table 2). The majority of residual fragments were located in the lower pole and fragments ranged from 3 to 6 mm (Table 2). Ninety-five percent of patients were discharged by the 1st postoperative day. Overall, Clavien Grade II complication occurred in 3 patients (Table 2). Among those with residual stones, a patient in the in situ group required re-RIRS at 2 months after being symptomatic.

Discussion

The lower pole remains a challenging location during RIRS to access the calculus and perform efficient lithotripsy due to its unfavorable anatomic factors and compromised ureteroscope deflection with the laser fiber in the working channel.¹³ Although recent innovations in the deflection mechanism, ergonomics and durability of ureteroscopes, stone baskets, and use of thinner laser fibers have made lower pole stones more accessible with more efficient lithotripsy, spontaneous passage of stone fragments from the lower calix can still be compromised due to its dependent location.^13,14,19,20

Improvement in SFRs with relocation of lower pole calculi to a more favorable location before lithotripsy has been reported.^11,13 In the present study, with comparable stone size, there was a slightly better overall stone-free trend in patients with relocation followed by lithotripsy (92%) than with in situ lithotripsy (85.7%), although it was not statistically significant.

Similar findings were reported by Kourambas et al as they demonstrated nonsignificant higher SFRs in the relocation group than in the in situ lithotripsy group (90% vs 83%); however, the stones were smaller in the relocation group.¹² Schuster et al also reported significantly higher SFRs in the relocation group compared with the in situ lithotripsy group (relocation 89% vs 77% in situ).¹³

Relocation converts a lower pole stone to nonlower pole stone by moving it to a favorable location. Additionally, due to improved visualization and easier manipulation of the ureteroscope, the ability to perform efficient lithotripsy is enhanced.^10
–12 Relocation of the calculus reduces the likelihood of unintentionally leaving stone fragments that have fallen out of the ureteroscope's view and are inaccessible with retrograde flexion.¹³ This would also circumvent the unfavorable anatomy and dependent location issues, thus facilitating spontaneous passage of fragments.^7,21

A significantly higher SFR was reported by Schuster et al in the relocation group for stones larger than 1 cm (relocation 100% vs 29% in situ).¹³ In our study, we did not find differences in SFRs when stones were categorized into subgroups of <10 mm, 10 to 15 mm, and 15 to 20 mm. Similar to the study by Schuster et al, majority of the stones were relocated to the upper pole, followed by the interpolar region.¹³

In a study by Gallante et al, the total surgery time (median 77.5 vs 53 minutes, p < 0.005) and total laser energy (median 3.6 vs 0.70 J, p < 0.049) were higher in the relocation group; however, a higher stone burden was observed in the relocation group and active retrieval of the relocated fragments was also performed.¹¹ Schuster et al also reported a longer operative duration in the relocation group for stones as large as 15 mm; however, a higher mean stone size in the relocation group may have contributed to the longer duration in their study.¹³

In contrast to the above findings, no differences in operative duration, total lasing energy used, and lasing duration were observed between the groups in our study. The similar operative duration in spite of the time taken to basket and relocate fragments to other poles in the relocation group may be due to the difficulty in ergonomics and effective lithotripsy in the in situ group.

In our study, KUB and ultrasound KUB were used to assess the SFR at 4 weeks and the overall SFR was 88% (53/60), which was comparable with other studies.^8,14,22 There is substantial variation in the reported SFRs due to variation in the definition of stone-free status and in the timing and type of imaging modality.

In a review by Ghani and Wolf, analyzing outcomes of 1069 patients undergoing ureteroscopy, the mean SFR was 84.5% (range 57%–97%); however, the mean zero fragment rate was 51% (range 35%–60%) in studies using CT for assessment of fragments.¹⁴ The better stone-free status even in the in situ group in our study could be due to the use of a high-power laser with the facility of pop-dusting and dusting with generation of finer dust particles, thus facilitating spontaneous passage.

In our study, the complication rates were similar between the groups and most of them were Clavien Grade I complications, with fever being the most common complication. Our complication rate was comparable with those reported by Schuster et al and de la Rosette et al.^5,13 In our study, one patient in the in situ group required second-stage RIRS after becoming symptomatic. In spite of relocation, two patients still had residual fragments in the lower pole calix, which again emphasizes the dependent nature of the lower pole. Stone fragments even less than 4 mm have been associated with a higher rate of stone-related complications, stone growth rate, and interventions.²³

In addition to improving SFRs, relocation potentially reduces the damage to the ureteroscope by minimizing the duration of maximum ureteroscope deflection in the lower pole and reducing laser fiber failure.^7,24 The relocation also reduces surgeon fatigue, arm tremors, and chronic motion injury due to the need to bend the ureteroscope for near maximal flexion and rotation, which in the long run would be detrimental to the surgeon.²⁵

Various techniques have been studied to enhance SFRs in lower pole stones. Mechanical percussion, inversion and diuresis, and external physical vibration lithecbole have also been shown to improve SFRs following flexible ureteroscopy for lower pole stones by relocating the lower pole fragments.^26,27 However, the absence of a uniform protocol regarding these techniques has limited their widespread acceptance.

The best option for management of lower pole calculi is still not known. Surgeon's experience, available instruments, and the patient's preference are important considerations for selection of the procedure. Miniaturization of percutaneous nephrolithotomy (PCNL) has made it a feasible option for management of renal stones even less than 1 cm. Micro-PCNL for lower pole stones has been shown to improve SFRs, but with longer hospital stay, prolonged fluoroscopic duration, and greater decrease in hemoglobin postoperatively compared with RIRS.^28,29

The single-use flexible ureteroscope seems to be comparable with conventional ureteroscopes in terms of visibility and manipulation with no concern for durability; however, in countries such as Nepal, affordability of the single-use ureteroscope is still an issue especially in government hospitals where patients have to bear the cost out of their pocket. Hence, the reusable flexible ureteroscope is likely to remain one of the major components in renal stone management.

There are some limitations of the study. KUB and USG-KUB were used to assess SFRs, which have the possibility of overestimating and underestimating residual fragments compared with CT; however, we still think that the use of CT is impractical due to added radiation exposure and cost.³⁰ All the surgeries were performed in a single center by an experienced surgeon, which limits the generalizability of results.

The follow-up duration of the study was 3 months and assessment of long-term results with longer follow-ups would have been desirable. In cases of smaller stones, the usage of a basket for retrieval of few fragments for stone evaluation may contribute to bias in relation to stone clearance. A cost-effective analysis regarding the use of a basket and repair of damaged ureteroscopes was not done in this study.

Conclusions

Relocation of lower pole stones less than 2 cm in diameter was associated with SFRs that were comparable with in situ lithotripsy, following RIRS, with similar operative and lasing duration and the benefit of better surgeon ergonomics. Multicentric studies with a larger sample are warranted to further validate our findings.

Footnotes

Authors' Contributions

All the authors contributed equally to the work.

Author Disclosure Statement

The authors declare that they have no conflicts of interest.

Funding Information

This was an independent study and it was not funded by any external body.

Abbreviations Used

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