Definition and Unfavorable Risk Factors of Trifecta in Mini-Percutaneous Nephrolithotomy

Abstract

Objectives:

In performing mini-percutaneous nephrolithotomy (PCNL), we aimed at achieving the trifecta of stone-free status and no complications in a single treatment session. We analyzed our experience to determine negative predictors for achieving these three-fold goals.

Patients and Methods:

The data of all consecutive patients who underwent tubeless mini-PCNL between July 2015 and March 2020 in two hospitals were retrospectively reviewed. Stone-free was defined as no residual stones. Complications were recorded and graded according to modified Clavien classification. Patients were divided into two groups according to the outcome (trifecta and non-trifecta). Factors affecting the outcome were compared between both groups by using univariate and multivariate analyses to detect independent unfavorable risk factors.

Results:

The study included 944 patients with mean age 40.2 years (standard deviation: 13.6). The stone-free rate after one session of mini-PCNL was 90.7%. Auxiliary procedures were needed in 14 patients (1.5%). Complications were observed in 76 patients (8.1%). Trifecta was achieved in 792 patients (84%). Independent unfavorable risk factors in multivariate analysis were number of caliceal groups affected by the stones (relative risks were 1.95 to 2.27 and 5.7 for one, two, and three caliceal groups respectively) and number of percutaneous tracts (relative risk was 2.2). Stone size and complexity were not significant predictors of missing trifecta in multivariate analysis.

Conclusions:

Mini-PCNL can achieve a high rate of trifecta (84%) for different stone sizes and complexities. Stones distribution in multiple caliceal groups and multiple tracts are the independent unfavorable risk factor.

Introduction

Standard percutaneous nephrolithotomy (PCNL) is the recommended treatment for large and complex renal stones by major international guidelines.^1,2 Continuous improvements in techniques, instruments, and technology have resulted in increasing safety and efficacy of PCNL. Miniaturization of PCNL such as mini, super-mini, ultra-mini, and micro-PCNL were adopted by many urologists all over the world.³ The main advantages of these techniques are lower morbidity in comparison with standard PCNL.⁴ Moreover, decreasing the size of the nephrostomy tract encouraged utilization of these techniques as an alternative to retrograde intra-renal surgery (RIRS) in the treatment of proximal ureteric calculi.⁵

Mini-PCNL implied utilization of a percutaneous tract of <22F. At first, it was thought that mini-PCNL is suitable for small-sized renal stones.⁶ With increasing experience and refinement of the technique, mini-PCNL was proved to be comparable with standard PCNL for the treatment of large renal calculi more than 20 mm.^7,8 It was also used for the treatment of complex and staghorn stones.^9
–11 The comparable success of mini-PCNL to standard PCNL was accompanied by lower incidence and severity of complications, less postoperative pain, and shorter hospital stay.¹² On the other hand, mini-PCNL was reported to be superior to RIRS in achieving stone-free rates in a single session.¹³

Standardization of outcome evaluation after stone treatment is lacking, especially when comparing two techniques or more.¹⁴ For example, the definition of stone-free rate is still controversial. Inspired by the trifecta criteria for evaluating the outcome of radical prostatectomy¹⁵ or partial nephrectomy,¹⁶ we developed a trifecta criteria for mini-PCNL outcome.

This study was conducted to evaluate trifecta for mini-PCNL and determine unfavorable risk factors.

Patients and Methods

The study protocol was waived from IRB approval because it is a retrospective data analysis without patients' identification.

The computerized data of patients who underwent mini-PCNL between July 2015 and March 2020 in two hospitals were retrospectively reviewed. Preoperative workup included routine laboratory tests (urine analysis and culture, complete blood count, prothrombin time, and serum creatinine). Non-contrast CT (NCCT) was the radiological investigation of choice to evaluate stone burden, distribution in the pelvi-caliceal system, and perirenal anatomy. Mini-PCNL was performed for patients with renal or proximal ureteric stones according to major guidelines unless there were contraindications (such as coagulopathy, uncontrolled hypertension, or untreated urinary tract infection). All consecutive cases who underwent mini-PCNL were included in this study.

Technique of mini-PCNL

All cases were performed in prone position under the effect of spinal anesthesia, except for children or patients who refused spinal anesthesia. After insertion of a 5F ureteric catheter, fluoroscopic guide access was performed to the desired calix. A supracostal middle caliceal puncture was chosen for proximal ureteric, renal pelvis, middle calix, and staghorn stones. Upper or lower caliceal punctures were selected for other renal stones. The tract was dilated to 16–20F by using a plastic single-step dilation set, and a peel-away sheath was placed. Nephrolithotomy was performed through a 12F rigid nephroscope (MIP-M; Karl Storz Endoskope, Tuttlingen, Germany), and a pneumatic lithotripsy was used for stone fragmentation. Evacuation of the fragments was continuously achieved throughout the procedure by vacuum cleaner effect and injection of saline through the ureteric catheter. After visualization of the calix and the upper ureter with the nephroscope to make sure that there are no residual fragments, an antegrade ureteric stent was introduced and the peel-away sheath was removed under direct vision without placement of a nephrostomy tube (tubeless).

Outcomes evaluation

Stone-free status was evaluated after 1 day with plain X-ray film of kidney, ureter, and bladder radiograph or low-dose NCCT. Stone-free was defined as no residual stones. Complications were recorded and graded according to modified Clavien classification. Trifecta was defined as stone-free outcome without complications after a single session of mini-PCNL.

Detecting unfavorable risk factors

Patients were divided into two groups according to the outcome (trifecta and non-trifecta). Non-trifecta group included patients who had residual stones, complications or underwent more than one session of mini-PCNL or auxiliary procedure. Potential factors that may affect the outcome were compared between both groups. Preoperative factors included age, gender, presence of renal anomalies, serum creatinine, preoperative urine culture, stone length, side, burden (single, multiple, or staghorn), Guy's stone score, and number of caliceal groups affected by the stones. Stone length was the maximum diameter of the stone as measured in axial, coronal, and sagittal NCCT. Number of affected calices was zero for ureteric and renal pelvic stones, one for affection of one major caliceal group, two for two groups, and three for affection of all the major caliceal groups (upper, middle, and lower). Tested operative factors were number of percutaneous tracts (single or multiple), site of skin puncture (subcostal, supracostal or both), and tract size (16, 18, or 20F).

Statistical analysis

Patients' data were statistically analyzed by using SPSS v20 software (IBM SPSS Statistics, Armonk, NY). Factors affecting the outcome were compared between both groups by using univariate (chi-square or t-test) and multivariate (binary logistic regression) analyses to detect unfavorable risk factors. P value <0.05 was set for statistical significance.

Results

The study included 944 consecutive patients. The age range was 2–84 years, with 23 of them younger than 18 years. Preoperative demographics, renal and stone characteristics are presented in Table 1. Renal anomalies in 29 patients included duplex system in 11, horseshoe in 11, malrotation in 4, and polycystic kidney in 3. General anesthesia was required in 86 patients (9%). Median operative time was 40 minutes (range 30–180). A 12F nephrostomy tube was placed in eight patients (0.8%). Ureteric stent placement was omitted in another 28 patients (3.2%).

Table 1.

Preoperative Demographics, Renal and Stone Characteristics

Variable	Mean	SD
Age (years)	40.2	13.6
BMI (kg/m²)	29.2	5.5
Creatinine (mg/dL)	0.85	0.26
Longest stone diameter (mm)	18.2	9
Stone density (HU)	1027	295
Variable	n	%
Gender
Male	660	70
Female	284	30
Side
Right	476	50.4
Left	468	49.6
Renal anomalies	29	3.1
Hydronephrosis
No	339	35.9
Yes	605	64.1
History of stone surgery	60	6.4
Guy's score
I	263	27.9
II	513	54.3
III	117	12.4
IV	51	5.4

BMI = body mass index; SD = standard deviation.

Postoperative NCCT was done for 135 patients (14.3%). The stone-free rate after one session of mini-PCNL was 90.7%, as 88 patients (9.3%) had residual stones. Auxiliary procedures for management of residual stones were needed in 14 patients in the form of a second session of mini-PCNL in 9 patients, flexible ureteroscopy in 5. Follow-up was elected for other patients with residual stones.

Complications were observed in 76 patients (8.1%). Modified Clavien grading of complications and their treatment are presented in Table 2. Perforation of the renal pelvis in five patients was treated conservatively because antegrade fixation of a ureteric stent was routinely done for all patients. Blood transfusion was needed in 19 patients (2%). Shock necessitating intensive care unit (ICU) admission was reported in two patients. One of them had severe intraoperative bleeding that was managed with exploration and suturing the bleeding renal parenchyma. The other patient had septic shock that was treated with vasopressors and antibiotics. No cases of mortality were observed. Median hospital stay was 2 days (range 1–14).

Table 2.

Modified Clavien Classifications of Mini-Percutaneous Nephrolithotomy Complications

Complication grade	Treatment	n	%
Grade I		31	3.3
Transient fever >38°	Conservative	19
Perforation of the renal pelvis	Conservative	5
Perinephric hematoma	Conservative	3
Pleural effusion	Conservative	2
Perinephric urinoma	Conservative	1
Spinal headache	Conservative	1
Grade II		24	2.5
Febrile UTI	Antibiotics	10
Bleeding or hematuria	Blood transfusion	14
Grade IIIa		19	2
Severe stent symptoms	Removal of the stent	9
Upper tract obstruction	Exchange of the stent	3
Downward stent migration	Exchange of the stent	2
Hematuria	Embolization and blood transfusion	2
Hydrothorax	Intercostal tube	2
Urinary leakage	Exchange of the stent	1
Grade IVa		2	0.2
Hypovolemic shock	ICU admission and blood transfusion	1
Septic shock	ICU admission and antibiotics	1

Antibiotics other than prophylaxis.

ICU = intensive care unit; UTI = urinary tract infection.

Trifecta was achieved in 792 patients (84%), whereas non-trifecta was observed for 152 patients (16%). Twelve patients had more than one criterion of non-trifecta. Preoperative and operative unfavorable risk factors are summarized in Tables 3 and 4. Independent risk factors for non-trifecta in multivariate analysis were number of caliceal groups affected by the stones and number of percutaneous tracts (Table 5).

Table 3.

Univariate Analysis of Preoperative Factors Affecting Trifecta of Mini-Percutaneous Nephrolithotomy

Categorical variables	Trifecta achieved n (%)	Trifecta missed n (%)	p^a
	792 (84)	152 (16)
Gender			0.410
Male	558 (84.5)	102 (15.5)
Female	234 (82.4)	50 (17.6)
Side			0.676
Right	397 (83.4)	79 (16.6)
Left	395 (84.4)	73 (15.6)
Stone site			<0.001
Proximal ureter	133 (93)	10 (7)
Renal pelvis	279 (90)	31 (10)
Lower calix	123 (85.4)	21 (14.6)
Middle calix	21 (80.8)	5 (19.2)
Upper calix	24 (75)	8 (25)
Pelvis and caliceal	139 (72)	54 (28)
Ureter and caliceal	41 (85.4)	7 (14.6)
Multiple caliceal	32 (66.7)	16 (33.3)
Number of affected calices			<0.001
No	430 (90.3)	45 (9.5)
One	205 (82.7)	43 (17.3)
Two	127 (77.4)	38 (23)
Three	30 (53.6)	26 (46.4)
Renal anomalies			0.865
No	768 (84)	147 (16)
Yes	24 (82.2)	5 (17.2)
Stone burden			<0.001
Single	529 (89)	65 (11)
Multiple	206 (77.7)	59 (22.3)
Staghorn	67 (70.5)	28 (29.5)
Recurrent stones			0.993
No	739 (83.6)	145 (16.4)
Yes	53 (83.3)	7 (11.7)
Preoperative urine culture			0.069
Sterile	761 (84.4)	141 (15.6)
Infected	31 (73.8)	11 (26.2)
Guy's stone score			<0.001
1	232 (88.2)	31 (11.8)
2	439 (85.6)	74 (14.4)
3	92 (78.6)	25 (21.4)
4	29 (57)	22 (43)
Stone length			<0.001
<20 mm	562 (87.7)	79 (12.3)
20–39 mm	208 (78.2)	58 (21.8)
40 mm or more	22 (59.5)	15 (40.5)
Continuous variables	Mean (SD)	Mean (SD)	p^b
Age in years	40.5 (13.6)	39.1 (13.5)	0.260
Creatinine	0.84 (0.28)	0.87 (0.21)	0.738

Chi-square test.

Independent-sample t-test.

Table 4.

Univariate Analysis of Operative Factors Affecting Trifecta of Mini-Percutaneous Nephrolithotomy

Categorical variables	Trifecta achieved n (%)	Trifecta missed n (%)	p^a
	792 (84)	152 (16)
Percutaneous tracts			<0.001
Single	739 (86.3)	117 (13.7)
Multiple	53 (60.2)	35 (39.8)
Skin puncture			<0.001
Subcostal	422 (86)	68 (14)
Supracostal	335 (85)	59 (15)
Both sub- and supracostal	35 (58.3)	25 (41.7)
Tract size			0.051
16F	13 (86.7)	2 (13.3)
18F	772 (84.2)	145 (15.8)
20F	7 (58.3)	5 (41.7)
Number of tracts			<0.001
Single	738 (83.3)	117 (13.7)
Multiple	54 (60.7)	35 (39.3)

Chi-square test.

Table 5.

Multivariate (Logistic Regression) Analysis for Factors Predicting Non-trifecta for Mini-Percutaneous Nephrolithotomy

Independent risk factor	Relative risk	p	95% confidence interval (lower–upper)
Number of affected calices
No (Reference)
One calix	1.95	0.004	1.24–3.06
Two calices	2.27	0.002	1.37–3.79
Three calices	5.70	<0.001	2.92–11.12
Percutaneous tract number
Single (Reference)
Multiple	2.22	0.004	1.29–3.82

Discussion

This study introduces a novel definition of trifecta for mini-PCNL. From the patients' perspective, trifecta of urolithiasis treatment means to become stone-free without complications after a single session of intervention. From the physicians' point of view, these criteria are the ideal scenario because they alleviate the need for secondary procedures to achieve stone-free status or manage complications in addition to shorter hospital stay with reduction of total costs. In the present study, these trifecta criteria were met in 84% of patients who underwent mini-PCNL.

Independent significant factors for not having trifecta were the presence of stones or branches in multiple calices and utilization of more than one tract. These two factors are related to each other, as stones in different calices may require multiple punctures to achieve complete clearance. It was observed also that increasing the number of involved calices from one to two or three led to an increase in the relative risk for missing trifecta from 1.95 to 2.27 and 5.7, respectively. A recent article by Harraz and colleagues showed that caliceal stone distribution was a significant predictor of stone-free rate after PCNL.¹⁷ This can be explained by missing some of the stones in calices away from the percutaneous tract or increasing the risks of complications with multiple punctures. Similar results were reported, as the number of caliceal involvement represented risks for complications in standard PCNL.¹⁸ There are contradictory results regarding the safety of multi-tract versus single-tract approach for complex renal stones. Balaji et al. performed a meta-analysis for 10 studies of multiple tracts PCNL. They have found that multi-tract PCNL is safe and cost-effective for complex renal stones.¹⁹ On the contrary, multiple tracts were recorded as a significant risk for severe bleeding requiring angiographic embolization in standard PCNL.^20,21

Some preoperative variables such as stone length, burden, and Guy's score were not significant risks for missing trifecta in multivariate analysis. Such findings highlight the versatility of mini-PCNL regardless stone length, burden (single, multiple, or staghorn) or Guy's score. Utilizing mini-PCNL for the treatment of large renal stones is another controversial issue in urological literature. Some reported that the stone-free rate of mini-PCNL for stones larger than 20 mm was inferior to standard PCNL.^6,22 On the other hand, a recent multicenter randomized controlled study with a large number of patients showed that mini-PCNL is not inferior to standard PCNL in the treatment of 20–40 mm renal stones.⁸ However, in a meta-analysis, Feng and associates found no difference in stone-free rates between standard and mini-PCNL for stones larger than 2 cm.²³ Moreover, mini-PCNL was proved to be an effective modality in the treatment of complex and staghorn stone,^10,24 which is coinciding with the results of the present study.

Comparing different endourological techniques for the treatment of renal and proximal ureteric stones is a hot topic for research. Standard PCNL achieves the highest stone-free rate in a reasonable operative time at the expense of increased incidence and severity of complications. Thapa and Niranjan conducted a meta-analysis of 19 contemporary studies comparing standard and mini-PCNL. They concluded that the stone-free rates of mini-PCNL were comparable with standard PCNL, with fewer complications apart from that mini-PCNL required a longer operative time.²⁵ RIRS was proved to be safer but less effective than PCNL because of the lower stone-free rate, longer operative time, and need for multiple procedures.²⁶ Mini-PCNL combines the high stone-free rates with lower complications and less need for auxiliary procedures.²⁷ Advances in intracorporeal lithotripsy such as Thulium fiber laser can significantly increase the speed of large stone disintegration and, hence, shorten the operative time.²⁸ We believe that mini-PCNL can be the best treatment of renal and proximal ureteral stones of any size, location, and complexity.

Mini-PCNL is not just miniaturization of standard PCNL. It is a different concept. The most obvious difference is the small tract size that minimizes bleeding. In the present study, the transfusion rate of 2% is comparable with the transfusion rate of 1.4%–8.9% for mini-PCNL and lower than the 5.5%–15.2% for standard PCNL of the meta-analysis done by Feng et al.²³ These rates of blood transfusion were lower than standard PCNL. Moreover, it allows exploring different calices as well as the upper ureter through a single puncture. Another important difference is the method of stone fragment retrieval. In standard PCNL, stone fragments must be seen and then removed by forceps or basket; whereas in mini-PCNL, fragments are continuously evacuated through a vacuum cleaner effect. This mechanism allows effective evacuation of stone fragments from different locations in the different calices. The third difference is the decreased need of placement of a nephrostomy tube with all the advantages of the tubeless (nephrostomy free) technique, such as lower postoperative pain and shorter hospital stay.

This study provides a standardized definition for the outcome of urolithiasis management that can be applicable for any treatment modality. Standardization of outcome evaluation for any surgical intervention is important for comparing different procedures. Another strong point is the application of a strict criterion for stone-free rate (no residual stones of any size). Nevertheless, this study has some limitations. First is the retrospective design that prevented evaluating the effect of some factors such as the patient's comorbidity, body mass index, and renal anatomical features on trifecta outcome as these data were not available for all patients. Second, not all patients had NCCT for evaluation of postoperative stone-free rate. The third limitation was not comparing mini-PCNL with standard PCNL or RIRS. Randomized comparative studies are still needed to confirm the superiority of mini-PCNL over standard PCNL and RIRS in achieving trifecta for upper tract urolithiasis treatment.

Conclusions

Mini-PCNL can achieve a high rate of trifecta (84%) different stone sizes and complexities. Stones' distribution in multiple caliceal groups and multiple tracts are the independent risk factor for missing trifecta.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this work.

Abbreviations Used

References

Assimos

, Krambeck

, Miller

, et al. Surgical Management of Stones: American Urological Association/Endourological Society Guideline, PART II. J Urol, 2016; 196:1161–1169.

Turk

, Petrik

, Sarica

, et al. EAU Guidelines on Interventional Treatment for Urolithiasis. Eur Urol, 2016; 69:475–482.

Ganpule

, Bhattu

, Desai

. PCNL in the twenty-first century: Role of Microperc, Miniperc, and Ultraminiperc. World J Urol, 2015; 33:235–240.

Ruhayel

, Tepeler

, Dabestani

, et al. Tract sizes in miniaturized percutaneous nephrolithotomy: A systematic review from the European Association of Urology Urolithiasis Guidelines Panel. Eur Urol, 2017; 72:220–235.

Gao

, Gao

, Qu

, et al. Minimally invasive percutaneous nephrolithotomy improves stone-free rates for impacted proximal ureteral stones: A systematic review and meta-analysis. PLoS One, 2017; 12:e0171230.

Abdelhafez

, Amend

, Bedke

, et al. Minimally invasive percutaneous nephrolithotomy: A comparative study of the management of small and large renal stones. Urology, 2013; 81:241–245.

Guler

, Erbin

, Ucpinar

, Savun

, Sarilar

, Akbulut

. Comparison of miniaturized percutaneous nephrolithotomy and standard percutaneous nephrolithotomy for the treatment of large kidney stones: A randomized prospective study. Urolithiasis, 2019; 47:289–295.

Zeng

, Cai

, Duan

, et al. Mini percutaneous nephrolithotomy is a noninferior modality to standard percutaneous nephrolithotomy for the management of 20–40 mm renal calculi: A multicenter randomized controlled trial. Eur Urol, 2021; 79:114–121.

Zeng

, Zhao

, Wan

, et al. Minimally invasive percutaneous nephrolithotomy for simple and complex renal caliceal stones: A comparative analysis of more than 10,000 cases. J Endourol, 2013; 27:1203–1208.

10.

Zhao

, Cui

, Zeng

, Wan

, Zeng

. Comparison of 1-stage with 2-stage multiple-tracts mini-percutaneous nephrolithotomy for the treatment of staghorn stones: A matched cohorts analysis. Urology, 2016; 87:46–51.

11.

Khadgi

, El-Nahas

, El-Shazly

, Al-Terki

. Comparison of standard- and mini-percutaneous nephrolithotomy for staghorn stones. Arab J Urol, 2021:1–5. DOI: 10.1080/2090598X.2021.1878670.

12.

Zhu

, Liu

, et al. Minimally invasive versus standard percutaneous nephrolithotomy: A meta-analysis. Urolithiasis, 2015; 43:563–570.

13.

Gao

, Liao

, Chen

, et al. Different tract sizes of miniaturized percutaneous nephrolithotomy versus retrograde intrarenal surgery: A systematic review and meta-analysis. J Endourol, 2017; 31:1101–1110.

14.

Tokas

, Nagele

. Stone free rates (SFRs) after retrograde intrarenal surgery (RIRS) and percutaneous nephrolithotomy (PCNL); are we comparing apples with watermelons?. World J Urol, 2016; 34:1503–1504.

15.

Bianco

Jr. , Scardino

, Eastham

JA.

Radical prostatectomy: Long-term cancer control and recovery of sexual and urinary function (“trifecta”). Urology, 2005; 66:83–94.

16.

Zargar

, Porpiglia

, Porter

, et al. Achievement of trifecta in minimally invasive partial nephrectomy correlates with functional preservation of operated kidney: A multi-institutional assessment using MAG3 renal scan. World J Urol, 2016; 34:925–931.

17.

Harraz

, El-Nahas

, Nabeeh

, et al. Development and validation of a simple stone score (SSS) to estimate the probability of residual stones prior to percutaneous nephrolithotomy. Minerva Urol Nefrol, 2020 [Epub ahead of print]; DOI: 10.23736/S0393-2249.20.04055-2.

18.

El-Nahas

, Nabeeh

, Laymon

, Sheir

, El-Kappany

, Osman

Preoperative risk factors for complications of percutaneous nephrolithotomy. Urolithiasis, 2020 [Epub ahead of print]; DOI: 10.1007/s00240-020-01203-9.

19.

Balaji

, Ganpule

, Herrmann

, Sabnis

, Desai

. Contemporary role of multi-tract percutaneous nephrolithotomy in the treatment of complex renal calculi. Asian J Urol, 2020; 7:102–109.

20.

El-Nahas

, Shokeir

, El-Assmy

, et al. Post-percutaneous nephrolithotomy extensive hemorrhage: A study of risk factors. J Urol, 2007; 177:576–579.

21.

, Wu

, Liu

, et al. Risk factors for hemorrhage requiring embolization after percutaneous nephrolithotomy: A meta-analysis. Transl Androl Urol, 2020; 9:210–217.

22.

Kokov

, Manka

, Beck

, et al. Only size matters in stone patients: Computed tomography controlled stone-free rates after mini-percutaneous nephrolithotomy. Urol Int, 2019; 103:166–171.

23.

Feng

, Hu

, Tang

, Han

, Wei

. The efficacy and safety of miniaturized percutaneous nephrolithotomy versus standard percutaneous nephrolithotomy: A systematic review and meta-analysis of randomized controlled trials. Investig Clin Urol, 2020; 61:115–126.

24.

Guohua

, Zhong

, Li

, et al. Minimally invasive percutaneous nephrolithotomy for staghorn calculi: A novel single session approach via multiple 14–18Fr tracts. Surg Laparosc Endosc Percutan Tech, 2007; 17:124–128.

25.

Thapa

, Niranjan

. Mini PCNL over standard PCNL: What makes it better?. Surg J, 2020; 6:e19–e23.

26.

Palmero

, Durán-Rivera

, Miralles

, Pastor

, Benedicto

. Comparative study for the efficacy and safety of percutaneous nefhrolithotomy (PCNL) and retrograde intrarenal surgery (RIRS) for the treatment of 2–3.5 cm kidney stones [Estudio comparativo de eficacia y seguridad de la nefrolitotomía percutánea (NLPC) y la cirugía retrógrada intrarrenal (CRIR) para litiasis renales de 2–3.5 cm]. Arch Esp Urol, 2016; 69:67–72.

27.

Zhao

, Sun

, Zeng

, Deng

, Liu

, Zeng

. An easy risk stratification to recommend the optimal patients with 2–3 cm kidney stones to receive retrograde intrarenal surgery or mini-percutaneous nephrolithotomy. Urolithiasis, 2020; 48:167–173.

28.

Enikeev

, Taratkin

, Klimov

, et al. Thulium-fiber laser for lithotripsy: First clinical experience in percutaneous nephrolithotomy. World J Urol, 2020; 38:3069–3074.