Flank-Free Modified Supine vs Prone Ultra-Mini-Percutaneous Nephrolithotomy in Treatment of Medium-Sized Renal Pelvic Stone: A Randomized Clinical Trial

Abstract

Introduction and Objectives:

Percutaneous nephrolithotomy (PCNL) is the standard treatment of renal stone >2 cm. Ultra-mini-percutaneous nephrolithotomy (UMP) had emerged in the past decade as a new technique in treating renal stones <2 cm. In this study we compared between the outcome of UMP in prone position with the outcome of UMP in modified flank free supine position (FFSP).

Materials and Methods:

A prospective randomized study was conducted between January 2016 and April 2020, including 122 patients, divided into two matched groups. Group A included 61 patients who underwent UMP in FFSP, and Group B included 61 patients who underwent UMP in a prone position. All patients had a single renal pelvic stone 1–2 cm. Patients with a single kidney, renal anomalies, body mass index ≥40 kg/m², history of ipsilateral renal surgery, and age <18 years were excluded. In both groups, the dilatation was done up to 13F; a holmium laser was used through a 9F ureteroscope for fragmentation. Nephrostomy tube and ureteral stent were used only when indicated.

Results:

In total, 122 patients were divided into two groups. The mean age was 40.09 ± 13.63 and 39.67 ± 13.80 years in both groups, respectively. The operative time was 63.64 ± 9.22 and 78.48 ± 9.55 minutes in Groups A and B, respectively (p = 0.0001). The fluoroscopy time was 3.47 ± 0.56 and 4.45 ± 0.39 minutes in Groups A and B, respectively (p = 0.0001). No significant difference was shown between both groups regarding operative and postoperative complications. Shift to mini-PCNL was needed in one patient in Group A and four patients in Group B because of impaired vision. The hospital stay was 25.36 ± 4.23 and 26.13 ± 4.76 hours in both groups, respectively. The initial stone-free rate was 95.1% and 91.8% in both groups, respectively.

Conclusions:

UMP in modified supine position shows comparable results with UMP in the prone position regarding stone-free rate, hospital stay, and perioperative complication, with significantly shorter operative and fluoroscopy time

Introduction

Percutaneous nephrolithotomy (PCNL) has gained wide popularity since its first description by Fernstrom and Johanson.¹ Now, PCNL is the first treatment option for managing renal calculi >2 cm.² Many modifications in the conventional PCNL emerged in the past two decades to improve the outcomes of the technique and minimize the complication rate.³ The supine position had been described by Valdivia in 1987 and reported in his study that this position provides lower renal pelvic pressure, the ability of simultaneous antegrade and retrograde intervention, and easy management of the respiratory system by the anesthetist.⁴

Modified flank free supine position (FFSP) was described for the first time by Desoky et al..⁵ Intraoperative bleeding during PCNL is the most critical risk facing the urologist and is usually attributed to the size and number of tracts used to access the renal stone.⁶ Miniperc procedure had been described for the first time by Jackman and coworkers⁷ who used a semirigid ureteroscope within its sheath. Ultra-mini-percutaneous nephrolithotomy (UMP) is a newly developed technique described by Desai and Solanki.⁸ A 3–5F ultrathin telescope is used through a specially designed sheath admitted after dilatation of the tract up to 13F.⁸ The purpose of our study is to compare results of UMP in a prone with UMP in modified FFSP.

Patients and Methods

After obtaining the approval of our internal institutional review board, 122 patients with a single renal pelvic stone ranging from 1 to 2 cm had been included in our study from January 2016 to April 2020.

The exclusion criteria were:

Patients with a single kidney

Patients aged <18 years

Patients with body mass index (BMI) ≥40 kg/m²

Patients with renal or skeletal anomalies

Patients with a history of ipsilateral renal surgery.

The patients were divided into two equally matched groups. Group A included 61 patients who underwent UMP in FFSP, and Group B included 61 patients who underwent UMP in a prone position.

Preoperative preparation

Written informed consent was obtained from all patients.

Complete history taking regarding present illness, previous surgery, and any associated comorbidities.

Physical examination with special attention toward any skeletal problems and BMI.

Laboratory investigation in the form of complete blood count, liver and kidney function tests, coagulation profile, urinalysis, and urine culture.

Noncontrast CT to measure the stone size in its greatest dimension and stone density.

Second-generation cephalosporin was introduced to all patients just before induction of anesthesia.

Operative technique

The posterior axillary line was marked in all patients before induction of anesthesia, and then the patients were put in lithotomy position; 5F open tip ureteral catheter was introduced retrogradely under c-arm guidance. The patients in Group A were put in a modified FFSP by putting a cushion under the chest and buttock, making the flank free, whereas patients in Group B were put in a prone position.

Opacification of the system was done by retrograde pyelography, 18-gauge Boston scientific percutaneous needle was passed into the desired calix under c-arm guidance, and then 0.07112 cm sensor wire with the hydrophilic end was introduced into the ureter in most cases or the pelvis or upper calix. Fascial dilators were used for gradual dilatation of the tract up to 13F. Central Alken was inserted, and the sheath was inserted over it till reaching the desired calix. A semirigid 9F ureteroscope was inserted into the sheath and holmium yttrium aluminum garnet laser using a 200 μm holmium laser fiber with the setting of 10–20 W was used for stone dusting and fragmentation. Grasper forceps and/or Dormia basket were used for stone fragment removal.

At the end of the procedure, retrograde pyelography was done to ensure the integrity of the pelvicaliceal system.

A nephrostomy tube was inserted in the minority of cases in whom the tube is mandatory, such as significant bleeding, pelvicaliceal system perforation, or residual fragments, which may need a second look, otherwise tubeless PCNL was the main procedure in most cases.

Ureteral Double-J stent was inserted only if there was bleeding, residual stone, or ureteral stricture; otherwise, the ureteral catheter was left for 24–48 hours and then removed. The operative time was calculated from ureteral catheter insertion till nephrostomy tube positioning or skin closure in tubeless cases.

Postoperative evaluation

Monitoring the blood pressure and complete blood count is mandatory for all patients on the first day postoperatively. The nephrostomy tube was removed 24 hours postoperatively after carrying out kidney, ureter, and bladder radiograph, and the ureteral catheter was removed 24–48 hours after the procedure. Noncontrast CT was done for all patients after 1 month to detect the stone-free rate.

Statistical analysis

The collected data were computerized, statistically analyzed, and presented by tables using Statistical Package for the Social Sciences (SPSS) software version 25. To determine the distribution characteristics of variables and variance homogeneity, Kolmogorov–Smirnov and Levene tests were used. Frequencies and percentages were used to reflect descriptive data. Mean and standard deviation were used to summarize quantitative results. Comparison between Group A and Group B was done using the appropriate tests of significance. Chi-squared test (χ ²) and Fisher exact test were used to compare categorical variables. Student's t-test was used to compare between continuous variables. p-Value <0.05 was considered statistically significant

Results

Our study included 122 patients who were divided randomly into two matched groups. Group A included 61 patients who underwent UMP in FFSP, and Group B included 61 patients who underwent UMP in a prone position. The patient's demographic data are summarized in Table 1, which showed that the mean age of both groups was 40.09 ± 13.63 and 39.67 ± 13.80 years, respectively. There was no significant difference between the groups regarding gender, BMI, and associated comorbidities.

Table 1.

Patients Demographic Data and Stone Characteristics

	Group A	Group B	Test of significance	p
Patient characteristics
Age	40.09 ± 13.63	39.67 ± 13.80	t = 0.169	0.866
Gender
Male	34	32	χ ² = 0.132	0.716
Female	27	29
BMI (kg/m²)	28.2 ± 3.4	27.5 ± 3.1	t = 2.207	0.029
Associated comorbidity
DM	5 (%)	4 (%)	χ ² = 0.424	0.935
HPN	9	8
Cardiac	3	4
Others	4	5
Stone characteristics
Size (mm)	15.1 ± 3.5	14.8 ± 2.9	t = 0.516	0.607
Stone density (HU)	810.1 ± 49.07	795.07 ± 55.27	t = 1.588	0.115

BMI = body mass index; DM = diabetes mellitus; HPN = hypertension.

Table 2.

Operative Data and Postoperative Outcomes

	Group A	Group B	Test of significance	p
Operative side
Right	28	30	χ ² = 0.132	0.717
Left	33	31
Access, n (%)
Lower calix	49 (80.3)	45 (73.8)
Middle calix	10 (16.4)	11 (18.1)	χ ² = 1.504	0.472
Multiple	2 (3.3)	5 (8.1)
Bleeding need transfusion, n (%)	1 (1.6)	2 (3.3)	χ ² = 0.342	0.559
Shift to mini-PCNL, n (%)	1 (1.6)	4 (6.4)	χ ² = 1.877	0.171
Tubeless procedure, n (%)	45 (73.8)	40 (65.6)	χ ² = 0.969	0.325
Operative time (minutes), mean ± SD	63.64 ± 9.22	78.48 ± 9.55	t = 8.731	0.0001^*
Fluoroscopy time (minutes), mean ± SD	3.47 ± 0.56	4.45 ± 0.39	t = 11.216	0.0001^*
Postoperative complications, n (%)
Grade I	5 (8.1)	7 (11.4)	χ ² = 0.754	0.860
Grade II	2 (3.3)	2 (3.3)
Grade IIIa	1 (1.6)	2 (3.3)
Double-J placement, n (%)	6 (9.8)	9 (14.7)	χ ² = 0.684	0.409
Hospital stay (hours), mean ± SD	25.36 ± 4.23	26.13 ± 4.67	t = 0.954	0.342
Stone-free rate, %
Initial	95.1	91.8	χ ² = 0.535	0.464
1 month	98.4	96.7	χ ² = 0.342	0.559

PCNL = percutaneous nephrolithotomy; SD = standard deviation.

Stone size was 15.1 ± 3.5 and 14.8 ± 2.9 cm in Groups A and B, respectively. The stone density was 810.1 ± 49.07 and 795.07 ± 55.27 HU in both groups, respectively. The operative time in Group A and Group B was 63.64 ± 9.22 minutes and 78.48 ± 9.55 minutes, respectively.” The fluoroscopy time was 3.47 − 0.56 minutes in Group A and it was 4.45 − 0.39 minutes in Group B.

Bleeding necessitates blood transfusion and was reported in one patient in Group A (1.6%) and two patients (3.3%) in Group B with no significant difference. Lower calix was the most common access to a kidney stone in 49 patients (80.3%) in Group A and 45 patients (73.8%) in Group B. Multiple access was needed in two patients (3.3%) and five patients (8.1%) in Groups A and B, respectively. In our study, a nephrostomy tube was inserted only if there is significant bleeding, impaired vision, or drop in patient blood pressure or residual fragments are present.

The tubeless procedure was detected in 45 patients (73.8%) and 40 patients (65.6%) in Groups A and B, respectively. Postoperative Double-J stent insertions were reported in six (9.8%) and nine patients (14.7%) in both groups, respectively. The postoperative complications were categorized according to the modified Clavien–Dindo classification system and showed no stage IV or V complication with no significant difference between groups.⁹ Shift to mini-PCNL was reported in one patient in Group A (1.6%) and three patients in Group B (6.4%), and this was because of impaired vision.

The hospital stay was 25.36 ± 4.23 and 26.13 ± 4.76 hours in Groups A and B, respectively, with no significant difference. The stone-free rate was measured twice: the first measurement was 1 day after operation and was 95.1% and 91.8% in both groups, respectively. The second measurement was 1 month after the procedure and was 98.4% and 96.7% in both groups, respectively, with no significant difference between the two measurements.

Significant residual fragments were detected in three patients in the supine group. One patient needed extracorporeal shock wave lithotripsy (ESWL), the second patient needed ureterorenoscopy, and the third patient needed an asymptomatic lower calix fragment. In contrast, the prone group showed five patients with significant residual fragments: two of them needed ESWL, one patient needed ureterorenoscopy, and the remaining two patients needed no intervention because the residual fragment was 4 mm in the lower calix and nonsymptomatic.

Discussion

Nephrolithiasis is a worldwide problem because of high prevalence in all age groups and high incidence of recurrence.¹⁰

Many strategies are used in the treatment of renal stones, such as open surgery ESWL, flexible ureterorenoscopy, PCNL, and laparoscopic pyelolithotomy in some selected cases.¹¹

Conventional PCNL has gained wide popularity since its first use in 1976¹ and became the first choice of treatment of renal stones >2 cm.^2,12 Miniaturized PCNL emerged in the past two decades depending on the fact that smaller diameter instruments and sheaths lead to a lower incidence of complications, especially parenchymal bleeding.⁶ PCNL was classified according to tract size into standard PCNL, Mini-PCNL and micro-PCNL.

UMP is a novel term used by Desai and coworkers in 2013 when they published their initial experience in performing PCNL using 6F mini-nephroscope through an 11F/13F sheath.¹³ Prone position PCNL was the original method described initially, however, supine PCNL was introduced by Valdivia in 1987 who concluded that supine position is superior to prone position with respect to comfort to the patient, less renal pelvic pressure, simultaneous antegrade and retrograde intervention, and easy access and manipulation of the respiratory system by anesthetist.^4,14,15

The incidence of colonic injuries in the literature shows great variation. In our study, no colonic injury has been reported in both groups, and this matches the results of Duty and associates¹⁶ and Desio et al.,¹⁷ who reported no colonic injuries in their series, but in a study published in 2011 by Valdivia depending on CROES database, the colonic injury was found to be similar in both supine and prone groups (3.4% vs 3.3%).

Boon et al. concluded that anterior displacement of the intestine in a supine position is associated with lower incidence of colonic injury.¹⁸ Bleeding in UMP is minimal because of the small tract size. However, one patient in our study in the supine group (1.6%) and two patients (3.3%) in the prone group needed blood transfusion, and this is less than the results of Ozdemir and coworkers, who carried out a comparative study between supine and prone miniaturized PCNL and reported that blood transfusion was needed in four patients in the supine group (7.4%) and six patients in prone group (5.6%): this may be attributed to small tract size used in our study.¹⁹ Desai and coworkers reported in their study that there was no significant bleeding necessitating blood transfusion.¹³

The overall complication rate was comparable between both groups (13.1%) in Group A and (18.1%) in Group B, and this matches the results of Desai and coworkers, who reported a 16.7% incidence of overall complications. In a comparative study between PCNL, miniperc, and ultraminiperc, the overall complications rate was 13.5%, 4.2%, and 2.4%, respectively.²⁰

The operative time in our study was 63.64 ± 9.22 and 78.48 ± 9.55 minutes in Groups A and B, respectively. The significantly lower operative time in the supine group relative to the prone group is attributed to the time needed for patient repositioning in the prone PCNL. The supine position helps minute fragments to come out spontaneously with washing. These results match the results of many studies comparing supine and prone positions.^17,21,22

In a comparative study by Ozdemir and colleagues, the operative time was 58.1 ± 45.9 and 80.1 ± 40.0 minutes, p = 0.025 in both supine and prone mini-PCNL.¹⁹ Desai and coworkers reported that the operative time was 59.8 ± 15.9 minutes: in their series, ∼35 patients underwent UMP as initial experience for treatment of renal stones <2 cm.¹³

The fluoroscopy time was significantly shorter in the supine group relative to the prone group (3.47 ± 0.56 and 4.45 ± 0.39 minutes), respectively, and this agrees with the results of Ozdemir and colleagues, who reported significant shorter fluoroscopy time in the supine group relative to the prone group who underwent miniaturized PCNL (3.0 ± 1.7 and 4.9 ± 4.5 minutes), respectively.¹⁹

Shift to mini-PCNL was done in one patient in the supine group (1.6%) and four patients (6.4%) in the prone group because of impaired vision by dilatation of the tract up to 16F and introduction of 12F nephroscope to complete the procedure. Desai and coworkers reported no shift to mini-PCNL because only one patient (2.8%) needed a second look UMP because of impaired vision.¹³

The need for a postoperative nephrostomy tube is minimized by decreasing the tract size and is limited only in cases of intraoperative bleeding or residual stone fragment, which may necessitate a second-look procedure. In our study, tubeless UMP was achieved in 45 patients (73.8%) and 40 patients (65.6%) in supine and prone groups, respectively.

These results exceed that of the Ozdemir study, which reported tubeless procedure in 20 patients (37.0%) and 19 patients (17.5%) in supine mini-PCNL and prone mini-PCNL groups, respectively.¹⁹ In our study, the stone-free rate was considered if no fragments were left or small fragments <4 mm were present, and the rate was measured twice: the first measurement was 1 day after the operation, and it was 95.1% and 91.8% in both groups, respectively, with no significant difference. The second measurement was 1 month after the procedure, and it was 98.4% and 96.7% in both groups, respectively.

Our results match that of Desai, who reported an initial stone-free rate of 88.9% and increased to be 97.2% after 1 month and exceeded that of Bozzini and coworkers, who reported stone-free rate in the UMP group to be 78% at 3 months follow-up.²⁰

Limitations

The main limitation of our study was the exclusion of pediatric patients and to avoid heterogeneity of the results, especially type of anesthesia, BMI, and operative time. The second limitation was the lack of stone analysis postoperatively and its impact on stone fragmentation and hence operative time and stone-free rate.

The third limitation was the exclusion of all renal calculi rather than renal pelvic stones. This was to avoid contamination of the results, especially in upper renal calculi, which differ in patient positions, and may need a supracostal approach. Finally, further studies with a large number of patients are needed for comparison and to verify our results.

Conclusions

UMP is a new technique and has gained popularity in patients with renal stones <2 cm when PCNL is required.

UMP in modified FFSP shows results comparable with UMP in prone position regarding perioperative complication and stone-free rate, with significantly shorter operative and fluoroscopy time.

Footnotes

Authors' Contributions

K.A. contributed to conceptualization, methodology, supervision, and validation. M.S.E. was the corresponding author, took charge of software, formal analysis, investigation, and resources. E.D. was involved in data curation, writing original draft, and editing. M.M.S. carried out visualization and project administration. We confirm that all authors have participated in the concept and design, analysis and interpretation of data, drafting or revising the article, and they have approved the article as submitted.

Disclaimer

We confirm that the research contained in the article has not been published and not under consideration elsewhere.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Abbreviations Used

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