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Comparison of the efficacy and safety of mini-percutaneous nephrolithotomy versus retrograde intrarenal surgery for the treatment of kidney stones in overweight or obese patients: a systematic review and meta-analysis

BMC Urology volume 24, Article number: 243 (2024) Cite this article

Abstract

Objective

To discuss the differences in the effectiveness and security of kidney stones in overweight or obese patients by mini percutaneous nephrolithotomy (MiniPCNL) and retrograde intrarenal surgery (RIRS).

Materials and methods

We exhaustively searched numerous databases, including PubMed, Embase, Web of Science, Cochrane Library, and CNKI, covering all records from their initiation date until September 2023. This included controlled trials focusing on the use of MiniPCNL and RIRS in the treatment of kidney stones in overweight or obese patients. The gathered data was then analyzed using the Review Manager 5.4 software.

Results

9 studies including 1122 patients were included. Meta-analysis showed that: The MiniPCNL group had higher overall complications, grade I complications, length of hospital stay(LOS), first stone-free rate (SFR), and final SFR in obese patients, with no significant difference between the two groups in terms of operative time(OT), hemoglobin drop, and grade II complication rate. There were more overall complications, grade I complications, final SFR, and LOS with MiniPCNL in patients with stones > 2 cm compared to no significant difference in grade II complications. MiniPCNL performed in the prone position had higher final SFR, less OT, hemoglobin drop, and no statistically significant difference in overall complications or LOS. Sheaths using > 14 F had higher overall complication rates, final SFR, and LOS, and no statistical differences in OT and first SFR between the two modalities. In the MiniPCNL subgroup aged ≤ 50 years, there were higher first SFR, final SFR, and shorter OT, and in the MiniPCNL subgroup aged > 50 years, there were more OT, LOS, and hemoglobin drop, with no statistical difference in overall complications between the two groups.

Conclusion

Our study showed that MiniPCNL in obese patients had higher initial SFR and final SFR, fewer procedures, but more postoperative complications, LOS, and grade I complications compared with RIRS. Similar results were seen in patients in the prone position, with stones > 2 cm and age ≤ 50 years.

Systematic review registration

[https://www.crd.york.ac.uk/PROSPERO/], identifier PROSPERO (CRD42023467284).

Peer Review reports

Background

Kidney stones are such a prevalent condition that they impact roughly 10% of the global population, with the incidence steadily rising each year [1]. The formation of kidney stones is associated with several factors, and previous studies have reported that elevated body mass index (BMI) is strongly associated with the formation of kidney stones [2,3,4]. Kidney stones are highly susceptible to recurrence, with about 50% of patients having a recurrence after ten years [5, 6]. The European Association of Urology (EAU) categorizes percutaneous nephrolithotomy (PCNL) as the gold-standard treatment for kidney stones larger than 2 cm [7]. In the past, retrograde intrarenal surgery (RIRS) was primarily recommended for treating smaller stones. However, with the evolution of surgical procedures and technologically advanced equipment, RIRS is increasingly being employed to treat renal stones more significant than 2 cm. RIRS has also demonstrated a similar final stone-free rate (SFR) and fewer complications in comparison to PCNL [8, 9]. The current treatment tends to be mini percutaneous nephrolithotomy (MiniPCNL) due to the fear of impaired renal function.

In the pursuit of fewer complications and higher SFR, MiniPCNL has emerged, which can achieve an SFR that is not significantly different from that of standard PCNL and has the advantages of less bleeding and fewer complications than standard PCNL, with the disadvantage of a longer operative time (OT) [10, 11]. Multiple studies have demonstrated statistically significant differences in hemoglobin decline and Length of hospital stay (LOS) in the MiniPCNL group compared to RIRS in populations of obese or overweight patients [12,13,14,15,16,17,18]. However, a prospective multicenter study by Sunil Bhaskara Pillai et al. revealed lower instances of hemoglobin decline and reduced LOS in the MiniPCNL group as compared to the RIRS group [19]. Furthermore, research led by He-Qun Chen et al. disclosed that an increase in BMI which correlated to increased subcutaneous and visceral fat, posed challenges in MiniPCNL access and restricted nephroscope movement, consequently extending OT and decreasing SFR [16]. However, A Meta-analysis shows that for RIRS, OT is largely unaffected in overweight or obese patients [20].

The decision to proceed with MiniPCNL or RIRS in managing kidney stones among overweight or obese patients remains a subject of discussion, consequently leaving medical practitioners to depend on their experiential judgment while selecting surgical approaches. As such, we carried out a systematic evaluation and meta-analysis during our study to confirm the safety and effectiveness of RIRS and MiniPCNL concerning kidney stones treatment in obese and overweight patients, to enhance clinicians’ decision-making process.

Materials and methods

We strictly followed the guidelines set forth by the Preferred Reporting Items for Systematic Evaluation and Meta-Analysis (PRISMA) and also adhered to the Extended Statement on Meta-Analysis [21, 22].

Search strategy

In our research, we conducted a thorough computerized search across 5 databases - PubMed, Web of Science, Cochrane Library, Embase, and CNKI. The aim was to accumulate articles published on the treatment of renal stones in obese or overweight patients via MiniPCNL versus RIRS. This search encompassed the respective databases’ inception timeframe up to September 2023. Moreover, overweight is defined as BMI > 25 kg/m2 and obesity is defined as BMI ≥ 30 kg/m2. The keywords used for the search were RIRS, Obesity, Overweight, MiniPCNL, and nephrolithiasis.

Inclusion and exclusion criteria

Inclusion and exclusion criteria for article screening were established before the literature search began.

Inclusion criteria

Participants

Obese or overweight patients diagnosed with kidney stones.

Interventions and comparisons

Comparison between MiniPCNL and RIRS.

Outcomes

At least one of our data of interest (including basic characteristics (Table 1), first SFR, final SFR, OT, number of operations, LOS, hemoglobin drop, total complications, Clavien grade I and II complications.

Exclusion criteria

Exclusion criteria were as follows

(a) incomplete data; (b) case, review, or conference papers; (c) full text could not be extracted; (d) animal experiments.

Data extraction

The screening of literature and extraction of data was independently carried out by two investigators, following specific inclusion and exclusion criteria. The primary outcome indicators studied in this paper were: first SFR, final SFR, OT, number of procedures, LOS, hemoglobin drop, total complications, and Clavien grade I and II complications. The definition of stone-free status (SFS) was shown differently in several articles, but focused on the finding of no stones or any stone fragments less than 3 mm on postoperative follow-up ultrasound or non-enhanced CT KUB examination; therefore, we defined first SFR as stone-free status on follow-up imaging within 1–3 days postoperatively; and final SFR was the stone-free status on follow-up imaging within 1–3 months. We collected data including author’s name, period of publication, sample size, mean age of patients, sex ratio, stone location, stone size, BMI, first SFR, final SFR, OT, number of surgeries, LOS, hemoglobin drop, total complications, Clavien grade I and II complications. Complications included: fever, bleeding, pyelion perforation, and urine leakage. Each article was identified using the first author’s name along with the year of publication. In the event of any disagreement during data extraction, resolutions were obtained through discussions or intervention from a third-party researcher if needed.

Quality assessment

The literature included was selected based on the scoring criteria from the Newcastle-Ottawa Scale (NOS). This criterion takes into account the selection of study participants, the comparability between different groups, and the measurement of exposure factors. Each factor was evaluated and assigned a score of either 1 point for appropriateness or 0 points for lack of description. Studies scoring between 0 and 5 were categorized as being of low quality, while those with scores ranging from 6 to 9 were considered high quality, following established reference criteria [23] (Table 2). It was used to assess the quality of the survey methodology. The full text of the included literature was read and independently assessed by two researchers. If the assessments of the two researchers were inconsistent, a third person performed the reassessment.

Statistical analysis

We carried out a meta-analysis by employing the Cochrane Collaboration’s RevMan 5.4 software. For dichotomous variables, we applied the Odds Ratio (OR) as the unified statistical metric. For continuous variables, we used the Mean Difference (MD) as the unified statistic. We regarded the effect sizes in terms of 95% confidence intervals (CI). P-values and I2 for OR and MD were used to evaluate the heterogeneity of the included literature, with P < 0.05 considered statistically different, and the I2 statistic was used to assess the heterogeneity of the studies. Fixed effects models were used if heterogeneity was less than 50%, otherwise, random effects models were used. If heterogeneity was present in the study, the source of heterogeneity was continuously analyzed until it was minimized.

Subgroup analysis

We performed subgroup analyses of overall complication, First SFR, Final SFR, OT, LOS, Grade I complications, Grade II complications according to overweight and obese populations. We also performed subgroup analyses of overall complication, First SFR, Final SFR, OT, LOS, Grade I complications, Grade II complications according to those with stones ≤ 2 cm and those with stones > 2 cm, the size of the sheath used for MiniPCNL, body position, and age.

Results

Study selection and characteristics

The initial search of the literature collected a total of 85 studies, of which we manually retrieved an additional 8 studies, totaling 93 original papers. No duplicates were found when performing duplicate literature screening, and after eliminating 77 irrelevant studies, we further evaluated the remaining 16. Finally, 9 literature were included in our meta-analysis [12,13,14,15,16,17,18,19, 24]. The process and outcomes of the literature review are illustrated in Fig. 1 (Fig. 1). The principal attributes of the studies incorporated in our research are delineated in Table 1.

Fig. 1
figure 1

Eligible study screening flowchart

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Table 1 Basic characteristics of the included studies
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Table 2 Evaluations of the selected research literature based on the Newcastle-Ottawa Quality Assessment Scale for retrospective case-control studies
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Overall complications and subgroup analysis

All studies provided information on complications. Because of large heterogeneity (P < 0.00001, I2 = 80%). was observed, the random-effects model was used. The complication rate was 19.1% (99/517) in the miniPCNL group and 10.9% (66/605) in the RIRS group. The two groups had no significant difference (OR = 1.51, 95% CI [0.60, 3.81], P = 0.39; Fig. 2A).

Fig. 2
figure 2

Forest plot for overall complications

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So, we performed subgroup analyses. For 4 studies in obese patients, the overall complication rate was higher in the miniPCNL group than in the RIRS group (31.71% vs. 9.86%). There was a statistically significant difference in the overall rate of complications between the miniPCNL group and the RIRS group. (OR = 5.09, 95% CI [2.58, 10.07], P < 0.00001; Fig. 2A).

Subgroup analysis was carried out according to stone size, with a compilation of 8 studies indicating overall complications. The pooled result showed that the overall complication rate was similar in both groups (random-effects model: OR = 1.56, 95% CI [0.55, 4.40], P = 0.40; Fig. 2B). Within the 3 studies focusing on stones larger than 2 cm, the overall complication rate was notably higher in the MiniPCNL group compared to the RIRS group (32.1% vs. 10.7%), establishing a statistically significant difference between the two groups. (OR = 4.68, 95% CI [2.02, 10.82], P < 0.0003; Fig. 2B).

Subgroup analyses of body position and age showed no statistical differences between the two groups (random effects mode: OR = 1.51, 95% CI [0.60, 3.81], P = 0.39). In terms of sheath size, showed that there was no statistically significant difference between the two groups in sheaths ≤ 14 (random-effects model: OR = 0.68, 95% CI [0.02, 23.25], P = 0.83) and that performing MiniPCNL in sheaths > 14 F had a higher overall complication rate. (OR = 2.88, 95% CI [1.42, 5.85], P = 0.003).

Grade I complications and subgroup analysis

7 studies were pooled to assess grade I complications between two groups. We used the fixed-effects mode (P = 0.18, I2 = 33%). Pooled data indicated significantly higher grade I complications in the MiniPCNL group than RIRS group (OR = 2.43, 95% CI [1.54, 3.82], P = 0.0001; Fig. 3A) in the obese or overweight patient population.

Fig. 3
figure 3

Forest plot for Grade I complications

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Subgroup analyses revealed that there was a total of 3 studies for overweight patients, and there was no statistically significant difference between the two groups for MiniPCNL and RIRS (OR = 0.69, 95% CI [0.21, 2.23], P = 0.54; Fig. 3A). Conversely, among the 4 studies focusing on obese patients, there were statistically higher instances of grade I complications associated with MiniPCNL as compared to RIRS (OR = 3.11, 95% CI [1.87, 5.17], P < 0.0001; Fig. 3A).

In a subgroup analysis of stone size, 6 studies reported grade I complications, Pooled data indicated grade I complications were higher in MiniPCNL than in RIRS (fixed-effects model: OR = 2.73, 95% CI [1.69, 4.42], P < 0.0001; Fig. 3B). Conversely, in the 3 studies with stones > 2 cm, there was a statistically significant difference with the MiniPCNL group exhibiting a higher rate of grade I complications than the RIRS group (OR = 2.96, 95% CI [1.73, 5.06], P < 0.0001; Fig. 3B).

In terms of sheath size, which showed a statistically significant difference between the two groups in both ≤ 14 F and > 14 F sheaths as performing MiniPCNL had more grade I complication rates (fixed model OR = 2.62, 95% CI [1.64, 4.18], P < 0.0001). In terms of age, we performed subgroup analyses, which showed that grade I complications were higher with MiniPCNL than with RIRS in ≤ 50 years of age (fixed-effects model and OR = 3.42, 95% CI [1.74, 6.74], P = 0.0004), whereas there was no statistically significant difference between the two groups in > 50 years of age (OR = 1.80, 95% CI [0.96, 3.35], P = 0.07).

Grade II complications and subgroup analysis

6 studies were pooled to assess grade II complications between two groups. The variance between the two groups was not statistically significant (random-effects model: OR = 1.80, 95% CI [0.58, 5.59], P = 0.31; Fig. 4A).

Fig. 4
figure 4

Forest plot for Grade II complications

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During a subgroup analysis focusing on stone size, 6 studies detailed grade II complications. The disparity between the two groups did not attain statistical significance, (random-effects model: OR = 1.84, 95% CI [0.47, 7.24], P = 0.38; Fig. 4B). Likewise, in 2 studies that scrutinized stones of ≤ 2 cm in size, no statistically significant discrepancy was detected between the groups (OR = 0.74, 95% CI [0.02, 22.14], P = 0.86; Fig. 4B). The 3 studies that considered stones of > 2 cm, in studies with stones > 2 cm, grade II complications were higher in MiniPCNL (OR = 2.95, 95% CI [0.62, 14.12], P = 0.18; Fig. 4B).

In terms of sheath size, Grade II complications were higher in the MiniPCNL group using ≤ 14 F sheaths than in the RIRS group, with a statistically significant difference between the two groups (OR = 6.60, 95% CI [2.17, 20.04], P = 0.0009).

Hemoglobin drop

Hemoglobin drop was noted across 4 studies that displayed significant heterogeneity (P < 0.00001, I2 = 96%), which was evaluated using a random-effects model. There was no statistically significant discrepancy discerned between the two groups (MD = 0.38, 95% CI [-0.04, 0.81], P = 0.08; Fig. 5A).

Fig. 5
figure 5

Forest plot for first SFR

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For obese and overweight patients, there were no statistical differences between the two groups in terms of sheath size. (random-effects model: MD = 0.38, 95% CI [-0.04, 0.81], P = 0.08; MD = 0.30, 95% CI [-0.18, 0.79], P = 0.22;). In terms of age, we performed subgroup analyses, which were analyzed using a random-effects model (P < 0.00001, I2 = 96%) and showed that hemoglobin drop was higher with MiniPCNL than with RIRS in > 50 years of age (MD = 1.27, 95% CI [0.90, 1.64], P < 0.00001), whereas there was no statistically significant difference between the two groups in ≤ 50 years of age (MD = 0.11, 95% CI [-0.21, 0.44], P = 0.50). Our subgroup analysis of position during MiniPCNL, using a random-effects model (P < 0.00001, I2 = 96%), showed that hemoglobin decreased more in the supine position, which was statistically different between the two groups (MD = 1.27, 95% CI [0.90, 1.64], P < 0.00001).

First stone-free rate and subgroup analysis

First SFR was reported in 7 included studies. with heterogeneity across studies (P = 0.02, I2 = 59%), and were analyzed using a random-effects model. In total, the first SFR could be calculated to be 86.2% (380 of 441 patients) in MiniPCNL and 70.1% (372 of 531 patients) in RIRS. There was a statistical difference between the two groups (OR = 2.22, 95% CI [1.25, 3.96], P = 0.007; Fig. 6A).

Fig. 6
figure 6

Forest plot for first SFR

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The findings from the subgroup analyses are elucidated as follows: For a total of 3 studies in obese patients, the first SFR could be calculated to be 84.3% (177 of 210patients) in MiniPCNL and 61.4% (189 of 308patients) in RIRS. There was a significant difference between the two groups (OR = 3.04, 95% CI [1.61, 5.75], P = 0.0006; Fig. 6A).

Subgroup analyses of stone size were performed, 6 included studies that reported the first SFR. The first SFR was 87.7% (336 of 383 patients) for MiniPCNL and 69.0% (325 of 471 patients) for RIRS. A statistically significant disparity was observed between the two groups (fixed-effects model: OR = 2.92, 95% CI [2.01, 4.24], P < 0.00001; Fig. 6B). For a total of 4 studies with stones ≤ 2 cm, the first SFR was 87.9% (204 of 229patients) for MiniPCNL and 82.1% (177 of 219patients) for RIRS, and MiniPCNL was associated with a higher first SFR (OR = 1.99, 95% CI [1.16, 3.44], P < 0.01; Fig. 6B). There was the same conclusion reached in 2 studies with stones > 2 cm studies (OR = 4.02, 95% CI [2.39, 6.77], P < 0.00001; Fig. 6B).

In terms of sheath size, we used a random-effects model (P = 0.005, I2 = 73%) for assessment, and there was no statistical difference between the two groups (OR = 1.85, 95% CI [0.92, 3.74], P = 0.09). In terms of age, we performed subgroup analyses, which were analyzed using a random-effects model (P = 0.02, I2 = 59%) and showed that MiniPCNL performed in ≤ 50 years of age had a higher FIRST SFR, which was statistically different between the two groups (OR = 3.96, 95% CI [2.18, 7.16], P < 0.00001).

Final stone-free rate and subgroup analysis

Final SFR was reported in 7 included studies. The final SFR could be calculated to be 90.0% (377 of 419 patients) in the MiniPCNL group and 84.7% (437 of 516 patients) in the RIRS group. There was a statistical difference between the two groups (fixed-effects model: OR = 1.75, 95% CI [1.16, 2.63], P = 0.007; Fig. 7A).

Fig. 7
figure 7

Forest plot for final SFR

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The results of the subgroup analyses are presented below: For a total of 3 studies in overweight patients. The pooled result showed that there was no statistical difference between the two groups (OR = 1.18, 95% CI [0.52,2.65], P = 0.70; Fig. 7A). For a total of 4 studies in obese patients, the final SFR was 88.8% (238 of 268patients) in MiniPCNL group and 82.2% (300 of 365patients) in RIRS group. There was a notable disparity between the two groups (OR = 1.99, 95% CI [1.24,3.21], P = 0.005; Fig. 7A).

Subgroup analyses of stone size were performed, and 6 studies reported a final SFR. The final SFR was 90.9% (328 of 361 patients) for MiniPCNL and 84.2% (384 of 456 patients) for RIRS. A notable statistical discrepancy was observed between the two groups (fixed-effects model: OR = 2.05, 95% CI [1.30, 3.22], P = 0.002; Fig. 7B). In the 3 studies with stones > 2 cm, the final SFR was 91.0% (193 of 212patients) for MiniPCNL and 83.2% (257 of 309patients) for RIRS, indicating a higher final for MiniPCNL (OR = 2.38, 95% CI [1.34, 4.20], P = 0.003; Fig. 7B).

We performed a subgroup analysis of the intraoperative position in MiniPCNL using a fixed-effects model (P = 0.25, I2 = 23%) with higher final SFR in the prone position, which was statistically different between the two groups (OR = 1.78, 95% CI [1.17, 2.71], P = 0.007). In terms of age, we performed subgroup analyses showed that MiniPCNL performed in ≤ 50 years of age had a higher final SFR (fixed-effects model: OR = 3.46, 95% CI [1.70, 7.06], P = 0.0006). In terms of sheath size, we used a fixed-effects model (P = 0.25, I2 = 23%) for subgroup analysis, and we found that the final SFR was higher with sheaths > 14 F (OR = 1.61, 95% CI [1.02, 2.53], P = 0.04).

Operative time and subgroup analysis

Data relevant to OT was procured from nine distinctive studies. The discrepancy between the two groups was not statistically significant (random-effects model: MD = 7.97, 95% CI [-6.91,22.86], P = 0.29; Fig. 8A).

Fig. 8
figure 8

Forest plot for OT

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Subgroup analysis showed no statistically significant differences between the two groups in both obese and overweight patients (MD = 15.76, 95% CI [-11.08,42.61], P = 0.25; MD=-1.80, 95% CI [-14.59,11.00], P = 0.78; Fig. 8A).

During the subgroup analysis concerning stone size, 8 studies provided information on the duration of surgery. The pooled result showed that there was no statistical difference between the two groups (MD = 2.82, 95% CI [-10.76,16.41], P = 0.68; Fig. 8B).

We performed a subgroup analysis of intraoperative MiniPCNL positions using a random-effects model (P<0.00001, I2 = 97%) with longer OT in the supine position (MD = 7.97, 95% CI [-6.91, 22.86], P = 0.29). In terms of age, we performed subgroup analyses, which were analyzed using a random-effects model(P<0.00001, I2 = 97%) and showed that MiniPCNL performed in ≤ 50 years of age had a shorter OT(MD=-10.60, 95% CI [-20.02, -1.17], P = 0.03), and the same was true in > 50 years of age, and was statistically significant between both groups(MD = 23.08, 95% CI [2.37, 43.80], P = 0.03).In terms of sheath size, OT was similar between the two groups (random effects model: MD = 9.58, 95% CI [-8.24, 27.41], P = 0.29).

Length of hospital stay and subgroup analysis

Data on LOS could be obtained in 9 studies, Meta-analysis showed no statistical significance between the two groups (random-effects model: MD = 1.03, 95% CI [-0.07, 2.14], P = 0.07; Fig. 9A).

Fig. 9
figure 9

A: Forest plot for hemoglobin drop; B: Forest plot for number of surgeries.

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The results of the subgroup analyses are presented below: There was a total of 4 studies in obese patients and the difference between the two groups was statistically significant (MD = 1.84, 95% CI [0.68, 3.01], P = 0.002; Fig. 9A).

In a subgroup analysis of stone size, in each of the 3 studies evaluating stones > 2 cm, there was a statistically notable difference between the two groups, with MiniPCNL contributing to an extended LOS (MD = 2.01, 95% CI [0.53,3.50], P = 0.008; Fig. 9B).

We performed a subgroup analysis of intraoperative MiniPCNL positions using a random-effects model(P<0.00001, I2 = 98%) with no statistical difference between the two groups(MD = 1.03, 95% CI [-0.07, 2.14], P = 0.07). In terms of age, Meta-analysis demonstrated that there was a longer LOS for MiniPCNL performed in > 50 years of age, (random-effects model MD = 1.39, 95% CI [0.26, 2.53], P = 0.02). In terms of sheath size, we used a random-effects model(P<0.00001, I2 = 99%) for subgroup analysis, and the use of > 14 F sheaths at the time of performing MiniPCNL had a longer LOS (MD = 1.76, 95% CI [0.62, 2.90], P = 0.02).

Number of surgeries

An aggregate of 2 studies reported the number of surgical procedures. These showed a consistent homogeneity across the studies (P = 0.79, I2 = 0%), and were subjected to analysis utilizing a fixed-effects model. In patients who are obese or overweight, MiniPCNL necessitated fewer secondary procedures relative to RIRS (MD=-0.19, 95% CI [-0.26, -0.12], P < 0.00001; Fig. 5B).

We performed a subgroup analysis of intraoperative positions for MiniPCNL, which showed that more procedures needed to be performed when the supine position was used(random-effects model: MD = 1.27, 95% CI [0.90, 1.64], P<0.00001).

Publication bias analysis

In conducting a funnel plot analysis, the incidence of postoperative Grade I complications was utilized. Every piece of relevant literature assessed fell within the 95% CI. The distribution was predominantly symmetrical, suggesting the absence of a noteworthy publication bias (Fig. 10). Comprehensive sensitivity analyses were performed on all studies by sequentially eliminating them to assess each one’s impact on the collective outcomes. Despite the exclusion of specific studies, there were no alterations in the cumulative results.

Fig. 10
figure 10

Funnel plot

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Discussion

For patients who are overweight or obese and dealing with kidney stones, RIRS and MiniPCNL are predominantly employed for their treatment. As laid out by the guidelines, PCNL is typically suggested for renal stones larger than 2 cm. RIRS is an alternative, however, PCNL’s advantages include a higher SFR and decreased OT. Its disadvantages, though, include a greater postoperative complication rate and an elevated risk of bleeding. For significant stones larger than 2 cm, there exists little doubt that PCNL is the optimal choice [25]. However, according to a recent study by Prof. Tolga, in patients with 2–4 cm kidney stones, a similar final SFR to PCNL can be achieved with multistage RIRS, which is also safer [8]. With advances in surgical techniques, a new surgical procedure, MiniPCNL, has emerged as an effective alternative treatment to PCNL [26]. A meta-analysis by Chuanping Wan et al. comparing MiniPCNL with standard PCNL showed that the safety and efficacy of Mini-PCNL in the treatment of renal stones was comparable to that of standard PCNL, with a similar SFR. Additionally, compared to standard PCNL, MiniPCNL has several advantages such as reduced LOS, minimized hemoglobin drop, fewer required blood transfusions, heightened postoperative tubelessness, and a decrease in complications. However, it is important to note that the duration of the operation tends to be prolonged with MiniPCNL [10]. Some patients cannot tolerate renal impairment, surgical trauma, and perioperative complications associated with standard percutaneous nephrolithotomy. MiniPCNL has received widespread attention as a potential treatment option.

The merits and drawbacks of MiniPCNL versus RIRS in surgically treating kidney stones among overweight or obese patients remain ambiguous. A substantial portion of prior studies has primarily centered on juxtaposing the safety and efficacy of MiniPCNL and RIRS for kidney stone treatment in both normal-weight and obese individuals. Motivated by these uncertainties, we carried out a meta-analysis to investigate and juxtapose the safety and efficacy of the two surgical approaches, MiniPCNL and RIRS, in addressing kidney stones for patients who are overweight or obese.

Potential complications constitute a critical aspect while assessing the safety of both procedures and serve as a key consideration for the operator. Typical complications associated with both surgical methods can include bleeding, perforation, fever, and urinary leakage [10]. However, most obese or overweight patients, may suffer from metabolic syndrome (MetS), and some may suffer from chronic kidney disease (CKD), which are generally infected stones with a high chance of infection/sepsis if RIRS is performed, Patients with CKD have poorer renal function, produce less urine, and have lower clearance after RIRS, leading to increased intrarenal pressure or hydronephrosis, which in turn leads to prolonged LOS, especially in those with stone size > 2 cm. Univariate analysis in a single-center retrospective study by Junxiu Hao et al. found that patients with MetS had a higher risk of infection and were more likely to develop urinary sepsis. Similarly, in a multicenter prospective study by Francesco Berardinelli et al., patients with CKD were found to be positively associated with infectious complications after RIRS [27, 28].

In terms of overall complications, our study showed that for both procedures, MiniPCNL had a significantly higher overall complication rate than RIRS (19.1% vs. 10.9%,). However, there was no statistical discrepancy of significance discerned between the MiniPCNL and RIRS groups. Subgroup analyses showed a statistically significant difference in the overall complication rates for both procedures in obese patients and in patients with stones > 2 cm, the probability of overall complications was greater in obese patients and in patients with larger stone loads, which is in line with the results shown in most studies [29, 30]. However, in a study conducted by Faruk Ozgor (2018) et al. on kidney stones in older adults greater than 60 years of age, it was suggested that there was no statistically significant difference between MiniPCNL and RIRS in terms of complications, and we analyzed that it might be due to the lack of maturity as well as the imperfect equipment of MiniPCNL and RIRS at that time, in addition to the size and position of the stone as its influencing factors [17]. Therefore, we performed another subgroup analysis and showed that for Grade I complications, the results showed consistency concerning overall complications. However, there was no discernible statistical significance in the occurrence of Grade II complications between the two groups, which may be due to the rarity of serious complications arising from the two surgical modalities and may also be related to the fact that we included fewer studies. However, in our subgroup analysis of sheath size for MiniPCNL, we found that postoperative Grade II complications occurred more frequently with sheaths ≤ 14 F. We consider that this may be related to the fact that sheaths < 14 F cause high pressure in the renal pelvis, which can lead to postoperative infections, and according to a study by Marco Nizzardo et al. comparing the use of negative pressure suction sheaths to the use of no sheaths, the use of negative pressure suction sheaths can reduce the internal pelvic pressure and at the same time reduce the risk of infections [31].

As one of the indicators to measure the effectiveness of stone treatment methods, SFR has been a major concern for clinicians. Meta-analysis showed that the MiniPCNL group was higher than the RIRS group in terms of first SFR and the results were statistically significantly different, which is consistent with the results of previous studies. Subgroup analysis showed a statistically significant difference between MiniPCNL and RIRS in terms of first SFR in obese patients. Subgroup analysis showed a statistically significant difference between MiniPCNL and RIRS in terms of first SFR in obese patients and patients with stones > 2 cm, but in terms of final SFR, only obese patients showed a statistically significant difference between MiniPCNL and RIRS, and subgroup analysis in terms of stone size showed that either for patients with kidney stones ≤ 2 cm or > 2 cm, the MiniPCNL had a higher SFR. However, in the study by Faruk (2016) et al., both the first SFR and the final SFR were higher for MiniPCNL than for RIRS, with no statistical significance between the two (p = 0.371), and after reviewing the literature, we found that this may be related to the fact that they included fewer patients in their study [14].

However, a new type of ureteral flexible sheath, FANS, has emerged that offers greater flexibility, higher SFR, a more pronounced completely stone-free state, a shorter LOS, and a lower complication rate compared to previous ureteral flexible sheaths. This is also illustrated by a recent single-center retrospective study comparing MiniPCNL and RIRS with FANS for 2–3 cm renal stones [32, 33]. According to Yujun Chen et al. FANS allow the sheath to be sheathed over the stone and connected to a negative-pressure suction device, which allows the stone to be broken up inside the sheath, thus reducing the corresponding complications, and also reduces the need for a mesh basket to be sheathed, and can achieve the same level of flexibility as MiniPCNL, with a lower LOS. And an SFR similar to that of the MiniPCNL can be achieved [34].

In terms of operative time (OT), our study showed no statistically significant difference between MiniPCNL and RIRS. However, in the study by Chen et al., the OT of MiniPCNL was significantly less than that of RIRS [18]. After reading the literature, we found that there were two main reasons for this result, one was because negative pressure suction was used to aspirate stone fragments during MiniPCNL, and the other was because ureteral stents were not placed in 14 patients postoperatively.

Our meta-analysis revealed no statistically significant disparity between the two surgical methods in terms of LOS. However, in the subgroup analysis, the LOS for MiniPCNL was greater than that for RIRS in obese patients and patients with stones larger than 2 cm, and there existed a statistically significant discrepancy between the two procedures. Firstly, subgroup analysis for stones > 2 cm showed that more OT was required in the removal of larger stones, and secondly, it took more time to perform MiniPCNL in obese or overweight people, probably because of the prolonged skin-to-stone distance of the puncture needle through the skin and fat to reach the kidney, and the restriction of sheath and nephrolithoscope movement due to excess adipose tissue as well as the inability to access the calyces adequately, thus leading to a greater risk of bleeding, infection, and longer postoperative recovery time, and therefore a prolonged LOS [35]. We found that in the three included studies with stones > 2 cm, the MiniPCNL group had a higher probability of complications such as intraoperative bleeding, a higher rate of postoperative hemoglobin drop, and then a higher probability of postoperative transfusion as well as prolonged bed rest [16, 18, 24].

Faruk (2018) et al., Armagan et al., and Cepeda et al. showed that MiniPCNL had a higher rate of hemoglobin reduction than RIRS in both procedures [12, 15, 17]. Another study showed that RIRS had a higher rate of hemoglobin decline than MiniPCNL [19]. Our meta-analysis revealed that the disparities in the postoperative hemoglobin drop and the OT did not display a statistically significant difference between the two groups. This could potentially be attributed to the inclusion of a few lower-quality studies and the limited quantity of certain examined literature. Therefore, to obtain more accurate results, more high-quality clinical articles are needed to provide proof of evidence.

We did not compare the economic costs between the two surgical modalities because only a few of the included literature raised issues related to hospitalization costs, and performing multiple surgical procedures in a single hospitalization may add more economic burden and longer LOS. Especially in the case of stones > 2 cm, it is difficult to avoid the need for multiple RIRS procedures and the need for multiple anesthesia, which in turn imposes a significant economic burden on the patient and a correspondingly longer LOS. According to a study by Martin Schoenthaler, the overall average cost of Ultra-MiniPCNL was 656 euros, whereas the overall average cost of RIRS was 1,160 euros, and the total postoperative cost of RIRS was nearly twice as high as the total postoperative cost of Ultra-MiniPCNL. twice the total cost. However, for RIRS less intraoperative injury was favored by more patients.

From the literature included in the meta-analysis, there was some heterogeneity in this study, which may be analyzed for the following reasons: (1) overall complications, first SFR and length of hospitalization may be highly related to the surgical experience of the operator, the location of the stone, the use of surgical instruments and the laser power used for lithotripsy, which inevitably caused bias; (2) the underlying conditions of different patients and the treatment protocols that they underwent in the postoperative period varied, which had an impact on the length of hospitalization; (3) The definitions of SFR, FirstSFR, and FinalSFR were not identical for the included articles, and therefore, some selection bias may have resulted. This study admittedly comes with certain limitations. Among the 9 papers incorporated in our research, only 2 were prospective studies while the remaining 7 were retrospective. Due to the different levels of bias and quality of the included literature, more high-quality, well-designed, randomized, controlled, multicenter trials are needed to demonstrate the advantages and disadvantages of MiniPCNL and RIRS in the population of obese or overweight patients with kidney stones. The absence of high-quality randomized controlled trials (RCT) may have somewhat compromised the reliability of our results. This could potentially be linked to the increased incidence of complications stemming from MiniPCNL, as well as the extended recovery period required by patients following the procedure.

However, for our inclusion, the article did not specify which of the line RIRS groups were primary RIRS or pre-stent-tube RIRS, because the SFR was higher in the pre-stent-tube RIRS group. This would have confounded our findings.

Conclusion

Our analysis showed safety and efficacy of MiniPCNL for the treatment of kidney stones in overweight patients is comparable to that of RIRS. In addition, in obese patients, MiniPCNL had more overall postoperative complications, higher first SFR, higher final SFR, and fewer surgeries with RIRS. Whereas in patients with stones>2 cm MiniPCNL had more overall postoperative complications, higher final SFR, and LOS. The use of larger sheaths, the older the patient, may result in more complications, prolonged OT, prolonged LOS, and increased hemoglobin drop.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Abbreviations

PCNL:

Percutaneous nephrolithotomy

MiniPCNL:

Mini percutaneous nephrolithotomy

RIRS:

Retrograde intrarenal surgery

SFR:

Stone-free rate

LOS:

Length of hospital stay

OT:

Operative time

CNKI:

Chinese National Knowledge Infrastructure

NOS:

Newcastle‒Ottawa Scale

OR:

Odds Ratio

WMD:

Weighted mean difference

CI:

95% Confidence intervals

NA:

Not available

FANS:

Flexible And Navigable Suction

f-URS:

Flexible ureteroscopes

UAS:

Ureteral access sheath

SM:

Supplementary material

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Acknowledgements

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Funding

No project funding was received for this study.

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Author notes

  1. Ming Qiu, Hongjin Shi and Fabin Yang contributed equally to this work.

Authors and Affiliations

  1. Department of Urology, The Second Affiliated Hospital of Kunming Medical University, Situated at 374 Dianmian Avenue, Wuhua District, Kunming, 650101, China

    Ming Qiu, Hongjin Shi, Pingchu Li, Shi Fu, Jiansong Wang, Haifeng Wang, Yigang Zuo & Jinsong Zhang

  2. Yunnan Maternal and Child Health Hospital, Situated at 200 Gulou Road, Wuhua District, Kunming, 650051, China

    Fabin Yang

  3. Department of Urology, Menghai County People’s Hospital, Situated at 11 Xiangshan Road, Menghai Town, Menghai County, Xishuangbanna Dai Autonomous Prefecture, Yunnan, 666100, China

    Qiao Yang

  4. Department of Respiratory Medicine, The Second Affiliated Hospital of Kunming Medical University, situated at 374 Dianmian Avenue, Wuhua District, Kunming, 650101, China

    Bing Hai

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Contributions

ZJS and WJS: design of the study concept and trial protocol, QM, SHJ, LPC and FS: literature screening, QM, SHJ and WHF: quality assessment of the included studies, QM, SHJ, YQ and YFB: data analysis and interpretation of the data, QM and HB: drafting of the manuscript, ZYG and ZJS: supervision.

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Correspondence to Bing Hai or Jinsong Zhang.

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Qiu, M., Shi, H., Yang, F. et al. Comparison of the efficacy and safety of mini-percutaneous nephrolithotomy versus retrograde intrarenal surgery for the treatment of kidney stones in overweight or obese patients: a systematic review and meta-analysis. BMC Urol 24, 243 (2024). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12894-024-01588-4

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BMC Urology

ISSN: 1471-2490

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