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Review

Free Access

Comparison of Holmium: YAG Laser and Pneumatic Lithotripsy in the Treatment of Ureteral Stones: An Update Meta-Analysis

Chen S. · Zhou L. · Wei T. · Luo D. · Jin T. · Li H. · Wang K.

Author affiliations

Department of Urology, Institute of Urology, West China Hospital, Sichuan University, Chengdu, PR China

Corresponding Author

Kunjie Wang

Department of Urology

Institute of Urology, West China Hospital, Sichuan University

Guo Xue Xiang 37, Chengdu, Sichuan 610041 (China)

E-Mail wangkj@scu.edu.cn

Related Articles for ""

Urol Int 2017;98:125-133

Abstract

Purpose: Holmium YAG laser lithotripsy (LL) and pneumatic lithotripsy (PL) are the most commonly used procedures in the treatment of ureteral calculi. In a previous meta-analysis examining the treatment effect of the 2 modalities, the authors highlighted the need for large sample size and high quality trials to provide more uncovered outcome. Recently, several randomized controlled trials (RCTs) evaluating the same issue with larger patient number and more complicated data have been published. Therefore, we conducted this meta-analysis to update and synthesize evidence on the efficacy and safety of the 2 procedures in the treatment of ureteral calculi. Methods: The relevant studies were identified by searching Medline, EMBASE and Cochrane Library Database from January 1990 to November 2015. RCTs assessing the efficacy and safety of Holmium YAG laser and PL for ureteral stones were included. Two reviewers independently screened studies and extracted data. Results: A total of 8 studies were identified including 1,555 patients. Compared with PL, Holmium YAG LL significantly reduced the mean operative time (weighted mean difference = -11.52, 95% CI -17.06 to -5.99, p < 0.0001) and increased the early stone-free rate (OR 2.69, 95% CI 1.91-3.78, p < 0.00001) and the delayed stone-free rate (OR 2.12, 95% CI 1.40-3.21, p = 0.0004). However, a higher postoperative ureteral stricture rate (OR 3.38, 95% CI 1.56-7.31, p = 0.002) was observed in LL group over PL group. There was no statistical significance in the ureteral perforation rate (OR 1.19, 95% CI 0.65-2.16, p = 0.58), the stone migration rate (OR 0.64, 95% CI 0.41-1.00, p = 0.05), the postoperative gross hematuria rate (OR 0.71, 95% CI 0.40-1.25, p = 0.23) and the postoperative fever rate (OR 0.73, 95% CI 0.50-1.09, p = 0.12). Conclusions: Our data reconfirmed that Holmium LL for ureteral stones can achieve shorter mean operative time, better early and delayed stone-free rate with larger sample size and more high quality studies. And further trials are unlikely to considerably alter this conclusion. In terms of higher risk of postoperative ureteral stricture in LL group over PL group observed in our review, more high quality, multicenter RCTs with long-term follow-up outcome are warranted to better assess this issue.

© 2016 S. Karger AG, Basel


Introduction

Over the past decades, treatments for ureteral calculi evolve from open ureterolithotomy to minimally invasive procedures, including extracorporeal shock wave lithotripsy, ureteroscopic lithotripsy and laparoscopic lithotomy [1]. Among them, ureteroscopic lithotripsy holds the minimal contraindications, nearly available for all except severe ureteral stricture preventing successful scope passage [2]. Together with high stone-free rate and relatively low complications, ureteroscopic interventions become the main therapeutic way for large ureteral stones with indications in many academic centers.

In the process of ureteroscopic lithotripsy, electrohydraulic, ultrasonic, pneumatic and laser lithotripters are available. Amid them, Holmium YAG laser lithotripsy (LL) and pneumatic lithotripsy (PL) are the predominant procedures [3]. There is a trend in favor of using LL, owing to advantages on fragmentation and flexibility [4]. However, other authors thought that PL was comparable to LL in fragmentation efficiency, accompanying the advantage of low cost and easy installation [5]. Over the past decade, data comparing the efficacy and safety of LL and PL are inconclusive [5,6,7].

In 2013, a meta-analysis by Yin et al. [8], which included 4 trials and 295 patients, up to 2012, concluded that LL had a higher stone-free rate, a lower migration and retaining JJ catheter rate when compared with PL. It has been recommended that LL was a powerful, effective and safe technique for distal ureteral stones. Since 2012, there haves been 3 randomized controlled trials (RCTs) that were published with much more sample size and information on complications. And another RCT evaluating the same issue published in 2008 by Manohar et al. [7] was identified through systematic search. When comparing the efficacy and safety of LL and PL, a relatively small patient number and loss of useful data in many included studies weakened the validation of the results in the 2013 review by Yin et al. [8].

In the light of this, we conducted this updated meta-analysis in an effort to reveal a wealth of evidence and provide more valid information for clinical practice.

Methods

Literature Search and Study Selection

We searched the databases Medline, EMBASE and the Cochrane Library from January 1, 1990, to November 2015. The key words of search strategy are composed of ‘ureteral calculi', ‘laser lithotripsy', ‘pneumatic lithotripsy' (and multiple synonyms for each term). Relevant trials in the reference lists were also searched. The potentially eligible studies were screened by 2 authors (S.C. and L.Z.) independently.

Inclusion Criteria and Exclusion Criteria

Inclusion criteria were as follows: (1) RCT design of patients with ureteral stones; (2) studies comparing treatment of LL and PL for ureteral calculi; (3) English language; (4) only studies on humans; and (5) eligible trials that measured at least one of the following outcomes: mean operative time, early stone-free rate, delayed stone-free rate, stone migration rate, ureteral perforation, postoperative gross hematuria, postoperative fever and postoperative ureteral stricture.

Exclusion criteria are as follows: (1) patients of children; (2) comparative studies or cases series; and (3) patients with renal insufficiency, abnormal anatomy, associated renal stones, active kidney infection and active bleeding disorders.

Controversial trials were settled by consensus.

Data Extraction and Outcomes of Interest

Primary information, including mean ± SDs, OR and 95% CI, was extracted directly from articles by 2 investigators independently. Additional data were extracted from the studies, including the first author, year of publication, sample size and other clinical characteristics.

The main concerned outcomes included mean operative time, stone migration rate, early stone-free rate (assessment within 1 month postoperation), delayed stone-free rate (assessment from 1 to 3 months postoperation), ureteral perforation rate, postoperative gross hematuria rate, postoperative fever and postoperative ureteral stricture rate.

Study Quality and Level of Evidence

The quality of these eligible citations was assessed using the Cochrane handbook, which was independently graded by 2 reviewers (S.C. and L.Z.). Quality assessment checklist consisted of the following items: the details of randomization, allocation concealment, blinding of investigators, participants, outcome assessors, intention to treat analysis, selective outcome report, completeness of follow-up and comparable basic characteristics. On the basis of above items, studies were divided into 3 categories as follows: (1) all quality components adequate - low risk of bias; (2) one or more of the quality components unclear - moderate risk of bias; and (3) one or more of the quality components inadequate - high risk of bias.

Statistical Analysis

The Review Manager 5.3 software (The Cochrane Collaboration, Oxford, UK) statistical package was used to analyze the ORs for dichotomous variables and the mean differences for continuous variables as well as 95% CI. The proportion of heterogeneity across the studies was tested using the χ2 and the I2 index (range 0-100%). If significant heterogeneity was found (p < 0.1 and I2 = 50%), we performed subgroup analysis or sensitivity test. If the heterogeneity still existed, the random effects model was adopted. Otherwise, we used a fixed effects model with the Mantel-Haenszel method to calculate the pooled OR. All p values were two-tailed and p < 0.05 was considered statistically significant. Begg's test was used in a funnel plot of log OR against its SE to assess publication bias, and Egger's unweighted regression asymmetry test was used to detect the degree of asymmetry [9,10].

Results

Methodological Quality and Baseline Characteristics

Figure 1 shows the process of study selection. All included 8 studies were randomized controlled studies published in 2008-2015 [3,7,11,12,13,14,15,16] (table 2). According to Cochrane handbook, 1 study was graded as A and 7 studies were graded as B (table 1). The standard format should be comprised of the following sections: (1) general information about the study, including the authors, publication year, interval of time in which the subjects were enrolled, total number of patients, nationality of the study, gender and age (range and mean); (2) inclusion and exclusion criteria, stone location and stone diameter; (3) type of surgical procedure and stone fragmentation device, antibiotic prophylaxis and time of the surgical procedure; and (4) early stone-free rate, delayed stone-free rate, ureteral perforation rate, stone migration rate and number and type of other complications. Overall, the baseline characteristics of the 8 included trials were comparable. Totally, 1,555 objects were incorporated in this meta-analysis.

Table 1

Quality assessment of included studies

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Table 2

Characteristics of included studies

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Fig. 1

Flowchart of study selection for the meta-analysis.

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Outcomes

Mean Operative Time

All studies, aside from Maghsoudi et al. [16], unequivocally compared the mean operative time. We excluded studies by the Manohar et al. [7], Garg et al. [15] and Razzaghi et al. [3] because they only counted the lithotripsy time. High level of heterogeneity was detected among the studies (I2 = 76%). Without finding the sources of heterogeneity by a sensitivity analysis, we applied the random effects model. The result showed that there was a significant difference between the 2 groups, the mean operative time of LL was much shorter than that of PL group (weighted mean difference = -11.52, 95% CI -17.06 to -5.99, p < 0.0001; fig. 2).

Fig. 2

Comparison of LL vs. PL on the mean operative time.

http://www.karger.com/WebMaterial/ShowPic/515160

Early Stone-Free Rate

Except Cimino et al. [12], Maghsoudi et al. [16] and Manohar et al. [7] assessing stone-free rate later than 1 month post operation, all the other trials reported information on early stone-free rate. The results showed LL improved an early stone-free rate than PL (OR 2.69, 95% CI 1.91-3.78, p = 0.00001; fig. 3).

Fig. 3

Comparison of LL vs. PL on the early stone-free rate.

http://www.karger.com/WebMaterial/ShowPic/515159

Delayed Stone-Free Rate

Six studies included data about the delayed stone-free rate. With regard to this item, these mixed studies presented high homogeneity, as indicated by the figure 4. So, the fixed effects model was applied, showing that LL generated a higher delayed stone-free rate than PL (OR 2.12, 95% CI 1.40-3.21, p = 0.0004; fig. 4).

Fig. 4

Comparison of LL vs. PL on the delayed stone-free rate.

http://www.karger.com/WebMaterial/ShowPic/515158

Stone Migration Rate

Six trials conducted comparison on this item. Because of homogeneity across these studies (p = 0.22, I2 = 28%), the fixed effects model was carried out to integrate data. In terms of stone migration rate, no significance was detected among the 2 groups (OR 0.64, 95% CI 0.41-1.00, p = 0.05; fig. 5).

Fig. 5

Comparison of LL vs. PL on the stone migration rate.

http://www.karger.com/WebMaterial/ShowPic/515157

Ureteral Perforation Rate

All studies provided information on this item, 2 of which were not estimable on the OR. No obvious heterogeneity existed and we used the fixed effects model. The result suggested there was no significance between LL and PL in relation to ureteral perforation rate (OR 1.19, 95% CI 0.65-2.16, p = 0.58; fig. 6).

Fig. 6

Comparison of LL vs. PL on the ureteral perforation rate.

http://www.karger.com/WebMaterial/ShowPic/515156

Postoperative Gross Hematuria Rate

Five studies carried out the comparison on postoperative gross hematuria. Owing to heterogeneity (p = 0.08, I2 = 56%) of the included studies, we employed the random effects model. The result suggested that, with respect to this outcome, there was no significant difference between LL group and PL group (OR 1.08, 95% CI 0.4-2.94, p = 0.88; fig. 7).

Fig. 7

Comparison of LL vs. PL on the postoperative gross hematuria rate.

http://www.karger.com/WebMaterial/ShowPic/515155

Postoperative Ureteral Stricture Rate

Six trials presented information on postoperative ureteral stricture. A correspondingly high level of homogeneity was detected. LL resulted in more postoperative ureteral stricture than PL when tested for overall effect (OR 3.38, 95% CI 1.56-7.31, p = 0.002; fig. 8).

Fig. 8

Comparison of LL vs. PL on the postoperative ureteral stricture rate.

http://www.karger.com/WebMaterial/ShowPic/515154

Postoperative Fever Rate

Three studies showed data on postoperative fever rate. High homogeneity existed, and we adopted the fixed effects model. As a result, there were no significant difference between LL and PL group in this item (OR 0.73, 95% CI 0.5-1.09, p = 0.12; fig. 9).

Fig. 9

Comparison of LL vs. PL on the postoperative fever rate.

http://www.karger.com/WebMaterial/ShowPic/515153

Discussion

Summary of Main Findings

The aim of this systematic review was to integrate the current evidence for evaluating the effect of LL and PL in the treatment of ureteral calculi. The overall results of this meta-analysis indicate a trend favoring LL as the first choice for ureteral stones as is recommended by the European Association of Urology, that Holmium YAG laser is the most effective lithotripsy system, which has become the gold standard for ureteroscopy and flexible nephroscopy [17]. When compared with PL, shorter mean operative time, higher early and delayed stone-free rate were found in the LL group, without significant difference in terms of stone migration rate, ureteral perforation rate, postoperative gross hematuria rate and postoperative fever rate. Any reduction in favor of LL was postoperative ureteral stricture rate. However, this result was mainly driven by the study by Li et al. [11,] which reported much more postoperative ureteral stricture patients (n = 29) than the other studies (n = 5). However, postoperative ureteral stricture could be due to factors associated with surgical technique, rate of impaction and chronicity of stone presence that were not explicitly reported in their trial. Consequently, though with high homogeneity, caution should be exercised to interpret the result.

Limitations of Included Studies

This is a pooled study including 8 RCTs assessing the effect of 2 modalities for the treatment of ureteral calculi. High to moderate heterogeneity exited. I2 score for mean operative time rate, postoperative gross hematuria rate and early stone-free rate were 76, 56 and 47%, respectively. The high heterogeneity might be attributed to the following reasons: (1) included trials incorporated different segment ureteral stones - 5 studies [3,12,14,15,16] including proximal, middle, distal ureteral stones; 2 studies [11,13] including middle and distal ureteral stones; and 1 study [7] including upper ureteral stones only. As proximal ureteral stones are more difficult for ureteroscopic lithotripsy, mean operative time should be longer than that of middle and distal ureteral stones. Whilst data of mean operative time were not provided separately according to the stone position, subgroup analysis could not be made correspondingly. (2) Various pulse energy and frequencies were applied by different surgeons in the process of operation. Most trials employed 0.8-1.5 J energy in frequency of 5-15 Hz. Two studies [12,13] with a relatively low energy setting (0.5-1 J and 0.6-1.2 J) showed longer mean operation time. According to the research of Kronenberg and Traxer [18] and Wezel et al. [19], pulse energy was an essential variable affecting fragmentation efficiency. However, all studies presented a range of lithotripsy energy and frequencies, which were overlapped among each other, and made it impossible to exercise subgroup analysis. (3) A wide variation of familiarity with the 2 types of lithotripter between the operators might cause the high heterogeneity. Although some differences existed in the included studies, high homogeneity was generated in terms of delayed stone-free rate, ureteral perforation rate and postoperative fever rate to confirm the validation of these results.

Limitations of This Review

In order to minimize bias within this review, we performed an extensive literature search, and 2 reviewers independently screened the full texts for inclusion and extracted the data. However, without any attempt to source unpublished data from thesis and conference proceedings abstracts and articles in any other language than English, bias might be introduced. This method has also been questioned by some authors who claimed that truly unpublished studies frequently have poor methodology, and ones with better methodology often eventually become published [20]. So, it is impossible to know if it is truly a limitation or if there are unpublished studies considerable enough to alter our conclusions.

Comparison with the Previous Review

The aim of the meta-analysis by Yin et al. [8] was to compare the effect of the 2 techniques in the treatment of distal ureteral stones, but their study was composed of very small sample size and mixed proximal ureteral stones with distal ureteral stones. Our review further included more ureteral stone patients in different ureteral segments and elevated treatment target from distal to total ureter. Our main findings differ very little from the 2013 review; however, more robust conclusions about the effect of the 2 procedures can be drawn from our review. And a higher postoperative ureteral stricture rate was found in the LL group.

Conclusions

This study generally compared the efficacy and safety of LL and PL for the treatment of ureteral stones. Our review reconfirmed the result that, at the aspect of mean operative time, early and delayed stone-free rate, LL is superior to PL. And further studies are unlikely to considerably alter this conclusion. A higher risk of postoperative ureteral stricture for patients was also observed in our meta-analysis. However, more high quality, multicenter RCTs with long-term follow-up outcome are warranted to better assess this issue.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (grant Nos. 31370951 and 81470927), the National Science Foundation for Young Scholars of China (grant No. 81300579).

Disclosure Statement

No competing financial interests exist.


References

  1. Khaladkar S, Modi J, Bhansali M, Dobhada S, Patankar S: Which is the best option to treat large (>1.5 cm) midureteric calculi? J Laparoendosc Adv Surg Tech A 2009;19:501-504.
  2. Wright AE, Rukin NJ, Somani BK: Ureteroscopy and stones: current status and future expectations. World J Nephrol 2014;3:243-248.
  3. Razzaghi MR, Razi A, Mazloomfard MM, Golmohammadi Taklimi A, Valipour R, Razzaghi Z: Safety and efficacy of pneumatic lithotripters versus holmium laser in management of ureteral calculi: a randomized clinical trial. Urol J 2013;10:762-766.
  4. Lee J, Gianduzzo TR: Advances in laser technology in urology. Urol Clin North Am 2009;36:189-198.
  5. Akdeniz E, Irkılata L, Demirel HC, Saylık A, Bolat MS, Şahinkaya N, Zengin M, Atilla MK: A comparison of efficacies of holmium YAG laser, and pneumatic lithotripsy in the endoscopic treatment of ureteral stones. Turk J Urol 2014;40:138-143.
  6. Degirmenci T, Gunlusoy B, Kozacioglu Z, Arslan M, Koras O, Arslan B, Minareci S: Comparison of Ho:YAG laser and pneumatic lithotripsy in the treatment of impacted ureteral stones: an analysis of risk factors. Kaohsiung J Med Sci 2014;30:153-158.
  7. Manohar T, Ganpule A, Desai M: Comparative evaluation of Swiss LithoClast 2 and holmium:YAG laser lithotripsy for impacted upper-ureteral stones. J Endourol 2008;22:443-446.
  8. Yin X, Tang Z, Yu B, Wang Y, Li Y, Yang Q, Tang W: Holmium: YAG laser lithotripsy versus pneumatic lithotripsy for treatment of distal ureteral calculi: a meta-analysis. J Endourol 2013;27:408-414.
  9. Begg CB, Mazumdar M: Operating characteristics of a rank correlation test for publication bias. Biometrics 1994;50:1088-1101.
  10. Song F, Gilbody S: Bias in meta-analysis detected by a simple, graphical test. Increase in studies of publication bias coincided with increasing use of meta-analysis. BMJ 1998;316:471.
  11. Li L, Pan Y, Weng Z, Bao W, Yu Z, Wang F: A prospective randomized trial comparing pneumatic lithotripsy and holmium laser for management of middle and distal ureteral calculi. J Endourol 2015;29:883-887.
  12. Cimino S, Favilla V, Russo GI, Saita A, Sortino G, Castelli T, Veroux M, Madonia M, Morgia G: Pneumatic lithotripsy versus holmium:YAG laser lithotripsy for the treatment of single ureteral stones: a prospective, single-blinded study. Urol Int 2014;92:468-472.
  13. Kassem A, ElFayoumy H, ElSaied W, ElGammal M, Bedair A: Laser and pneumatic lithotripsy in the endoscopic management of large ureteric stones: a comparative study. Urol Int 2012;88:311-315.
  14. Binbay M, Tepeler A, Singh A, Akman T, Tekinaslan E, Sarilar O, Baykal M, Muslumanoglu AY: Evaluation of pneumatic versus holmium:YAG laser lithotripsy for impacted ureteral stones. Int Urol Nephrol 2011;43:989-995.
  15. Garg S, Mandal AK, Singh SK, Naveen A, Ravimohan M, Aggarwal M, Mete UK, Santosh K: Ureteroscopic laser lithotripsy versus ballistic lithotripsy for treatment of ureteric stones: a prospective comparative study. Urol Int 2009;82:341-345.
  16. Maghsoudi R, Amjadi M, Norizadeh D, Hassanzadeh H: Treatment of ureteral stones: a prospective randomized controlled trial on comparison of Ho:YAG laser and pneumatic lithotripsy. Indian J Urol 2008;24:352-354.
  17. Türk C, Petřík A, Sarica K, Seitz C, Skolarikos A, Straub M, Knoll T: EAU guidelines on diagnosis and conservative management of urolithiasis. Eur Urol 2015;69:468-474.
  18. Kronenberg P, Traxer O: In vitro fragmentation efficiency of holmium: yttrium-aluminum-garnet (YAG) laser lithotripsy - a comprehensive study encompassing different frequencies, pulse energies, total power levels and laser fibre diameters. BJU Int 2014;114:261-267.
  19. Wezel F, Häcker A, Gross AJ, Michel MS, Bach T: Effect of pulse energy, frequency and length on holmium:yttrium-aluminum-garnet laser fragmentation efficiency in non-floating artificial urinary calculi. J Endourol 2010;24:1135-1140.
  20. van Driel ML, De Sutter A, De Maeseneer J, Christiaens T: Searching for unpublished trials in Cochrane reviews may not be worth the effort. J Clin Epidemiol 2009;62:838-844.e3.

Author Contacts

Kunjie Wang

Department of Urology

Institute of Urology, West China Hospital, Sichuan University

Guo Xue Xiang 37, Chengdu, Sichuan 610041 (China)

E-Mail wangkj@scu.edu.cn


Article / Publication Details

First-Page Preview
Abstract of Review

Received: April 18, 2016
Accepted: July 19, 2016
Published online: August 10, 2016
Issue release date: March 2017

Number of Print Pages: 9
Number of Figures: 9
Number of Tables: 2

ISSN: 0042-1138 (Print)
eISSN: 1423-0399 (Online)

For additional information: https://www.karger.com/UIN


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References

  1. Khaladkar S, Modi J, Bhansali M, Dobhada S, Patankar S: Which is the best option to treat large (>1.5 cm) midureteric calculi? J Laparoendosc Adv Surg Tech A 2009;19:501-504.
  2. Wright AE, Rukin NJ, Somani BK: Ureteroscopy and stones: current status and future expectations. World J Nephrol 2014;3:243-248.
  3. Razzaghi MR, Razi A, Mazloomfard MM, Golmohammadi Taklimi A, Valipour R, Razzaghi Z: Safety and efficacy of pneumatic lithotripters versus holmium laser in management of ureteral calculi: a randomized clinical trial. Urol J 2013;10:762-766.
  4. Lee J, Gianduzzo TR: Advances in laser technology in urology. Urol Clin North Am 2009;36:189-198.
  5. Akdeniz E, Irkılata L, Demirel HC, Saylık A, Bolat MS, Şahinkaya N, Zengin M, Atilla MK: A comparison of efficacies of holmium YAG laser, and pneumatic lithotripsy in the endoscopic treatment of ureteral stones. Turk J Urol 2014;40:138-143.
  6. Degirmenci T, Gunlusoy B, Kozacioglu Z, Arslan M, Koras O, Arslan B, Minareci S: Comparison of Ho:YAG laser and pneumatic lithotripsy in the treatment of impacted ureteral stones: an analysis of risk factors. Kaohsiung J Med Sci 2014;30:153-158.
  7. Manohar T, Ganpule A, Desai M: Comparative evaluation of Swiss LithoClast 2 and holmium:YAG laser lithotripsy for impacted upper-ureteral stones. J Endourol 2008;22:443-446.
  8. Yin X, Tang Z, Yu B, Wang Y, Li Y, Yang Q, Tang W: Holmium: YAG laser lithotripsy versus pneumatic lithotripsy for treatment of distal ureteral calculi: a meta-analysis. J Endourol 2013;27:408-414.
  9. Begg CB, Mazumdar M: Operating characteristics of a rank correlation test for publication bias. Biometrics 1994;50:1088-1101.
  10. Song F, Gilbody S: Bias in meta-analysis detected by a simple, graphical test. Increase in studies of publication bias coincided with increasing use of meta-analysis. BMJ 1998;316:471.
  11. Li L, Pan Y, Weng Z, Bao W, Yu Z, Wang F: A prospective randomized trial comparing pneumatic lithotripsy and holmium laser for management of middle and distal ureteral calculi. J Endourol 2015;29:883-887.
  12. Cimino S, Favilla V, Russo GI, Saita A, Sortino G, Castelli T, Veroux M, Madonia M, Morgia G: Pneumatic lithotripsy versus holmium:YAG laser lithotripsy for the treatment of single ureteral stones: a prospective, single-blinded study. Urol Int 2014;92:468-472.
  13. Kassem A, ElFayoumy H, ElSaied W, ElGammal M, Bedair A: Laser and pneumatic lithotripsy in the endoscopic management of large ureteric stones: a comparative study. Urol Int 2012;88:311-315.
  14. Binbay M, Tepeler A, Singh A, Akman T, Tekinaslan E, Sarilar O, Baykal M, Muslumanoglu AY: Evaluation of pneumatic versus holmium:YAG laser lithotripsy for impacted ureteral stones. Int Urol Nephrol 2011;43:989-995.
  15. Garg S, Mandal AK, Singh SK, Naveen A, Ravimohan M, Aggarwal M, Mete UK, Santosh K: Ureteroscopic laser lithotripsy versus ballistic lithotripsy for treatment of ureteric stones: a prospective comparative study. Urol Int 2009;82:341-345.
  16. Maghsoudi R, Amjadi M, Norizadeh D, Hassanzadeh H: Treatment of ureteral stones: a prospective randomized controlled trial on comparison of Ho:YAG laser and pneumatic lithotripsy. Indian J Urol 2008;24:352-354.
  17. Türk C, Petřík A, Sarica K, Seitz C, Skolarikos A, Straub M, Knoll T: EAU guidelines on diagnosis and conservative management of urolithiasis. Eur Urol 2015;69:468-474.
  18. Kronenberg P, Traxer O: In vitro fragmentation efficiency of holmium: yttrium-aluminum-garnet (YAG) laser lithotripsy - a comprehensive study encompassing different frequencies, pulse energies, total power levels and laser fibre diameters. BJU Int 2014;114:261-267.
  19. Wezel F, Häcker A, Gross AJ, Michel MS, Bach T: Effect of pulse energy, frequency and length on holmium:yttrium-aluminum-garnet laser fragmentation efficiency in non-floating artificial urinary calculi. J Endourol 2010;24:1135-1140.
  20. van Driel ML, De Sutter A, De Maeseneer J, Christiaens T: Searching for unpublished trials in Cochrane reviews may not be worth the effort. J Clin Epidemiol 2009;62:838-844.e3.
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