REVIEW URRENT C OPINION
Antiretropulsion devices Fernando J. Cabrera, Glenn M. Preminger, and Michael E. Lipkin
Purpose of review Stone migration during the treatment of ureteral stones can prove frustrating and increases both healthcare cost and patient morbidity. Antiretropulsion devices have been engineered to prevent stone migration. Recent findings Improvements in antiretropulsion devices allow for efficient prevention of stone migration during ureteroscopic lithotripsy with minimal adverse effects or complications. Multiple devices are now available each with advantages and disadvantages. New devices are currently engineered to prevent stone migration and maintain ureteral access. Antiretropulsion devices appear to be cost-effective to prevent stone migration during intracorporeal lithotripsy. Summary Antiretropulsion devices have been safely and effectively used during ureteroscopic procedures. These tools increase stone-free rates, decrease morbidity and new studies have demonstrated their cost-effectiveness. Keywords antiretropulsion devices, lithotripsy, shock wave lithotripsy, stone migration, stone retropulsion, ureteroscopy
INTRODUCTION Current guidelines support the use of ureteroscopic lithotripsy as first-line treatment of ureteral stones that fail to pass spontaneously or after shock wave lithotripsy (SWL) failure [1]. Advances in equipment and technique have demonstrated improved success and lower complication rates [2]. Proximal stone migration or stone retropulsion consists of retrograde migration of stone fragments during lithotripsy. Stone retropulsion is relatively common, and has been reported in up to 15% of distal ureteral stones and 48% of proximal ureteral stones [3,4]. Several factors can affect the risk of stone retropulsion including stone location, ureteral dilation, high-pressure irrigation and the type of lithotripter used [5]. Migrated stones may result in increased operative times, radiation exposure, secondary procedures, including the need to convert to flexible ureteroscopy. These sequelae of migrated stones may increase patient morbidity and healthcare costs [3,6]. In addition, residual stone fragments may serve as a source of recurrent stone growth, persistent infection and renal colic [7]. This review evaluates the most recent developments regarding devices that prevent stone retropulsion.
ANTIRETROPULSIVE DEVICES Several devices have been engineered to address the problem of retrograde stone migration and work via
mechanical or gel-based blockage when they are deployed proximal to ureteral calculus. These include mechanical devices such as the Stone Cone (Boston Scientific Corp., Natick, Massachusetts, USA), NTrap (Cook Urological, Spencer, Indiana, USA), and the PercSys Accordion (Percutaneous System, Palo Alto, California, USA). The Escape Basket (Boston Scientific Corp., Natick, Massachusetts, USA) is specifically designed to entrap stones and allow for simultaneous laser lithotripsy thereby preventing proximal migration. Other baskets that prevent retropulsion include the Passport balloon, Parachute and the LithoCatch (Boston Scientific Corp., Natick, Massachusetts, USA). Recently, the BackStop gel (Boston Scientific Corp, Natick, Massachusetts, USA) has been introduced, which forms a plug proximal to the ureteral calculus [8,9]. The table summarizes and describes each antiretropulsive device (Table 1).
Comprehensive Kidney Stone Center Duke University Medical Center Durham, North Carolina, USA Correspondence to Glenn M. Preminger, MD, Comprehensive Kidney Stone Center, Duke University Medical Center, DUMC 3167, Division of Urologic Surgery, Durham, NC 27710, USA. Tel: +1 919 681 5506; fax: +1 919 681 5507; e-mail: [email protected] Curr Opin Urol 2014, 24:173–178 DOI:10.1097/MOU.0000000000000032
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KEY POINTS Antitretropulsive devices aim to prevent stone retropulsion, which is a common problem during treatment of ureteral stones. Stone retropulsion can increase patient morbidity and healthcare costs. Many modern commercially available devices have been safely and effectively used during ureteroscopic procedures. These devices have demonstrated decreasing stone migration and increasing stone-free rate after ureteroscopy. New devices currently being developed will be costeffective, efficient and will serve multiple purposes. Cost-efficiency of antiretropulsion devices may be justified given high cost of auxiliary procedures.
Escape Escape is a zero-tip, four-wire Nitinol stone retrieval basket. Compared with traditional stone baskets, the smaller diameter of Escape provides improved irrigation during lithotripsy. The basket comes with a Y adapter for the ureteroscope working channel that allows simultaneous passage of the laser fiber alongside the basket. The stone can be fragmented while engaged in the basket, thus preventing migration [10]. The Escape facilitates rotation of the stone within the wires to enable accurate localization of the laser energy. This device lacks compatibility with pneumatic or ultrasound lithotripters [11]. Some investigators have reported adequate stone-free rates while using the Escape. Limitations include basket wire damage from laser lithotripsy and the device not working if the stone was not engaged completely within the basket [10].
Lithocatch and Parachute The Lithocatch and Parachute are stone retrieval baskets that can be placed above the ureteral stone to prevent migration. Lithocatch is a wire helical mesh basket and the Parachute is a multiwire stone retrieval device. These devices require an extra wire in the ureter as the ureteroscope would need to be passed alongside the preplaced basket. In addition, these baskets may be too narrow for dilated ureters, allowing stones to flee into the collecting system [10,12].
Passport The device consists of a noncompliant balloon that can be inflated to prevent migration of fragments. It 174
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can also prevent irrigation fluid to flow proximal to the balloon. The balloon is mounted on a guidewire and can be placed proximal to the stone through a ureteroscope under direct vision. Studies have shown adequate stone-free rates and minimal stone retropulsion using the device. The device has been ineffective for dilated ureters [13].
Stone Cone The Stone Cone consists of a stainless steel wire wound with a strand of Nitinol and is baked in a mold to produce a spiral form at the distal tip. During introduction, the coil lies straight inside the carrying catheter. Advancing the double strand wire beyond the tip of the carrying catheter deploys the cone. The catheter can be placed under direct vision through the working channel of an ureteroscope or under fluoroscopic guidance through a cystoscope similar to a guide wire. Once the distal tip of the catheter is beyond the stone, the cone is deployed and used to prevent proximal migration of the stone. The deployed Stone Cone prevents retropulsion of greater than 1.5 mm fragments and can be used to extract small residual fragments by sweeping them down the ureter [14]. Initial reports demonstrated safety and efficacy of the Stone Cone device in preventing stone retropulsion [15,16]. Initial ex-vivo and in-vitro results shows adequate prevention of stone fragment retropulsion. Clinical studies have confirmed an increase in stone-free rates and minimal stone retropulsion with the Stone Cone compared with control groups [4,17,18].
NTrap The NTtrap stone occlusion device has been designed to prevent proximal migration of stones and facilitate fragment extraction during ureteroscopic lithotripsy. The device has a shaft consisting of a wire mesh net composed of tightly woven Nitinol wires within a sheath. The inner wires are 1 mm apart and outer wires 2 mm apart [19]. In a randomized control trial to evaluate the efficiency of NTrap for the treatment of proximal ureteral stones, Wang et al. reported a 0% rate of stone retropulsion with the NTrap group compared to 12% in the non-NTrap group. Despite no visible retropulsion for the NTrap group it failed to achieve statistically significant differences in stonefree rates at follow-up (100 vs. 91.2%, P ¼ 0.098). Reviewers suspect this was due to a small sample size [19]. In a recent study Feng et al. [20 ] published a retrospective study of 156 patients treated with &
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Antiretropulsion devices Cabrera et al. Table 1. Antiretropulsive devices Device
Manufacturer
Description
Comments
Escape
Boston Scientific Corp.
Retrieval basket and simultaneous laser lithotripsy
Possible damage of basket during laser lithotripsy
Lithocatch
Boston Scientific Corp.
Retrieval helical mesh basket
Basket too narrow for dilated ureters
Parachute
Boston Scientific Corp.
Retrieval multiwire basket
Basket too narrow for dilated ureters
Passport
Boston Scientific Corp.
Noncompliant balloon, when inflated prevents retropulsion
Balloon too narrow for dilated ureters
Stone Cone
Boston Scientific Corp.
Stainless steel wire wound with nitonol to produce a spiral form deployed passed the stone to prevent retropulsion and aid retrieval
Prevents retropulsion of >1.5 mm fragments
NTrap
Cook Urological
Wire mesh net composed of tightly woven nitonol wires
Has a 7 mm umbrella design basket to also aid in stone removal
Accordion
Percutaneous System
Hydrophilic microcatheter with a film occlusion device that acts as a backstop
Resistant to damage from lithotripsy also aids in retrieval
BackStop
Boston Scientific Corp.
Water-soluble biocompatible polymer with reverse thermo sensitive properties
Lithotripsy performed without additional devices and wires
XenX
Xenolith Medical
Sieving element composed of braided nitonol wires, with a floppy tip that allows for stent placement
New device/clinical studies pending
NTrap and 152 patients treated without NTrap during holmium laser lithotripsy. The NTrap group achieved lower operative times, and improved stone-free rates. A recently published meta-analysis by Ding et al. [21 ] pooled 456 patients from two randomized control trials and one case–control study. The use of NTrap demonstrated a significant advantage in terms of lower stone-free rate, stone migration and auxiliary procedures compared with control. There was not a significant difference in operative times between the two groups. &
PercSys Accordion The Accordion is a recently developed device with a hydrophilic microcatheter-based tool with a film occlusion mechanism that acts as a ureteral backstop once deployed. It is deployed by coaxial retraction of the inner core of the coaxial wire, it ‘accordions’ to a 7-mm or 10-mm wide device that blocks stone migration and provides the utility of a basket during stone fragment removal [22]. In-vitro studies performed in ureteral models demonstrated the efficacy and safety of the Accordion device. They also showed that the device was not damaged by lithotripsy [6,23]. Clinical studies showed a significant reduction in retrograde migration of fragments vs. control. They also noted faster fragmentation times and less passes with the ureteroscope to effectively remove all stone fragments [24 ]. &
&&
Wu et al. [25 ] recently published their experience using the Accordion device. They performed a retrospective review and focused on three main endpoints: operating time, fluoroscopy time and stone-free rates. They analyzed 235 cases of ureteral stones treated with ureteroscopy. Of these cases, the Accordion device was used in 32% of cases, primarily for distal ureteral stones. Their review showed that there was no difference in fluoroscopy, operative time and complication rate. There was a significant difference in stone-free rate between the Accordion and non-Accordion groups on postoperative imaging. The stone-free rate for the Accordion group was significantly higher (84.2 vs. 53.6%, P ¼ 0.001). The Accordion device improved the stone-free rate by 30.6% in univariate analysis. In multivariate logistic regression, the odds ratio of being stone-free when the Accordion device was used was 4.35. They concluded that the Accordion antiretropulsion device is safely used during ureteroscopic lithotripsy and it improves stone-free status. They recommend further prospective studies to validate their results. A limitation was that they did not report auxiliary procedures and stone migration rate post ureteroscopy, so it is unclear if stone-free status was due to prevention of retropulsion.
Lubricating/lidocaine jelly High viscosity, jelly-like materials have been placed proximal to ureteral stones to prevent stone migration. Some researchers have reported decreased stone
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migration using lidocaine jelly compared with control [26,27]. Difficulties reported include material washout by irrigation and problems with jelly flowing into the lens of the ureteroscope thereby effecting visualization [27].
procedures compared with NTrap and control groups. They report that for some cases the 7 mm diameter of the NTrap was not wide enough to keep some fragments from migrating.
NEW DEVICES BackStop BackStop is a water-soluble biocompatible polymer with reverse thermosensitive properties. It exists as a liquid at temperatures below 16 8C and as a soft but injectable gel at room temperature, which then transitions to a viscous gel at body temperature. The gel is injected via a ureteric catheter and released above the stone to form a gel plug that conforms to the shape of the ureter, preventing stone migration. The ureteric catheter can be placed through the working channel of the ureteroscope or under fluoroscopic guidance through a cystoscope. Upon completion of stone fragmentation, the BackStop is dissolved using cold physiological saline irrigation [9]. In a prospective, randomized, single-blind, multicenter controlled clinical study, Rane et al. [9] reported on the efficiency on BackStop in preventing stone retropulsion. The BackStop significantly reduced the rate of retropulsion compared with no antiretropulsion device (8.8 vs. 52.9%). There was no improvement seen in stone-free rate between groups, which the authors attribute to an underpowered study. A more recent review reported seven ureteroscopic procedures for distal ureteral stones treated with laser lithotripsy and BackStop at a single center. They reported no stone retropulsion and 100% of patients were rendered stone-free. An advantage reported was the clean endoscopic field, free of secondary devices. This study did not have any control groups and had a very small sample size [28].
COMPARATIVE STUDIES In-vitro studies have shown similar safety and efficiency between devices [29]. In a randomized controlled trial comparing the use of NTrap and Stone Cone during pneumatic lithothripsy of proximal ureteral stones, Farahat et al. [30] reported adequate safety and efficiency of both devices. A total of 195 patients were randomized to Stone Cone, NTrap and control (no ureteral occlusion device). Stone-free rates at 3 weeks were 95.2, 83.05 and 72.4% for the Stone Cone, NTrap and control, respectively. Auxilliary procedures were performed in 4.7, 16.9 and 27.5% for the Stone Cone, NTrap and control, respectively. The Stone Cone group showed significant lowered stone migration, increased stone-free rate and decreased auxiliary 176
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Currently, none of the available stone migration devices can serve the dual purpose of an occlusion device and a guidewire over which a stent can be placed at the completion of the procedure. Sarkissian et al. [31 ] has recently published an initial ex vivo study on a new ureteral occlusion device that can serve this purpose. XenX (Xenolith Medical) is characterized by a 5-cm-long sieving element composed of 42 braided Nitinol wires that self-expand to the shape of the ureter 10 or 12 mm in diameter, and a 15-cm floppy tip that allows for stone passage and coiling in the renal pelvis during stent placement. An 80-cm-long, 0.040-in outer sheath reinforced with stainless steel is used to deploy the sieving element when desired by holding the 150-cm Nitinol core wire and pulling back the sheath. In an ex-vivo porcine model the XenX was compared with commercially available antiretropulsive devices and guidewires. No gross ureteral trauma or diffierence in microscopic denudation was observed between the XenX and the other devices. The force required to pass through the ureteral stone using the XenX was minimal. The NTrap required the greatest force when attempting to navigate past a stone (P ¼ .0003), followed by the Stone Cone (P ¼ .009), with little difference among the other devices (P ¼ .72). The XenX achieved superior antiretropulsion in the 4 mm and 10 mm models as compared with the other devices. Ureteral stents were placed successfully over the rigid shaft of the XenX. A limitation of the study was that they did not include the Accordion device in their evaluation. The advantage of this product relies on the ability to occupy a dilated and tortuous ureter and maintain access for the placement of a ureteral stent. Furthermore, in-vivo comparative studies are required. &&
COST-EFFECTIVENESS Cost-effectiveness and resource allocation is an important part of current medical practice. According to Dretler [13] the cost of the Stone Cone device (approximately US$250) outweighs the expense of an auxiliary procedure and its use is recommended for lower ureteral stones. This assumption has been solidified by recent data from Ursiny and Eisner [32 ]. They used current published data on &&
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Antiretropulsion devices Cabrera et al.
antiretropulsive devices compared with control groups. With these data, the authors published a decision analysis to determine if the use of aniretropulsive devices is cost-effective. They reviewed current and commercially available antiretropulsion devices including BackStop, NTrap, Stone Cone and Lidocaine jelly. They made three basic assumptions as follows: ureteroscopy with pneumatic or holium laser lithotripsy was the initial treatment, patients with retropulsed stones would undergo auxillary procedures, these procedures would include ureteroscopy in 50% and SWL in the remaining 50%. The individual average device cost was $278. The estimated costs of auxiliary procedures were $5290 and $6390 for ureteroscopy and SWL, respectively. Retropulsion rate was 1.9 vs. 16.3% of control. Their decision analysis showed that the use of an anitretropulsive device would be cost-effective at a retropulsion rate of more than 6.3%. The study did not capture patients that underwent flexible ureteroscopy for the treatment of retropulsed stones. The use of the flexible ureteroscope would increase cost and would underestimate their model. The main limitation of the study lies in its main assumption that patients who experienced retropulsed stones would undergo secondary procedures.
CONCLUSION Retropulsed stones are a source of patient morbidity and increased healthcare costs. Antiretropulsion devices have aimed to prevent and minimize stone retropulsion. Recently published data have attempted to review the safety, efficiency and cost-effectiveness of these devices. Each device has advantages and disadvantages that will have to be factored into each clinical scenario. These devices should prevent stone migration, be easily handled by the surgeon and be resistant to damage from lithotripsy. Given the rising healthcare costs these devices should be cost-effective. Given the right rates of retropulsion during ureteroscopy, which may lead to prolonged or secondary procedures, routine use of antiretropulsion devices appear to be a cost-effective. This is important for urologists who mainly use pneumatic lithotripters and have limited access to flexible ureteroscopes. Acknowledgements This manuscript has been seen, reviewed and approved by all contributing authors. Conflicts of interest F.C. has no disclosures.
G.M.P. serves as a consultant for Boston Scientific and Mission Pharmacal. M.L. serves as a consultant for Boston Scientific.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Bader MJ, Eisner B, Porpiglia F, Preminger G, et al. Contemporary management of ureteral stones. Eur Urol 2012; 61:764–772. 2. Preminger GM, Tiselius HG, Assimos DG, et al. 2007 Guideline for the management of ureteral calculi. Eur Urol 2007; 52:1610–1631. 3. Chow GK, Patterson DE, Blute ML, et al. Ureteroscopy: effect of technology and technique on clinical practice. J Urol 2003; 170:99–102. 4. Eisner BH, Dretler SP. Use of the Stone Cone for prevention of calculus retropulsion during holmium : YAG laser lithotripsy: case series and review of the literature. Urol Int 2009; 82:356–360. 5. Sun Y, Wang L, Liao G, et al. Pneumatic lithotripsy versus laser lithotripsy in the endoscopic treatment of ureteral calculi. J Endourol 2001; 15:587–590. 6. Eisner BH, Pengune W, Stoller ML, et al. Use of an antiretropulsion device to prevent stone retropulsion significantly increases the efficiency of pneumatic lithotripsy: an in vitro study. BJU Int 2009; 104:858–861. 7. Delvecchio FC, Preminger GM. Management of residual stones. Urol Clin North Am 2000; 27:347–354. 8. Rane A, Sur R, Chew B. Retropulsion during intracorporeal lithotripsy: what’s out there to help? BJU Int 2010; 106:591–592. 9. Rane A, Bradoo A, Rao P, et al. The use of a novel reverse thermosensitive polymer to prevent ureteral stone retropulsion during intracorporeal lithotripsy: a randomized, controlled trial. J Urol 2010; 183:1417–1421. 10. Kesler SS, Pierre SA, Brison DI, et al. Use of the Escape nitinol stone retrieval basket facilitates fragmentation and extraction of ureteral and renal calculi: a pilot study. J Endourol 2008; 22:1213–1217. 11. Elashry OM, Tawfik AM. Preventing stone retropulsion during intracorporeal lithotripsy. Nat Rev Urol 2012; 9:691–698. 12. el-Gabry EA, Bagley DH. Retrieval capabilities of different stone basket designs in vitro. J Endourol 1999; 13:305–307. 13. Dretler SP. Ureteroscopy for proximal ureteral calculi: prevention of stone migration. J Endourol 2000; 14:565–567. 14. Dretler SP. The stone cone: a new generation of basketry. J Urol 2001; 165:1593–1596. 15. Desai MR, Patel SB, Desai MM, et al. The Dretler stone cone: a device to prevent ureteral stone migration – the initial clinical experience. J Urol 2002; 167:1985–1988. 16. Maislos SD, Volpe M, Albert PS, et al. Efficacy of the Stone Cone for treatment of proximal ureteral stones. J Endourol 2004; 18:862–864. 17. Gonen M, Cenker A, Istanbulluoglu O, et al. Efficacy of Dretler stone cone in the treatment of ureteral stones with pneumatic lithotripsy. Urol Int 2006; 76:159–162. 18. Pardalidis NP, Papatsoris AG, Kosmaoglou EV. Prevention of retrograde calculus migration with the Stone Cone. Urol Res 2005; 33:61–64. 19. Wang CJ, Huang SW, Chang CH. Randomized trial of NTrap for proximal ureteral stones. Urology 2011; 77:553–557. 20. Feng C, Ding Q, Jiang H, et al. Use of NTrap during ureteroscopic Holmiu& m : YAG laser lithotripsy of upper ureteral calculi. Minim Invasive Ther Allied Technol 2012; 21:78–82. Intraoperative stone migration is a major problem during Ho : YAG laser lithotripsy of upper ureteral calculi. A retroscpective study of 308 patients treated with ureteroscopy with and without NTrap was performed. Patients treated with NTrap had a higher intraoperative success of lithotripsy and a lower postoperative stone residual rate. They found longer operative times with the NTrap group, but the device was safely and effectively used during ureteroscopic procedures . 21. Ding H, Wang Z, Du W, et al. NTrap in prevention of stone migration & during ureteroscopic lithotripsy for proximal ureteral stones: a meta-analysis. J Endourol 2012; 26:130–134. The authors evaluated the effectiveness of NTrap in the prevention of stone migration during ureteroscopic lithotripsy for proximal ureteral stones. They evaluated two randomized controlled trials and one case–control trial including 456 patients. The NTrap group showed an advantage in stone free rates, lower stone migration and decreased auxiliary SWL. The authors recommend further higher quality randomized controlled trials. 22. Wosnitzer M, Xavier K, Gupta M. Novel use of a ureteroscopic stone entrapment device to prevent antegrade stone migration during percutaneous nephrolithotomy. J Endourol 2009; 23:203–207. 23. Olbert PJ, Keil C, Weber J, et al. Efficacy and safety of the Accordion stonetrapping device: in vitro results from an artificial ureterolithotripsy model. Urol Res 2010; 38:41–46.
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Urolithiasis 24. Pagnani CJ, El Akkad M, Bagley DH. Prevention of stone migration with the Accordion during endoscopic ureteral lithotripsy. J Endourol 2012; 26:484– 488. The purpose of the authors was to analyze the effect of the Accordion on stone migration and overall efficiency during lithotripsy. They prospectively analyzed 21 patients treated for 23 distal ureteral stones. The Accordion was randomly used in 11 of these 21 patients. Patients who were treated with the Accordion device experienced less retrograde migration during fragmentation (P ¼ 0.0064). 25. Wu JA, Ngo TC, Hagedorn JC, et al. The accordion antiretropulsive device && improves stone-free rates during ureteroscopic laser lithotripsy. J Endourol 2013; 27:438–441. The authors describe their experience with the Accordion device focusing on three main endpoints: operating time, fluoroscopy time and stone-free rates. They performed a retrospective review including 235 cases undergoing ureteroscopy for ureteral stones. Accordion device usage was not associated with a significant reduction in fluoroscopy time or operating time. However, the stone-free rate for the Accordion group was significantly higher compared to the non-Accordion group (84.2 vs. 53.6%, P ¼ 0.001). Therefore, the authors conclude that the Accordion device improved stone-free rates during ureteroscopic lithotripsy. 26. Mohseni MG, Arasteh S, Alizadeh F. Preventing retrograde stone displacement during pneumatic lithotripsy for ureteral calculi using lidocaine jelly. Urology 2006; 68:505–507. 27. Zehri AA, Ather MH, Siddiqui KM, et al. A randomized clinical trial of lidocaine jelly for prevention of inadvertent retrograde stone migration during pneumatic lithotripsy of ureteral stone. J Urol 2008; 180:966–968. &
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28. Molina WR, Pompeo A, Sehrt D, et al. Use of a polymeric gel to prevent retropulsion during intracorporeal lithotripsy. Actas Urol Esp 2013; 37:188–192. 29. Ahmed M, Pedro RN, Kieley S, et al. Systematic evaluation of ureteral occlusion devices: insertion, deployment, stone migration, and extraction. Urology 2009; 73:976–980. 30. Farahat YA, Elbahnasy AE, Elashry OM. A randomized prospective controlled study for assessment of different ureteral occlusion devices in prevention of stone migration during pneumatic lithotripsy. Urology 2011; 77:30–35. 31. Sarkissian C, Paz A, Zigman O, et al. Safety and efficacy of a novel ureteral && occlusion device. Urology 2012; 80:32–37. The authors evaluated the safety of a novel ureteral occlusion device and compared its performance with that of other devices and guidewires. They used an ex-vivo porcine model to evaluate urothelium trauma, stone migration and the ability use the device for stent placement. They also used an in-vitro model to compare insertion forces and maneuverability. The XenX prevented stone migration with minimal insertion forces and allowed for stent placement. The authors recommend further clinical studies. 32. Ursiny M, Eisner BH. Cost-effectiveness of antiretropulsion devices for && ureteroscopic lithotripsy. J Urol 2013; 189:1762–1766. The authors evaluated the cost-effectiveness of antiretropulsion devices used during ureteroscopic lithotripsy. A decision analysis model was constructed to compare the cost-effectiveness of ureteroscopic lithotripsy with vs. without an antiretropulsion device. The estimated costs of secondary procedures needed to treat retropulsed stones averaged $5840. The probability of retropulsion without an antiretropulsion device is 16.3%. It became cost-effective to use an antiretropulsion device at or above a 6.3% retropulsion rate.
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Antiretropulsion devices Fernando J. Cabrera, Glenn M. Preminger, and Michael E. Lipkin
Purpose of review Stone migration during the treatment of ureteral stones can prove frustrating and increases both healthcare cost and patient morbidity. Antiretropulsion devices have been engineered to prevent stone migration. Recent findings Improvements in antiretropulsion devices allow for efficient prevention of stone migration during ureteroscopic lithotripsy with minimal adverse effects or complications. Multiple devices are now available each with advantages and disadvantages. New devices are currently engineered to prevent stone migration and maintain ureteral access. Antiretropulsion devices appear to be cost-effective to prevent stone migration during intracorporeal lithotripsy. Summary Antiretropulsion devices have been safely and effectively used during ureteroscopic procedures. These tools increase stone-free rates, decrease morbidity and new studies have demonstrated their cost-effectiveness. Keywords antiretropulsion devices, lithotripsy, shock wave lithotripsy, stone migration, stone retropulsion, ureteroscopy
INTRODUCTION Current guidelines support the use of ureteroscopic lithotripsy as first-line treatment of ureteral stones that fail to pass spontaneously or after shock wave lithotripsy (SWL) failure [1]. Advances in equipment and technique have demonstrated improved success and lower complication rates [2]. Proximal stone migration or stone retropulsion consists of retrograde migration of stone fragments during lithotripsy. Stone retropulsion is relatively common, and has been reported in up to 15% of distal ureteral stones and 48% of proximal ureteral stones [3,4]. Several factors can affect the risk of stone retropulsion including stone location, ureteral dilation, high-pressure irrigation and the type of lithotripter used [5]. Migrated stones may result in increased operative times, radiation exposure, secondary procedures, including the need to convert to flexible ureteroscopy. These sequelae of migrated stones may increase patient morbidity and healthcare costs [3,6]. In addition, residual stone fragments may serve as a source of recurrent stone growth, persistent infection and renal colic [7]. This review evaluates the most recent developments regarding devices that prevent stone retropulsion.
ANTIRETROPULSIVE DEVICES Several devices have been engineered to address the problem of retrograde stone migration and work via
mechanical or gel-based blockage when they are deployed proximal to ureteral calculus. These include mechanical devices such as the Stone Cone (Boston Scientific Corp., Natick, Massachusetts, USA), NTrap (Cook Urological, Spencer, Indiana, USA), and the PercSys Accordion (Percutaneous System, Palo Alto, California, USA). The Escape Basket (Boston Scientific Corp., Natick, Massachusetts, USA) is specifically designed to entrap stones and allow for simultaneous laser lithotripsy thereby preventing proximal migration. Other baskets that prevent retropulsion include the Passport balloon, Parachute and the LithoCatch (Boston Scientific Corp., Natick, Massachusetts, USA). Recently, the BackStop gel (Boston Scientific Corp, Natick, Massachusetts, USA) has been introduced, which forms a plug proximal to the ureteral calculus [8,9]. The table summarizes and describes each antiretropulsive device (Table 1).
Comprehensive Kidney Stone Center Duke University Medical Center Durham, North Carolina, USA Correspondence to Glenn M. Preminger, MD, Comprehensive Kidney Stone Center, Duke University Medical Center, DUMC 3167, Division of Urologic Surgery, Durham, NC 27710, USA. Tel: +1 919 681 5506; fax: +1 919 681 5507; e-mail: [email protected] Curr Opin Urol 2014, 24:173–178 DOI:10.1097/MOU.0000000000000032
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Urolithiasis
KEY POINTS Antitretropulsive devices aim to prevent stone retropulsion, which is a common problem during treatment of ureteral stones. Stone retropulsion can increase patient morbidity and healthcare costs. Many modern commercially available devices have been safely and effectively used during ureteroscopic procedures. These devices have demonstrated decreasing stone migration and increasing stone-free rate after ureteroscopy. New devices currently being developed will be costeffective, efficient and will serve multiple purposes. Cost-efficiency of antiretropulsion devices may be justified given high cost of auxiliary procedures.
Escape Escape is a zero-tip, four-wire Nitinol stone retrieval basket. Compared with traditional stone baskets, the smaller diameter of Escape provides improved irrigation during lithotripsy. The basket comes with a Y adapter for the ureteroscope working channel that allows simultaneous passage of the laser fiber alongside the basket. The stone can be fragmented while engaged in the basket, thus preventing migration [10]. The Escape facilitates rotation of the stone within the wires to enable accurate localization of the laser energy. This device lacks compatibility with pneumatic or ultrasound lithotripters [11]. Some investigators have reported adequate stone-free rates while using the Escape. Limitations include basket wire damage from laser lithotripsy and the device not working if the stone was not engaged completely within the basket [10].
Lithocatch and Parachute The Lithocatch and Parachute are stone retrieval baskets that can be placed above the ureteral stone to prevent migration. Lithocatch is a wire helical mesh basket and the Parachute is a multiwire stone retrieval device. These devices require an extra wire in the ureter as the ureteroscope would need to be passed alongside the preplaced basket. In addition, these baskets may be too narrow for dilated ureters, allowing stones to flee into the collecting system [10,12].
Passport The device consists of a noncompliant balloon that can be inflated to prevent migration of fragments. It 174
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can also prevent irrigation fluid to flow proximal to the balloon. The balloon is mounted on a guidewire and can be placed proximal to the stone through a ureteroscope under direct vision. Studies have shown adequate stone-free rates and minimal stone retropulsion using the device. The device has been ineffective for dilated ureters [13].
Stone Cone The Stone Cone consists of a stainless steel wire wound with a strand of Nitinol and is baked in a mold to produce a spiral form at the distal tip. During introduction, the coil lies straight inside the carrying catheter. Advancing the double strand wire beyond the tip of the carrying catheter deploys the cone. The catheter can be placed under direct vision through the working channel of an ureteroscope or under fluoroscopic guidance through a cystoscope similar to a guide wire. Once the distal tip of the catheter is beyond the stone, the cone is deployed and used to prevent proximal migration of the stone. The deployed Stone Cone prevents retropulsion of greater than 1.5 mm fragments and can be used to extract small residual fragments by sweeping them down the ureter [14]. Initial reports demonstrated safety and efficacy of the Stone Cone device in preventing stone retropulsion [15,16]. Initial ex-vivo and in-vitro results shows adequate prevention of stone fragment retropulsion. Clinical studies have confirmed an increase in stone-free rates and minimal stone retropulsion with the Stone Cone compared with control groups [4,17,18].
NTrap The NTtrap stone occlusion device has been designed to prevent proximal migration of stones and facilitate fragment extraction during ureteroscopic lithotripsy. The device has a shaft consisting of a wire mesh net composed of tightly woven Nitinol wires within a sheath. The inner wires are 1 mm apart and outer wires 2 mm apart [19]. In a randomized control trial to evaluate the efficiency of NTrap for the treatment of proximal ureteral stones, Wang et al. reported a 0% rate of stone retropulsion with the NTrap group compared to 12% in the non-NTrap group. Despite no visible retropulsion for the NTrap group it failed to achieve statistically significant differences in stonefree rates at follow-up (100 vs. 91.2%, P ¼ 0.098). Reviewers suspect this was due to a small sample size [19]. In a recent study Feng et al. [20 ] published a retrospective study of 156 patients treated with &
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Antiretropulsion devices Cabrera et al. Table 1. Antiretropulsive devices Device
Manufacturer
Description
Comments
Escape
Boston Scientific Corp.
Retrieval basket and simultaneous laser lithotripsy
Possible damage of basket during laser lithotripsy
Lithocatch
Boston Scientific Corp.
Retrieval helical mesh basket
Basket too narrow for dilated ureters
Parachute
Boston Scientific Corp.
Retrieval multiwire basket
Basket too narrow for dilated ureters
Passport
Boston Scientific Corp.
Noncompliant balloon, when inflated prevents retropulsion
Balloon too narrow for dilated ureters
Stone Cone
Boston Scientific Corp.
Stainless steel wire wound with nitonol to produce a spiral form deployed passed the stone to prevent retropulsion and aid retrieval
Prevents retropulsion of >1.5 mm fragments
NTrap
Cook Urological
Wire mesh net composed of tightly woven nitonol wires
Has a 7 mm umbrella design basket to also aid in stone removal
Accordion
Percutaneous System
Hydrophilic microcatheter with a film occlusion device that acts as a backstop
Resistant to damage from lithotripsy also aids in retrieval
BackStop
Boston Scientific Corp.
Water-soluble biocompatible polymer with reverse thermo sensitive properties
Lithotripsy performed without additional devices and wires
XenX
Xenolith Medical
Sieving element composed of braided nitonol wires, with a floppy tip that allows for stent placement
New device/clinical studies pending
NTrap and 152 patients treated without NTrap during holmium laser lithotripsy. The NTrap group achieved lower operative times, and improved stone-free rates. A recently published meta-analysis by Ding et al. [21 ] pooled 456 patients from two randomized control trials and one case–control study. The use of NTrap demonstrated a significant advantage in terms of lower stone-free rate, stone migration and auxiliary procedures compared with control. There was not a significant difference in operative times between the two groups. &
PercSys Accordion The Accordion is a recently developed device with a hydrophilic microcatheter-based tool with a film occlusion mechanism that acts as a ureteral backstop once deployed. It is deployed by coaxial retraction of the inner core of the coaxial wire, it ‘accordions’ to a 7-mm or 10-mm wide device that blocks stone migration and provides the utility of a basket during stone fragment removal [22]. In-vitro studies performed in ureteral models demonstrated the efficacy and safety of the Accordion device. They also showed that the device was not damaged by lithotripsy [6,23]. Clinical studies showed a significant reduction in retrograde migration of fragments vs. control. They also noted faster fragmentation times and less passes with the ureteroscope to effectively remove all stone fragments [24 ]. &
&&
Wu et al. [25 ] recently published their experience using the Accordion device. They performed a retrospective review and focused on three main endpoints: operating time, fluoroscopy time and stone-free rates. They analyzed 235 cases of ureteral stones treated with ureteroscopy. Of these cases, the Accordion device was used in 32% of cases, primarily for distal ureteral stones. Their review showed that there was no difference in fluoroscopy, operative time and complication rate. There was a significant difference in stone-free rate between the Accordion and non-Accordion groups on postoperative imaging. The stone-free rate for the Accordion group was significantly higher (84.2 vs. 53.6%, P ¼ 0.001). The Accordion device improved the stone-free rate by 30.6% in univariate analysis. In multivariate logistic regression, the odds ratio of being stone-free when the Accordion device was used was 4.35. They concluded that the Accordion antiretropulsion device is safely used during ureteroscopic lithotripsy and it improves stone-free status. They recommend further prospective studies to validate their results. A limitation was that they did not report auxiliary procedures and stone migration rate post ureteroscopy, so it is unclear if stone-free status was due to prevention of retropulsion.
Lubricating/lidocaine jelly High viscosity, jelly-like materials have been placed proximal to ureteral stones to prevent stone migration. Some researchers have reported decreased stone
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Urolithiasis
migration using lidocaine jelly compared with control [26,27]. Difficulties reported include material washout by irrigation and problems with jelly flowing into the lens of the ureteroscope thereby effecting visualization [27].
procedures compared with NTrap and control groups. They report that for some cases the 7 mm diameter of the NTrap was not wide enough to keep some fragments from migrating.
NEW DEVICES BackStop BackStop is a water-soluble biocompatible polymer with reverse thermosensitive properties. It exists as a liquid at temperatures below 16 8C and as a soft but injectable gel at room temperature, which then transitions to a viscous gel at body temperature. The gel is injected via a ureteric catheter and released above the stone to form a gel plug that conforms to the shape of the ureter, preventing stone migration. The ureteric catheter can be placed through the working channel of the ureteroscope or under fluoroscopic guidance through a cystoscope. Upon completion of stone fragmentation, the BackStop is dissolved using cold physiological saline irrigation [9]. In a prospective, randomized, single-blind, multicenter controlled clinical study, Rane et al. [9] reported on the efficiency on BackStop in preventing stone retropulsion. The BackStop significantly reduced the rate of retropulsion compared with no antiretropulsion device (8.8 vs. 52.9%). There was no improvement seen in stone-free rate between groups, which the authors attribute to an underpowered study. A more recent review reported seven ureteroscopic procedures for distal ureteral stones treated with laser lithotripsy and BackStop at a single center. They reported no stone retropulsion and 100% of patients were rendered stone-free. An advantage reported was the clean endoscopic field, free of secondary devices. This study did not have any control groups and had a very small sample size [28].
COMPARATIVE STUDIES In-vitro studies have shown similar safety and efficiency between devices [29]. In a randomized controlled trial comparing the use of NTrap and Stone Cone during pneumatic lithothripsy of proximal ureteral stones, Farahat et al. [30] reported adequate safety and efficiency of both devices. A total of 195 patients were randomized to Stone Cone, NTrap and control (no ureteral occlusion device). Stone-free rates at 3 weeks were 95.2, 83.05 and 72.4% for the Stone Cone, NTrap and control, respectively. Auxilliary procedures were performed in 4.7, 16.9 and 27.5% for the Stone Cone, NTrap and control, respectively. The Stone Cone group showed significant lowered stone migration, increased stone-free rate and decreased auxiliary 176
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Currently, none of the available stone migration devices can serve the dual purpose of an occlusion device and a guidewire over which a stent can be placed at the completion of the procedure. Sarkissian et al. [31 ] has recently published an initial ex vivo study on a new ureteral occlusion device that can serve this purpose. XenX (Xenolith Medical) is characterized by a 5-cm-long sieving element composed of 42 braided Nitinol wires that self-expand to the shape of the ureter 10 or 12 mm in diameter, and a 15-cm floppy tip that allows for stone passage and coiling in the renal pelvis during stent placement. An 80-cm-long, 0.040-in outer sheath reinforced with stainless steel is used to deploy the sieving element when desired by holding the 150-cm Nitinol core wire and pulling back the sheath. In an ex-vivo porcine model the XenX was compared with commercially available antiretropulsive devices and guidewires. No gross ureteral trauma or diffierence in microscopic denudation was observed between the XenX and the other devices. The force required to pass through the ureteral stone using the XenX was minimal. The NTrap required the greatest force when attempting to navigate past a stone (P ¼ .0003), followed by the Stone Cone (P ¼ .009), with little difference among the other devices (P ¼ .72). The XenX achieved superior antiretropulsion in the 4 mm and 10 mm models as compared with the other devices. Ureteral stents were placed successfully over the rigid shaft of the XenX. A limitation of the study was that they did not include the Accordion device in their evaluation. The advantage of this product relies on the ability to occupy a dilated and tortuous ureter and maintain access for the placement of a ureteral stent. Furthermore, in-vivo comparative studies are required. &&
COST-EFFECTIVENESS Cost-effectiveness and resource allocation is an important part of current medical practice. According to Dretler [13] the cost of the Stone Cone device (approximately US$250) outweighs the expense of an auxiliary procedure and its use is recommended for lower ureteral stones. This assumption has been solidified by recent data from Ursiny and Eisner [32 ]. They used current published data on &&
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Antiretropulsion devices Cabrera et al.
antiretropulsive devices compared with control groups. With these data, the authors published a decision analysis to determine if the use of aniretropulsive devices is cost-effective. They reviewed current and commercially available antiretropulsion devices including BackStop, NTrap, Stone Cone and Lidocaine jelly. They made three basic assumptions as follows: ureteroscopy with pneumatic or holium laser lithotripsy was the initial treatment, patients with retropulsed stones would undergo auxillary procedures, these procedures would include ureteroscopy in 50% and SWL in the remaining 50%. The individual average device cost was $278. The estimated costs of auxiliary procedures were $5290 and $6390 for ureteroscopy and SWL, respectively. Retropulsion rate was 1.9 vs. 16.3% of control. Their decision analysis showed that the use of an anitretropulsive device would be cost-effective at a retropulsion rate of more than 6.3%. The study did not capture patients that underwent flexible ureteroscopy for the treatment of retropulsed stones. The use of the flexible ureteroscope would increase cost and would underestimate their model. The main limitation of the study lies in its main assumption that patients who experienced retropulsed stones would undergo secondary procedures.
CONCLUSION Retropulsed stones are a source of patient morbidity and increased healthcare costs. Antiretropulsion devices have aimed to prevent and minimize stone retropulsion. Recently published data have attempted to review the safety, efficiency and cost-effectiveness of these devices. Each device has advantages and disadvantages that will have to be factored into each clinical scenario. These devices should prevent stone migration, be easily handled by the surgeon and be resistant to damage from lithotripsy. Given the rising healthcare costs these devices should be cost-effective. Given the right rates of retropulsion during ureteroscopy, which may lead to prolonged or secondary procedures, routine use of antiretropulsion devices appear to be a cost-effective. This is important for urologists who mainly use pneumatic lithotripters and have limited access to flexible ureteroscopes. Acknowledgements This manuscript has been seen, reviewed and approved by all contributing authors. Conflicts of interest F.C. has no disclosures.
G.M.P. serves as a consultant for Boston Scientific and Mission Pharmacal. M.L. serves as a consultant for Boston Scientific.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Bader MJ, Eisner B, Porpiglia F, Preminger G, et al. Contemporary management of ureteral stones. Eur Urol 2012; 61:764–772. 2. Preminger GM, Tiselius HG, Assimos DG, et al. 2007 Guideline for the management of ureteral calculi. Eur Urol 2007; 52:1610–1631. 3. Chow GK, Patterson DE, Blute ML, et al. Ureteroscopy: effect of technology and technique on clinical practice. J Urol 2003; 170:99–102. 4. Eisner BH, Dretler SP. Use of the Stone Cone for prevention of calculus retropulsion during holmium : YAG laser lithotripsy: case series and review of the literature. Urol Int 2009; 82:356–360. 5. Sun Y, Wang L, Liao G, et al. Pneumatic lithotripsy versus laser lithotripsy in the endoscopic treatment of ureteral calculi. J Endourol 2001; 15:587–590. 6. Eisner BH, Pengune W, Stoller ML, et al. Use of an antiretropulsion device to prevent stone retropulsion significantly increases the efficiency of pneumatic lithotripsy: an in vitro study. BJU Int 2009; 104:858–861. 7. Delvecchio FC, Preminger GM. Management of residual stones. Urol Clin North Am 2000; 27:347–354. 8. Rane A, Sur R, Chew B. Retropulsion during intracorporeal lithotripsy: what’s out there to help? BJU Int 2010; 106:591–592. 9. Rane A, Bradoo A, Rao P, et al. The use of a novel reverse thermosensitive polymer to prevent ureteral stone retropulsion during intracorporeal lithotripsy: a randomized, controlled trial. J Urol 2010; 183:1417–1421. 10. Kesler SS, Pierre SA, Brison DI, et al. Use of the Escape nitinol stone retrieval basket facilitates fragmentation and extraction of ureteral and renal calculi: a pilot study. J Endourol 2008; 22:1213–1217. 11. Elashry OM, Tawfik AM. Preventing stone retropulsion during intracorporeal lithotripsy. Nat Rev Urol 2012; 9:691–698. 12. el-Gabry EA, Bagley DH. Retrieval capabilities of different stone basket designs in vitro. J Endourol 1999; 13:305–307. 13. Dretler SP. Ureteroscopy for proximal ureteral calculi: prevention of stone migration. J Endourol 2000; 14:565–567. 14. Dretler SP. The stone cone: a new generation of basketry. J Urol 2001; 165:1593–1596. 15. Desai MR, Patel SB, Desai MM, et al. The Dretler stone cone: a device to prevent ureteral stone migration – the initial clinical experience. J Urol 2002; 167:1985–1988. 16. Maislos SD, Volpe M, Albert PS, et al. Efficacy of the Stone Cone for treatment of proximal ureteral stones. J Endourol 2004; 18:862–864. 17. Gonen M, Cenker A, Istanbulluoglu O, et al. Efficacy of Dretler stone cone in the treatment of ureteral stones with pneumatic lithotripsy. Urol Int 2006; 76:159–162. 18. Pardalidis NP, Papatsoris AG, Kosmaoglou EV. Prevention of retrograde calculus migration with the Stone Cone. Urol Res 2005; 33:61–64. 19. Wang CJ, Huang SW, Chang CH. Randomized trial of NTrap for proximal ureteral stones. Urology 2011; 77:553–557. 20. Feng C, Ding Q, Jiang H, et al. Use of NTrap during ureteroscopic Holmiu& m : YAG laser lithotripsy of upper ureteral calculi. Minim Invasive Ther Allied Technol 2012; 21:78–82. Intraoperative stone migration is a major problem during Ho : YAG laser lithotripsy of upper ureteral calculi. A retroscpective study of 308 patients treated with ureteroscopy with and without NTrap was performed. Patients treated with NTrap had a higher intraoperative success of lithotripsy and a lower postoperative stone residual rate. They found longer operative times with the NTrap group, but the device was safely and effectively used during ureteroscopic procedures . 21. Ding H, Wang Z, Du W, et al. NTrap in prevention of stone migration & during ureteroscopic lithotripsy for proximal ureteral stones: a meta-analysis. J Endourol 2012; 26:130–134. The authors evaluated the effectiveness of NTrap in the prevention of stone migration during ureteroscopic lithotripsy for proximal ureteral stones. They evaluated two randomized controlled trials and one case–control trial including 456 patients. The NTrap group showed an advantage in stone free rates, lower stone migration and decreased auxiliary SWL. The authors recommend further higher quality randomized controlled trials. 22. Wosnitzer M, Xavier K, Gupta M. Novel use of a ureteroscopic stone entrapment device to prevent antegrade stone migration during percutaneous nephrolithotomy. J Endourol 2009; 23:203–207. 23. Olbert PJ, Keil C, Weber J, et al. Efficacy and safety of the Accordion stonetrapping device: in vitro results from an artificial ureterolithotripsy model. Urol Res 2010; 38:41–46.
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Urolithiasis 24. Pagnani CJ, El Akkad M, Bagley DH. Prevention of stone migration with the Accordion during endoscopic ureteral lithotripsy. J Endourol 2012; 26:484– 488. The purpose of the authors was to analyze the effect of the Accordion on stone migration and overall efficiency during lithotripsy. They prospectively analyzed 21 patients treated for 23 distal ureteral stones. The Accordion was randomly used in 11 of these 21 patients. Patients who were treated with the Accordion device experienced less retrograde migration during fragmentation (P ¼ 0.0064). 25. Wu JA, Ngo TC, Hagedorn JC, et al. The accordion antiretropulsive device && improves stone-free rates during ureteroscopic laser lithotripsy. J Endourol 2013; 27:438–441. The authors describe their experience with the Accordion device focusing on three main endpoints: operating time, fluoroscopy time and stone-free rates. They performed a retrospective review including 235 cases undergoing ureteroscopy for ureteral stones. Accordion device usage was not associated with a significant reduction in fluoroscopy time or operating time. However, the stone-free rate for the Accordion group was significantly higher compared to the non-Accordion group (84.2 vs. 53.6%, P ¼ 0.001). Therefore, the authors conclude that the Accordion device improved stone-free rates during ureteroscopic lithotripsy. 26. Mohseni MG, Arasteh S, Alizadeh F. Preventing retrograde stone displacement during pneumatic lithotripsy for ureteral calculi using lidocaine jelly. Urology 2006; 68:505–507. 27. Zehri AA, Ather MH, Siddiqui KM, et al. A randomized clinical trial of lidocaine jelly for prevention of inadvertent retrograde stone migration during pneumatic lithotripsy of ureteral stone. J Urol 2008; 180:966–968. &
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28. Molina WR, Pompeo A, Sehrt D, et al. Use of a polymeric gel to prevent retropulsion during intracorporeal lithotripsy. Actas Urol Esp 2013; 37:188–192. 29. Ahmed M, Pedro RN, Kieley S, et al. Systematic evaluation of ureteral occlusion devices: insertion, deployment, stone migration, and extraction. Urology 2009; 73:976–980. 30. Farahat YA, Elbahnasy AE, Elashry OM. A randomized prospective controlled study for assessment of different ureteral occlusion devices in prevention of stone migration during pneumatic lithotripsy. Urology 2011; 77:30–35. 31. Sarkissian C, Paz A, Zigman O, et al. Safety and efficacy of a novel ureteral && occlusion device. Urology 2012; 80:32–37. The authors evaluated the safety of a novel ureteral occlusion device and compared its performance with that of other devices and guidewires. They used an ex-vivo porcine model to evaluate urothelium trauma, stone migration and the ability use the device for stent placement. They also used an in-vitro model to compare insertion forces and maneuverability. The XenX prevented stone migration with minimal insertion forces and allowed for stent placement. The authors recommend further clinical studies. 32. Ursiny M, Eisner BH. Cost-effectiveness of antiretropulsion devices for && ureteroscopic lithotripsy. J Urol 2013; 189:1762–1766. The authors evaluated the cost-effectiveness of antiretropulsion devices used during ureteroscopic lithotripsy. A decision analysis model was constructed to compare the cost-effectiveness of ureteroscopic lithotripsy with vs. without an antiretropulsion device. The estimated costs of secondary procedures needed to treat retropulsed stones averaged $5840. The probability of retropulsion without an antiretropulsion device is 16.3%. It became cost-effective to use an antiretropulsion device at or above a 6.3% retropulsion rate.
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