In Vitro Comparison of a Novel Single Probe Dual-Energy Lithotripter to Current Devices

Abstract

Purpose:

The LithoClast Trilogy is a novel single probe, dual-energy lithotripter with ultrasonic (US) vibration and electromagnetic impact forces. ShockPulse and LithoClast Select are existing lithotripters that also use a combination of US and mechanical impact energies. We compared the efficacy and tip motion of these devices in an in vitro setting.

Materials and Methods:

Begostones, in the ratio 15:3, were used in all trials. Test groups were Trilogy, ShockPulse, Select ultrasound (US) only, and Select ultrasound with pneumatic (USP). For clearance testing, a single investigator facile with each lithotripter fragmented 10 stones per device. For drill testing, a hands-free apparatus with a submerged balance was used to apply 1 or 2 lbs of pressure on a stone in contact with the device tip. High-speed photography was used to assess Trilogy and ShockPulse's probe tip motion.

Results:

Select-USP was slowest and Trilogy fastest on clearance testing (p < 0.01). On 1 lbs drill testing, Select-US was slowest (p = 0.001). At 2 lbs, ShockPulse was faster than Select US (p = 0.027), but did not significantly outpace Trilogy nor Select-USP. At either weight, there was no significant difference between Trilogy and ShockPulse. During its US function, Trilogy's maximum downward tip displacement was 0.041 mm relative to 0.0025 mm with ShockPulse. Trilogy had 0.25 mm of maximum downward displacement during its impactor function while ShockPulse had 0.01 mm.

Conclusions:

Single probe dual-energy devices, such as Trilogy and ShockPulse, represent the next generation of lithotripters. Trilogy more efficiently cleared stone than currently available devices, which could be explained by its larger probe diameter and greater downward tip displacement during both US and impactor functions.

Introduction

Historically, percutaneous nephrolithotomy was performed with single-energy ultrasonic (US) and pneumatic lithotripters. Yet, US-only lithotrites are limited in their ability to adequately fragment hard stones.¹ Pneumatic-only devices easily fragment hard stones, but have no suction capability to clear those fragments. The subsequent development of dual-energy lithotrites has shown that combined US and pneumatic lithotripters achieve faster fragmentation and complete disintegration times than their single-energy counterparts.¹ Two currently available dual-energy lithotripters are the LithoClast Select^™ (ElectroMedical Systems, Switzerland) and the Olympus ShockPulse Stone Eliminator^™ (Olympus, Japan). The ShockPulse is a single probe dual-energy device and is the newest lithotripter on the market in the United States. So far in vitro work has shown the ShockPulse to be at least equivalent if not superior to other available devices.²

The LithoClast Trilogy (ElectroMedical Systems) is a novel single probe dual-energy device, which offers individually modifiable US and mechanical fragmentation with variable suction. In a benchtop setting, we evaluated the Trilogy's ability to fragment and clear stone relative to the ShockPulse and the Select. Additionally, probe tip dynamics for the ShockPulse and Trilogy were evaluated with high-speed photography.

Materials and Methods

Instruments

The Trilogy's two energies are activated together by depressing a single foot pedal. The impactor activates at up to 12 Hz and the frequency of its US function is not published. The Trilogy's functional trifecta (ultrasound, impactor, and suction) are individually modifiable with each controlled by a digital interface on the generator (Fig. 1A). As per manufacturer's guidelines, the Trilogy's impactor was set at 80% and ultrasound at 100%. The Trilogy's suction was set at 40%—equivalent to 300 mL/minute. For standardization purposes, the Trilogy's suction generator was used at this rate for all devices. A probe with an external diameter of 3.9 mm was used for all tests of the Trilogy.

FIG. 1.

(A) Trilogy generator that allows the following to be individually modified: ultrasonic power, suction, impactor power, and impactor frequency. Handpiece and probe lie on top of the generator. (B) Hand-held stone clearance set-up. (C) Hands-free fixed weight drill test with underwater balance and counterweight applying 1 or 2 lbs of pressure to the stone–probe interface. Lithotripter handpieces were fixed to a ringstand by a rubber-tipped claw.

The ShockPulse has a single probe that delivers both US and mechanical impactor functions provided by piezoelectric handpiece elements that produce US energy at 21 kHz with intermittent ballistic shockwaves delivered at 300 Hz.² For the ShockPulse, tests were performed in high power mode. We utilized the largest available probe with an external diameter of 3.76 mm and, as stated above, suction was maintained at 300 mL/minute utilizing the built-in suction of the Trilogy.

The Select is a first-generation dual probe dual-energy device that uses US vibration at 23.2–26.4 kHz³, and a pneumatically driven, independent impactor rod to fragment stone. The probes can be individually activated or used in concert by pressing both foot pedals. For the purposes of this study, we evaluated the Select at maximum US and pneumatic power settings in two scenarios: ultrasound only (Select-US) and ultrasound with continuous pneumatic (Select-USP) firing. We used the largest US probe available with an external diameter of 3.8 mm and a 1 mm pneumatic probe operating at 12 Hz. The pneumatic impactor rod was not in place during the US-only test runs. Once again, the Trilogy suction was used for this device as well.

Clearance testing

One cubic centimeter Begostones with hardness mimicking calcium oxalate monohydrate stones (15:3) were used for all test runs.⁴ A single stone was placed in a hemispherical silicone support in a water bath (Fig. 1B). Test groups included the Trilogy, ShockPulse, Select-US, and Select-USP. By hand, a single urologist familiar with all devices used each lithotripter to completely fragment and clear a Begostone with 300 mL/minute of constant suction. Filtered suction outflow was directed back into the water bath to maintain the water level. Time until complete evacuation of the Begostone was recorded. A total of 10 runs were completed for each device. The probe, handpiece, and suction tubing were cleared of Begostone fragments between runs to avoid obstruction.

Fixed-weight drill test

Each lithotripter was securely fixed to a hands-free apparatus that allowed for the probe tip–stone interface to occur underwater. A 1.5 cm³ Begostone (15:3) was placed on one end of an underwater balance with either 1 or 2 lbs of counter pressure on the opposite side (Fig. 1C). The lithotripter probe was positioned in contact with and perpendicular to the Begostone surface. Lithotripsy and suction were activated until the stone was completely drilled through. Ten trials were performed per device with five at each fixed weight. The probe, handpiece, and suction tubing were cleared of fragments between runs.

Tip dynamics

Given the fundamental difference in fragmentation modalities and tip design, we compared tip dynamics for only the single probe dual-energy devices—Trilogy and ShockPulse.

The same hands-free apparatus used for fixed-weight drilling was employed to secure each lithotripter. The devices were not submerged in water to avoid distortion of the high-speed images. From a fixed distance, each device was activated for one second and images acquired at one frame per 4-5 μsecond using a high-speed 14-bit CMOS camera (1 μsecond exposure; Vision Research, Inc., NJ). Images were then uploaded into MATLAB (MathWorks, MA) and tip excursion in millimeters plotted on curves.

Statistical methods

Mean times clearance and drill times were calculated for each lithotripter. One-way analysis of variance (ANOVA) was performed for clearance and drill times between the four devices. Significance was set at p < 0.05 and analyses performed with SPSS v25 (IBM, NY).

Results

Clearance testing

The LithoClast Trilogy had the fastest mean clearance time of 23.79 seconds. This was followed by the ShockPulse (46.04 seconds), Select-US (54.86 seconds), and Select-USP (102.48 seconds). One-way ANOVA revealed a difference between the four groups (p = 0.001). Tukey's HSD showed that the Trilogy was significantly faster than all other devices (p < 0.01). There was no statistical difference in clearance times between the ShockPulse and Select-US (p = 0.52). All devices were faster than the Select-USP (p < 0.01) (Fig. 2A).

FIG. 2.

(A) Mean hand-held stone clearance times. *Different from all other devices (p < 0.01). Bars show one standard deviation. (B) Mean drill times with 1 lb weight. *Different from all other devices (p = 0.001). Bars show one standard deviation. (C) Mean drill times with 2 lbs weight. *Only different from each other (p = 0.027). Bars show one standard deviation.

Drill testing

In both the 1 and 2 lbs groups, there were no statistically significant differences between any of the dual-energy devices: the Select-USP, Trilogy, and the ShockPulse. One-way ANOVA was significant for the 1 and 2 lbs runs (p < 0.0001 and p = 0.035, respectively). Tukey's HSD for the 1 lb group showed the Select-US mean drill time (76.49 seconds) to be significantly slower than all other devices with times from 10.42 to 15.72 seconds (p = 0.001). There was no significant difference among the other lithotripters (Fig. 2B). In the 2 lbs group, the ShockPulse mean time (9.41 seconds) was significantly faster than the Select-US (25.19 seconds) (p = 0.027). However, there was no statistically significant difference in drill time between the ShockPulse and the Trilogy (20.49 seconds, p = 0.16) nor the Select-USP (16.30 seconds, p = 0.52) (Fig. 2C). Overall, in both fixed-weight groups, there was no statistically significant difference between any of the dual-energy devices: the Select-USP, Trilogy, and the ShockPulse.

Tip dynamics

The Trilogy's US probe tip motion is shown in Figure 3. The Trilogy was noted to have up to 0.041 mm of downward displacement relative to 0.0025 mm seen with the ShockPulse (Fig. 4). Individual impactor movements were identified as larger, more infrequent downward movements corresponding to advertised rates for each device, ShockPulse at 300 Hz and Trilogy at 12 Hz. The Trilogy had 0.25 mm of downward tip displacement (Fig. 5) when the impactor was activated, whereas the ShockPulse had 0.01 mm (Fig. 4).

FIG. 3.

Trilogy ultrasonic tip displacement. During baseline ultrasonic motion maximum downward displacement is 0.041 mm.

FIG. 4.

ShockPulse ultrasonic and impactor tip displacement. During baseline ultrasonic motion maximum downward displacement is 0.0025 mm. During impactor activation, maximum downward probe tip displacement of 0.01 mm. Phases of impactor action: primary descent—triangles; recoil—arrows; secondary descent—stars. Baseline ultrasonic function—square.

FIG. 5.

Trilogy impactor tip displacement. Maximum downward probe tip displacement of 0.25 mm. Phases of impactor action: primary descent—triangles; recoil—arrows; secondary descent—stars. Baseline ultrasonic function—square.

Each device's impactor demonstrates three phases: primary descent, recoil, and secondary descent. However, the Trilogy moves greater distances during both descents and recoil. After primary descent, the Trilogy recoils from the nadir up to 0.8 mm in the opposite direction. From this recoiled position starts the secondary descent wherein the downward displacement nadir is reached again. The secondary descent differs from the primary as it has bifid peaks rather than a single plateau. After secondary descent, the probe tip returns to its baseline US position. This differs from the ShockPulse as its impactor function has a primary descent that nadirs at only 0.0025 mm from its baseline position. From there, it recoils 0.013–0.015 mm in the opposite direction. Then, it starts the secondary descent that meets the downward displacement nadir of 0.0025 mm from baseline.

Discussion

We present the first evaluation of the latest single probe dual-energy lithotripter—the novel LithoClast Trilogy.

The release of the LithoClast Master/Ultra in 2001⁵—later to be redesigned and marketed in the United States as the LithoClast Select—represented a paradigm shift away from single modality US and pneumatic devices. The ability to have effective US fragmentation with suction in addition to a pneumatic impactor was a welcome addition to the endourologist's repertoire. It allowed for more efficient stone fragmentation^6,7 and removal of both hard and soft stone without the burden of exchanging single energy lithotripters. However, problems did remain; when the pneumatic probe is in place the Select is relatively large, heavy, and its probe-within-a-probe design is susceptible to clogging. Additionally, the US probe is prone to overheating and has been recommended to be used at 40%–70% power.⁷ It has taken until the recent release of the ShockPulse and upcoming Trilogy for there to be another major stride in lithotripter design and functionality.

These single probe dual-energy lithotripters blend efficacious US fragmentation with forceful impactor functionality while preserving a relatively large probe lumen for suctioning of fragments. This design allows for simultaneous fragmentation and clearance of both hard and soft stones. In itself, this significant technological advance warrants further investigation.

In a similar manner to previous benchtop evaluations for percutaneous lithotripters we measured fixed-weight drilling^2,8
–10 and time to complete Begostone clearance.² Hand-held clearance testing represents the most clinically similar in vitro assessment of a lithotripter's ability to fragment and evacuate stone. A direct comparison of hand-held clearance times between our study and the work previously done by Chew et al.² is challenging given differences in the units of measurement and type of stone phantom utilized. However, we can infer that our results are relatively similar. Their group noted the ShockPulse to fragment and clear hard stone phantom (Ultracal-30) ∼20% faster than the Select-US on hand-held clearance testing, but the difference was on the edge of statistical significance (p = 0.046).² In our clearance tests, the Trilogy was robustly superior with a mean clearance time nearly twice as fast as its contemporary, the ShockPulse, and over four times more efficient than the Select-USP with p < 0.01 in all cases.

While there was no difference between the ShockPulse and the Select-US, the ShockPulse was superior to the dual-energy Select-USP. In fact, the Select-USP was slower than all devices to statistical significance. At first, this finding can seem counterintuitive. We would expect that dual-energy utilization should clear a hard stone phantom faster than the Select-US alone. However, we offer two potential explanations.

First, the Select-USP's pneumatic probe extends beyond the perpendicular plane of the Select's US probe which evacuates the stone fragments. The extended pneumatic probe may push stone pieces away from additional US fragmentation and suction. The Select-USP's relative inefficiency was likely not seen on drill testing as the direction of fragmentation was linear. As such, the fragments were trapped and captive to additional fragmentation and suction. Second, the Select-USP's probe-within-a-probe design hinders fragment evacuation by limiting the available probe diameter for suction of fragments.

There are scenarios when using a lithotripter to drill into a stone is clinically advantageous. The opposite is also true, as drilling through a stone to the point where the probe tip is not visible is potentially dangerous. Given the clinical applicability of a lithotripter's drilling action and to provide a test free from operator bias we performed fixed-weight drill tests. These trials did not identify a superior device to statistical significance. These results should be contextualized in that the drill test offers a limited evaluation as it obviates a lithotripter's dynamic rotational¹⁰ and lateral movements commonly employed in a clinical setting. However, from the drill tests we can conclude that some degree of pneumatic or impactor functionality alongside US energy can lead to more efficient stone fragmentation as all dual-energy devices were found to be no different from one another, but superior to the Select-US.

To our knowledge, we have performed the first evaluation of percutaneous lithotripter probe tip dynamics with a high-speed camera. Understanding the intricacies of the novel single probe dual-energy lithotripters' tip displacement does not just satisfy intellectual curiosity; it is also an important safety consideration. We found that the baseline US oscillations have minimal probe tip excursion, 0.041 mm for the Trilogy and 0.0025 mm for the ShockPulse. The impactor functions for the Trilogy and ShockPulse have a larger downward tip displacement of 0.25 and 0.01 mm, respectively. These are small movements relative to pneumatic lithotripsy devices, such as the StoneBreaker^™ (Cook Medical, Bloomington, IN), which have a rod that extends 1–3.5 mm beyond their flush probe tip.¹¹ Additionally, Santa-Cruz and coworkers¹² activated a pneumatic lithotripter with a 1–3.5 mm tip displacement while at a right angle flush with porcine ureteral urothelium continuously for 6 minutes without perforation. Therefore, it is safe to extrapolate that the relatively small impactor movements of the Trilogy (0.25 mm) and ShockPulse (0.01 mm) are less likely to cause tissue injury than their pneumatic predecessors.

Overall, the next-generation percutaneous lithotripters—ShockPulse and Trilogy—were shown to have a safe amount of tip displacement. Additionally, their benchtop fragmentation times are as good as or better than the previous generation LithoClast Select. In the hand-held clearance test, the Trilogy performed better than all other devices, including its contemporary, the ShockPulse. This finding could in part be attributed to the Trilogy US probe tip displacement, which was over 16 times greater than the ShockPulse. Additionally, the Trilogy's impactor function had a much greater downward displacement distance. Lastly, the Trilogy's relatively large probe tip diameter (3.9 mm) likely also contributed to its superior stone phantom clearance.

Our study has a few notable limitations. First, it is an in vitro study wherein clinical conclusions can only be indirectly inferred. To mitigate this drawback, we performed a hand-held clearance test, which mimics clinical lithotripter application. Additionally, given that all tests were performed by a single urologist it was impossible for them to be blinded during testing. To assuage operator bias we performed the fixed-weight drill tests as discussed. Another limitation is that we evaluated the devices with only hard Begostones approximating the density of calcium oxalate monohydrate stones. While these devices may perform differently with softer stones, each lithotripter utilizes high-frequency continuous US energy, which has been documented to efficiently fragment and clear soft stones.¹³ Lastly, we continuously activated the Select-USP's pneumatic probe during the test to decrease variability that could be introduced by intermittent pneumatic use. In our experience, this technique is contrary to most urologists' clinical practice, where they use the pneumatic feature intermittently to fragment only hard portions of stone. This practice may have artificially decreased the efficacy of the Select-USP in the clearance testing.

Conclusions

In an in vitro setting, the novel single probe dual-energy Trilogy was more efficient than currently available devices for stone clearance. Drill testing revealed no difference between the Trilogy, ShockPulse, and the LithoClast Select-USP. High-speed imaging demonstrated the single probe dual-energy ShockPulse and Trilogy to have less probe tip excursion during their impactor function than older percussive devices previously deemed safe and effective. The Trilogy's relatively large probe tip diameter and increased US and impactor tip displacement may explain its superior stone clearance. Comparative clinical studies are needed in the future to truly evaluate the improvements seen in this analysis.

Footnotes

Acknowledgments

The authors would like to acknowledge the technical support provided by Chen Yang and Jingqiu Li.

Author Disclosure Statement

Drs. G.M.P. and M.E.L. serve as consultants for Boston Scientific. Dr. B.H.C. is a consultant to Boston Scientific, Cook Medical, and Olympus Medical. None of the other authors has any relevant disclosures.

Abbreviations Used

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