New Technologies in Ultrasonic and Pneumatic Lithotripsy

Abstract

Background: Ultrasonic and pneumatic lithotripters are the gold standard for percutaneous nephrolithotripsy. The goal of this chapter is to help the reader become more familiar with the newer lithotripters and to critically select the best available lithotripsy device for each situation. Methods: A literature search was performed to identify all types of older and newer generation ultrasonic and ballistic lithotripters. Physics, characteristics, efficacy, and safety are discussed. Results: Newer dual lithotripters are more effective and allow disruption of stones both in the laboratory and clinical trials. CyberWandTM and Lithoclast Select lithotripters have similar stone disintegration rates in percutaneous nephrolithotripsy for stones >2 cm. UrerTron has a very rapid stone clearance rate, especially for hard stones, with no difference in stone clearance rates or need for secondary procedures. Lithoclast® Trilogy demonstrated superior stone clearance time compared to ShockPulse™ and Swiss Lithoclast® Select (Master) with high stone volume clearance rates in both standard and mini PCNL with a mean stone-free rate of 83%. However, more recent data have shown that neither lithotripsy device offers a clinically meaningful advantage over older generation devices. Conclusion: All the new lithotripsy devices have an excellent safety profile. They do not appear to be any more effective than the older generation devices. The advantages, disadvantages, and costs of each type of intracorporeal lithotripter must be considered when choosing a treatment modality for a particular case.

1. Introduction

Endourology is now the main player in the treatment of urinary stone disease. Intracorporeal lithotripsy is the cornerstone of modern endourology. It provides safe, effective, and reliable disintegration of urinary lithiasis. This advantage has translated into improved stone-free rates, reduced morbidity, and faster patient recovery. Technological advances in this field have led to the acceptance of endourology by urologists worldwide. Percutaneous nephrolithotripsy is generally considered the treatment of choice for stones 2 cm in diameter, staghorn calculi, or after failure of other endourologic procedures. It is a well-established procedure with stone-free rates exceeding 80%. Despite the high cure rates, there is a push for better results with an even faster procedure to reduce surgical time, especially for hard and large stones. In the last decade, there has been a trend toward combined lithotripsy procedures to overcome this handicap.

In this chapter, we first discuss the history, physics, and mechanics of ultrasonic and ballistic lithotripters. We then introduce the major players, from older to newer devices: the Swiss LithoClast® Select lithotripter, CyberWandTM, UreTron, ShockPulse SETM, and EMS Lithoclast® Trilogy. Key features, efficacy, and safety are discussed with a brief review of the current literature. The goal of this chapter is to help the reader become more familiar with the newer lithotripters and to critically select the best available lithotripsy device for the situation.

2. History of rigid lithotripsy

Ultrasonic vibration energy is more than 70 years old. The idea of using ultrasonic vibrational energy to disintegrate urinary calculi originated with Mulvaney, who tested the first model of lithotripsy in 1953 [1]. Successful in vivo ultrasonic lithotripsy was performed much later in 1970 by Terhorst [Terhorst], who used the energy to treat bladder stones [2]. Later in the 1970s, Marberger and Alken reported the first successful cases of percutaneous nephrolithotripsy (PCNL) with ultrasound in humans [3]. In 1993, pneumatic lithotripsy with the Swiss Lithoclast appeared in the field of intracorporeal lithotripsy [4]. A year later, a new device for ballistic lithotripsy with electrokinetic energy appeared on the market and the first series appeared in the international literature [5].

Since then, the innovation technology allowed the combination of both energies in the same device for better disintegration of the stones [6, 7].

3. Physics and properties of ultrasonic lithotripsy

Ultrasonic waves have an acoustic frequency that is inaudible to humans. Ultrasonic lithotripsy is based on the generation of ultrasound waves with a specific frequency of about 23–25 kHz. First, electric current is transmitted from an ultrasound generator to a handpiece transducer via a coaxial cable. The handpiece consists of piezoceramic elements and a longitudinal steel probe, which is adjusted at the distal tip of the probe. Activation of the device via a foot pedal causes excitation of the piezoceramic elements to produce acoustic waves at the specified frequency. The probe begins to vibrate in the longitudinal and transverse directions. When the probe comes into contact with a stone, the acoustic energy is transferred to the stone and the stone decomposes. The probe is usually hollow, and the back part of the handpiece is also connected to an aspirator to suck out small fragments and debris. If the probe is small in diameter, the suction cannot be used. Smaller probes are suitable for ureteric stone lithotripsy and larger ones for bladder and kidney stones.

Tissue changes are minimal and occur only after direct contact with the urothelium [8, 9]. Direct application of the ultrasound probe to the urothelial wall may cause epithelial abrasions and hemorrhagic edema of the lamina propria, which disappear after about a week [10]. A main advantage of ultrasonic lithotripsy is that it has a large safety margin even with a contact time of more than a few seconds with a minor force against the ureteral wall [11].

In PCNL, ultrasonic lithotripsy is performed by gently pressing the stone against the renal pelvis and rotating the probe against the stone to pulverize it by creating craters on it. This maneuver is repeated several times on the stone surface. The stone eventually weakens and disintegrates into smaller particles that are removed from the field by suction.

The probes are solid or hollow and vary in size from 2.5–5 Fr. They need a straight working channel. If they are twisted or bent at the insertion point of the working probe, ultrasonic energy is lost and heat is generated. Eventually, the probe becomes fatigued and may break at the junction with the handpiece.

Ultrasonic lithotripters successfully disintegrate soft stones, but hard stones, such as calcium oxalate monohydrate, brushite, and cystine are disintegrated less efficiently. Although the tip of the probe heats up during the procedure, this increase in temperature appears to be of limited clinical significance. The rise in temperature is limited to as low as 1.4°C, especially if adequate fluid irrigation in the surgical field of at least 30 ml/min is provided [12]. It provides excellent fragmentation and stone-free rates of 97% and 94%, respectively, with a low complication rate [13].

4. Physics and properties of pneumatic lithotripsy

The working principle of pneumatic lithotripsy is based on the momentum theorem. It is an analog of Newton’s cradle that allows the impact of one ball to remove another, and so on. A metal projectile was forced with a precision of one micrometer at high speed. When the projectile hits the probe installed in the handpiece, a shockwave is transmitted through the probe to the calculus [14].

In ballistic lithotripsy, energy is transmitted by the forward movement of a projectile, such as a jackhammer. The handpiece device receives energy from either an electromagnetic field or compressed air from the wall, and pneumatic lithotripters have a frequency of 12 Hz and receive compressed air at 3 atm. Electrokinetic lithotripters have a slightly higher frequency—15–30 Hz—and receive energy from the electromagnetic field. The different mechanical properties of the metal probe and stone lead to fast and effective lithotripsy. Proper fixation of the stone between the urothelium and probe eases the transmission of energy to the stone. Like ultrasound probes, ballistic probes also require rigid and straight working channels. Bowing of the probe results in considerable energy loss. Ballistic lithotripters can break hard stones regardless of their composition; however, they cannot produce fragments smaller than 4 mm [10]. This property makes ballistic lithotripsy useful for kidney and bladder stones and less useful for ureteric stones. The probe sizes are 0.8, 2.5, and 3.8 mm.

It has a good safety profile, with no thermal effects on the surrounding tissues and low maintenance costs [15]. Drawbacks include the risk of fragment migration, use of an offset semirigid ureteroscope, and the need for a basket or graspers to remove the fragments [13, 15]. In addition, in the presence of impacted stones in the case of lithotripsy in a narrow space, for example, a narrowed calyceal neck hemorrhage is less likely because of the mechanical impact of the road and repeated friction between the students, and because of the original collection system, this humoral loses the vision of the film.

The Cook StoneBreaker LMA™ is another type of portable ballistic lithotripter that does not require an external source of compressed air and uses prefilled cartridges filled with CO2. Each cartridge can deliver about 100 shocks. In a comparative study with Swiss Lithoclast, the device showed easier setup, use, and faster stone fragmentation [16]. A similar portable ballistic lithotripter is the EMS Swiss LithoBreaker, an electrokinetic lithotripter with a rechargeable battery. It delivers a single continuous shot at 3 Hz and a source capacity of up to 3.000 impulses. The probe sizes are 2.4–6 Fr. A single in vitro study showed decreased effectiveness of the device in a percutaneous model on a Bego Stone compared to a portable pneumatic device [17].

Regarding the biological effects on tissues, it seems that Lithoclast behaves in a manner similar to that of ultrasound lithotripters. Histologically, it induces minimal lesions consisting of a reduction in cell layers, epithelial detachment, and mild parietal edema [10].

The fragmentation and stone-free rates for both electrokinetic and pneumatic lithotripters are similar and are between 84 and 97.5% and 70–95%, respectively [13].

5. Operating principles of combination technologies in ultrasonic and pneumatic lithotripsy

The combination of both energies has the advantages of both energies. On the one hand, constant emission of ultrasonic energy allows for fine fragmentation and dusting of stones, whereas intermittent ballistic shocks allow for the powerful and coarse fragmentation of large and hard stones. Thus, it could be assumed that initially, the hard parts of a stone break up with the ballistic part to bigger fragments, and as the lithotripsy advances, the ultrasonic component leads to pulverization of the small and short fragments of the stone. Simultaneous suction allows continuous removal of debris and even larger stone fragments, depending on the size of the probe. All combinations of older and newer lithotripters are presented in Table 1.

Type	Probe		Energy	Company
The Swiss LithoClast® Select Lithotripter	two probes	reusable	ultrasonic and pneumatic energy	EMS S.A., Switzerland/Boston Scientific, USA
CyberWandTM	two probes	reusable	ultrasonic waves in two different frequencies	Olympus, Tokyo, Japan
UreTron	one probe	reusable	ultrasonic frequency control technology	Richard Wolf
ShockPulse SETM	one probe	reusable/single use	constant ultrasonic wave energy lithotripter with intermittent shock wave (ballistic/mechanical) energy	Olympus
Swiss Lithoclast® Trilogy	one probe	single use	ultrasound and electromagnetic ballistic energy	EMS S.A., Switzerland

Table 1.

Newer generation and combination lithotripers.

6. Types of new lithotripters

6.1 Swiss LithoClast® select lithotripter (EMS S.A., Switzerland/Boston Scientific, USA)

The Swiss LithoClast® Select Lithotripter device is a two-probe dual-modality. This device also allows simultaneous transmission of ultrasonic and pneumatic energy to the stones when it is used with a special handpiece of the Vario device. Each type of energy can also be used separately for each of the two probes. It also allows for the same session to switch from only ultrasonic energy to both modes of energy. It also allows suction. Occasionally, malfunction of the device can occur with clogging of the probe. The main advantage of the combination of pneumatic and ultrasonic lithotripters is that they can disintegrate and clear stones at a more effective and rapid rate with slightly improved stone-free rates [9, 18, 19].

6.2 CyberWand™ (Olympus, Tokyo, Japan)

CyberWand™ is an electromechanical device that is capable of fragmenting and aspirating calculi. The handpiece has an ultrasonic transducer containing a piezoelectric element, which is driven by a generator operating at 20–22 kHz. This is a dual-ultrasonic lithotripter. It has two separate ultrasonic probes that vibrate at two different frequencies, high and low. The outer probe, 3.75 mm in diameter, vibrates at one kHz and is designed for breaking smaller stones. The inner probe is designed for larger stones with a 2.77 mm and vibrates at 21 kHz with a 2.1 mm hollow inner lumen. Its efficacy is thought to be due to the synergistic effect of the two probes vibrating at different rates. The outer probe is approximately 1 mm shorter than the inner probe and is thought to have some ballistic effect on the stones.

In a comparative study, CyberWandTM and Lithoclast Select lithotripters had similar stone clearance rates in PCNL for stones >2 cm. The safety and efficacy of these devices were comparable [20]. However, measurement of occupational noise exposure during endourologic procedures with the CyberWandTM was noted to be significantly louder than other lithotripsy devices [21].

6.3 UreTron (Richard Wolf)

It is an electromechanical device that consists of a generator, handpiece, and probes. UreTron is a single-probe lithotripsy device with a frequency of vibration—21–22 kHz. It was approved by the Food and Drug Administration (FDA) in 2012. The handpiece is an ultrasonic transducer with piezoelectric ceramic elements. Although it is not a combined lithotripsy device, it has a new technology and merits special attention. The unique design of the UreTron system focuses more on sonic energy on the probe. It uses a unique micro-controller-based algorithm combined with an advanced physical component design, which allows this unique transmission capability to be used with flexible, semiflexible, and rigid probes. The probes had a 3.1-mm outer diameter and 2.5-mm inner diameter, although a 3.5-mm probe is available as well. The foot pedal has a hard stone and soft stone mode, each offering unique pulsing patterns meant to optimize fragmentation. Finally, fragments are sucked out. The system can aspirate stones simultaneously while operating at full power.

It has a very fast clearance stone rate (52 mm³/min), especially for hard stones, with no differences in stone-free rates or need for secondary procedures. The malfunction rate was 16%, which is similar to that of other devices. Most of the issues were temporary and resolved. The most common issue was clogging of the device by stone debris, which was easily resolved by flushing. In addition, probe breakage can occur, which can easily be replaced by a new one [22].

6.4 ShockPulse SE™ (Olympus, Tokyo, Japan)

ShockPulse is a lithotripsy system that is the next generation of CyberWand. It was approved by the Food and Drug Administration (FDA) in 2014. This is a dual-action system for lithotripsy. It is composed of three elements: generator, shock wave transducer, and probe. The generator provides constant ultrasonic wave energy at approximately 21 kHz, along with intermittent shockwave energy at a high rate of 300 Hz. The shockwave probe has two buttons, one for high-power lithotripsy and one for standard-power lithotripsy. In addition, the handpiece transducer incorporates an adjustable suction control wheel that can rotate by approximately 20° from off to full flow.

ShockPulse technology works owing to its unique probe design. It has a return spring anteriorly for the creation of a high-energy shockwave and a back-free part that oscillates back and forth owing to vibration that sends propulsions at 300 Hz.

Probes of various sizes allow for standard percutaneous nephrolithotripsy, mini PCNL, URS lithotripsy, and bladder lithotripsy. 3.76 mm and 3.4 mm for PCNL and bladder, respectively. Mini PCNL is feasible with a 1.83 mm probe and URS lithotripsy with 1.50 and 0.95 mm probes. The latter does not allow suction. In an in vitro study, ShockPulse™ had a faster fragmentation and evacuation rate than LUS-II and Swiss LithoClast® Master [23]. The probes also had larger diameters, which could explain the faster evacuation rate [24].

6.5 Swiss Lithoclast® trilogy

The Swiss Lithoclast® Trilogy is the first device to combine an electromagnetic impactor with ultrasonic energy and suction, all in one probe. It was approved by the FDA in 2018. The trilogy consists of a pistol-grip handpiece with a disposable probe and a console used to set the treatment parameters and generate treatment energy. It can deliver ultrasonic and electromagnetic ballistic energy up to 12 Hz simultaneously or independently and has a suction function. It has a switch control pedal for both suction and energy control. Disposable probes range from 1.1 mm up to 3.9 mm (3.3–11.7 Fr). Disadvantages include the 1200 g weight of the handpiece which makes it less user friendly, leading to low physician satisfaction. It has an excellent safety profile with a downward displacement of the probe tip of 0.041 mm and a superimposed impactor-generated downward movement of 0.25 mm at 6–12 Hz [25, 26]. In vitro, the Lithoclast® Trilogy showed a superior stone clearance time compared to ShockPulse™ and Swiss Lithoclast® Select (Master) [25]. It is highly effective in both standard and mini PCNL, for which the mean stone volume clearance rates were 590.7 and 370.5 mm³/min, respectively [26]. In a prospective nonrandomized study from ten European centers, the mean stone clearance was 65.55 mm³/min or 945 mm³/min calculated on 3D volume with an 83% stone-free rate on fluoroscopy screening at the end of the procedure with a 5% probe breakage [27]. In a systematic review study, Swiss Lithoclast Trilogy and ShockPulse SE were found to be equally effective, safe, and versatile for standard and mini PCNL [28]. However, newer data have shown that both lithotripsy devices do not confer any clinically meaningful advantage over older generation devices [29].

7. Conclusion

Older ballistic and ultrasonic devices are still viable with proven, time-tested efficacy, and safety over many years. New technological advances, including single-probe and dual-modality lithotripters using a combination of ultrasonic and ballistic characteristics, have excellent safety profiles. Although they were initially promising, they do not appear to be more effective than older generation devices. The advantages and disadvantages of each type of intracorporeal lithotripter must be considered when choosing a treatment modality for a given case.

Conflict of interest

The authors declare no conflict of interest.