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Adv Chronic Kidney Dis. 2009 January ; 16(1): 60–64. doi:10.1053/j.ackd.2008.10.008.

Surgical Management of Stones: New Technology

Brian R. Matlaga and James E. Lingeman
James Buchanan Brady Urological Institute, Johns Hopkins Medical Institutions, Baltimore, MD;
and Methodist Hospital Institute for Kidney Stone Disease and Indiana University School of
Medicine, Indianapolis, IN

Abstract
In recent years, the surgical treatment of kidney stone disease has undergone tremendous
advances, many of which were possible only as a result of improvements in surgical technology.
Rigid intracorporeal lithotrites, the mainstay of percutaneous nephrolithotomy, are now available
as combination ultrasonic and ballistic devices. These combination devices have been reported to
clear a stone burden with much greater efficiency than devices that operate by either ultrasonic or
ballistic energy alone. The laser is the most commonly used flexible lithotrite; advances in laser
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lithotripsy have led to improvements in the currently utilized Holmium laser platform, as well as
the development of novel laser platforms such as Thulium and Erbium devices. Our understanding
of shock wave lithotripsy (SWL)has been improved over recent years as a consequence of basic
science investigations. It is now recognized that there are certain maneuvers with SWL that the
treating physician can do that will increase the likelihood of a successful outcome while
minimizing the likelihood of adverse treatment-related events.

Index Words
Shockwave lithotripsy; Lithotrite; Laser; Holmium; Thulium; Erbium

Introduction
The surgical treatment of patients with kidney stone disease is greatly dependent on surgical
technology, and as technology advances, procedures and techniques that were at one time
inconceivable become possible and even commonplace. No case shows this progression
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better than shockwave lithotripsy(SWL); patients who once required open surgical stone
removal could, after the introduction of SWL, be treated in a completely noninvasive
fashion. Just over 2 decades after its introduction, SWL has become the most commonly
applied treatment for patients with upper urinary tract stone disease.1

Although in recent years we have not witnessed the introduction of a paradigm-shifting

technology such as SWL, more subtle advances have, nonetheless, occurred. Herein, we
review recent advances in surgical technology used in the treatment of patients suffering
from stone disease.

© 2009 by the National Kidney Foundation, Inc. All rights reserved.

Address correspondence to Brian R. Matlaga, MD, MPH, Johns Hopkins Medical Institutions, Johns Hopkins Bay view Medical
Center, The Brady Urological Institute, 600 North Wolfe Street, Baltimore, MD 21209, bmatlag1@jhmi.edu.
 Matlaga and Lingeman Page 2

Intracorporeal Lithotripsy
Ultrasonic and Ballistic
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Intracorporeal lithotripsy is one of the integral elements of percutaneous stone treatment. In

general, the majority of commercially available intracorporeal lithotripters are ultrasonic
devices, which can efficiently fragment and remove the majority of stone types. However,
there are certain stones, such as those composed of cystine or calcium oxalate monohydrate,
that are less efficiently fragmented and removed with ultrasonic technology. For such
stones, pneumatic lithotripters are often used for fragmentation because these devices
readily break stones of any composition. However, the chief disadvantage of pneumatic
lithotripters is their inability to concurrently evacuate stone debris while fragmenting the
stone. Rather, manual fragment removal is necessary when using a pneumatic lithotrite, an
often time-consuming process.

Several manufacturers have introduced combined ultrasonic and pneumatic devices that aim
to combine the superior fragmentation ability of the pneumatic component with the ability of
the ultrasonic modality to simultaneously evacuate stone fragments. The first combination
device brought to the clinical market was the Lithoclast Ultra (Boston Scientific, Natick,
MA), which relied on a combination hand piece (actually, 2 separate hand pieces connected
together) to join the ultrasonic and pneumatic components. The first portion of the
combination hand piece was a traditionally designed pneumatic handle, with a smaller
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diameter solid probe. The ultrasonic handle, driven by a standard piezoelectric mechanism,
was modified to allow the coaxial insertion of the pneumatic probe. Each modality could be
activated separately or in unison; when operated in unison, the ballistic fragmentation of the
stone is accomplished with the pneumatic component, and the ultrasonic component then
removes the resulting debris.

A rigorous and impartial evaluation of intracorporeal lithotripters is a subject of importance

to urologists because each device may have certain unique properties that make it more
suitable for particular applications. Manufacturer’s claims may contain elements of bias,
making it difficult for the urologist to ascertain which device may be most suitable for their
practice. Therefore, a number of investigators have devised testing methods to compare
intracorporeal lithotrites. Liatsikoset al2 first reported an in vitro testing system designed to
measure the efficiency of ultrasonic lithotrites in which stone phantoms were fragmented in
a nephroscope-guided manner. The inherent weakness in this study design was that stone
fragmentation was directed by hand, which could introduce significant operator bias. Haupt
and Haupt3 subsequently reported an in vitro system that relied on an elaborate weight and
fulcrum to bring a stone phantom into contact with the probe tip at a constant force.
Although operator bias was no longer present, this system was complex and cumbersome,
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making replication challenging. Kuo et al4 have presented a novel and simple hands-free
testing system in which the ultrasonic hand pieces were secured upright and the stone
phantom placed into contact with the probe by a weight mechanism(Fig 1). This design
system was first used to test the efficiency of pure ultrasonic lithotrites and measured the
time it took for the probe to penetrate the stone phantom. In this study, the Olympus LUS-2
(Olympus, Melville, NY) produced the fastest overall stone penetration time.

After the introduction of the combination ultrasonic and pneumatic devices, the same testing
apparatus previously used by Kuo etal5 to evaluate the ultrasonic devices was used to
evaluate the Lithoclast Ultra. Because of the wide variety of ultrasonic power and pneumatic
frequency settings available, the testing apparatus was used to assess the efficiency of
various setting combinations. The endpoint was stone penetration time, and the fastest stone
penetration times were achieved at settings of 100% ultrasonic power and 12-Hz pneumatic
frequency. Pietrow et al6 have evaluated the efficiency of the Lithoclast Ultra combination

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device in a clinical setting, performing a prospective, randomized trial comparing the

combination device to standard ultrasonic lithotrites in patients undergoing percutaneous
nephrolithotomy. The stone clearance times were significantly better for the combination
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device than for the convention alultrasonic lithotripters.

The Cyber wand (Gyrus ACMI, Southborough, MA) is an intracorporeal lithotripter that
relies on a dual ultrasonic probe design that incorporates coaxial high-frequency and low-
frequency probes. The dual-probe design creates a synergistic effect that enables efficient
stone fragmentation while still allowing the suction evacuation of small fragments just as
other ultrasonic devices do. Kim et al7 used the aforementioned hands-free testing design
previously described by Kuo et al and found that the stone penetration time for the
Cyberwand was almost twice as rapid as it was for the Lithoclast Ultra.

Laser
Any stone within the urinary tract may be treated with the holmium: yttrium aluminum
garnet. Laser lithotripsy is sensitive to stone size, and for large stone burdens, the
procedure’s efficacy can be markedly reduced. When the stone burden increases beyond 1.5
cm, the likelihood of achieving a stone-free outcome is reduced, and such patients maybe
best approached in a percutaneous fashion using a rigid lithotrite. The only true
contraindication to holmium laser lithotripsy of urinary calculi is the presence of untreated
infection because life-threatening sepsis may result. Otherwise, there are no other specific
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contraindications to holmium laser lithotripsy. Indeed, even patients receiving

anticoagulation therapy have been reported to have successfully undergone holmium laser
treatment of urinary calculi.

The holmium laser is one of the safest intracorporeal lithotrites available for stone
fragmentation. The most significant adverse event is injury of the urothelial tissue adjacent
to the treated stone. The depth of tissue penetration of the holmium laser is 0.5 to 1.0 mm, so
in most cases such injuries may be managed conservatively, although a ureteral stricture
may be a long-term consequence of such an event. The holmium laser does produce a weak
shockwave, so in some cases stone fragments can be retro pulsed and migrate away from the
endoscope, which may increase the complexity of the procedure. Eye protection is required
for operators of the holmium laser, although at the energy levels used for the fragmentation
of calculi, the operator’s cornea would be damaged only if it was positioned at less than 10
cm from the laser fiber.

The field of laser lithotripsy is advancing in 2 different directions: improvements to the

existing holmium laser platform and the development of novel laser platforms. The most
significant improvement in holmium laser lithotripsy will likely come from improved
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delivery fibers. At present, the smallest fiber in wide spread use, the 200-μ fiber, impedes
the deflection of a flexible ureteroscope by up to 20°. As smaller laser fibers, such as those
of 150-μm diameter and smaller, are produced, it is likely that this effect on endoscope
deflection will be further reduced. The fracture of a laser fiber inside of an endoscope can
result in a catastrophic failure of the scope because when this occurs the fiber optic bundles
that transmit images and light are generally destroyed. Future efforts toward maximizing
fiber durability may reduce these events.

The erbium: yttrium aluminum garnet laser has recently been tested for the fragmentation of
urinary calculi; the high-temperature water absorption coefficient at the erbium laser
wavelength of 2.94 μ is about 30 times higher than that of the holmium laser wavelength at
2.12μ, which has translated to a 2-to 3-fold increase in efficiency for fragmenting urinary
stones in an in vitro setting.8 There are several limitations of the erbium laser that prevent its
immediate use for clinical applications in urology. The erbium wavelength cannot be

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transmitted through standard available silica fibers; specialty mid-infrared fibers are needed,
and these fibers are typically less flexible, more expensive, and less biocompatible than
silica fibers.
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Recent advances in fiber laser technology have resulted in the commercial availability of the
thulium laser, which has several potential advantages over other solid-state lasers such as the
holmium. The thulium fiber laser wavelength is tunable, and, when operated in the pulsed
mode, it is capable of fragmenting urinary calculi.9 In addition, the thulium fiber laser-beam
diameter is only 18 μ, allowing easy coupling of the laser radiation into small-core optical
fibers. Such diminutive fibers have a great potential use when coupled with flexible
endoscopes in demanding applications, such as access to the lower pole of the kidney for
lithotripsy.

SWL
SWL revolutionized the field of stone disease. Although it was initially thought that shock
wave energy would pass harmlessly through the kidney, it is now well documented that
renal injury occurs as a side effect of SWL; detailed morphologic analyses of porcine
kidneys treated with a clinical dose of shock waves have shown that shockwave energy
induces a hemorrhagic lesion in the renal vasculature. The volume of the hemorrhagiclesion
is dose dependent, and, as the number of shocks and the power settings of the lithotripter are
increased, the lesion size will similarly increase.10,11
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Although efforts are underway to develop new lithotripter technologies that will ultimately
make SWL safer and more effective, at present, a fundamental question remains open; how
can we maximize stone fragmentation while simultaneously minimizing tissue trauma? The
answer to this question, at the present time, may be fairly straight forward; the technique
with which SWL is applied can be critical to achieving optimal treatment outcomes.

A recent literature review and meta-analysis have reported that slowing the rate of SWL
delivery to 60 shockwaves per minute breaks stones more effectively than treatment at a rate
of 120 shockwaves per minute.12 The disadvantage of slowing the treatment rate is that
overall treatment time is increased. Although the reason why a slower treatment rate
increases stone fragmentation is not understood with certainty, hypotheses have been
suggested. Cavitation, the formation and subsequent dynamic behavior of bubbles, may be
induced by a lithotripter-generated pressure field. The bubbles that are initiated by 1
shockwave may persist long after the shockwave has passed and serve as nuclei, or
promoters, of cavitation. As subsequent shockwaves are delivered, the growth of additional
cavitation bubbles seeded by these nuclei may draw energy from the negative-pressure
phase of the shockwave. The ultimate effect of this energy sink may be reduced stone
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breakage. The process of cavitation and “bubble shielding” of a targeted stone has been
reported to be enhanced at fast shockwave rates.13

The process by which the patient is coupled to the lithotripter can also affect treatment out
come. The first-generation SWL devices were of a water bath design; patients were coupled
to the shockwave source by the water bath itself. However, most modern lithotripters use a
dry treatment head that is coupled to the patient with a medium of high-acoustic
transmission such as gel or oil. The great advantage of a dry treatment head when compared
with the water bath design of the Dornier HM3 is its transportable nature. Unfortunately, it
is difficult to achieve good coupling of the treatment head to the patient because typical
protocols often create air pockets at the coupling interface. Such defects can be a significant
barrier to shockwave transmission. In vitro studies have shown that coverage by air pockets
of just 2% of the coupling interface reduced stone breakage by 20% to 40%.14,15 When

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coupling is poor and energy transfer is attenuated, more shockwaves are therefore required
to fragment a stone, which may also have a traumatic effect on the kidney.
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The injury associated with SWL may be attenuated by a priming dose of low-amplitude
shockwaves; initiating treatment at a low power setting before shifting to a higher-power
setting has been reported to result in a significant reduction in lesion size.16 These findings
are clinically meaningful because they suggest a potential treatment strategy to reduce the
adverse effects of SWL. The physiologic mechanism responsible for this protective effect
has yet to be fully characterized, but assessment of renal hemo dynamics suggests that shock
waves induce transient vasoconstriction in the treated kidney.17,18 Increased vasculart one
may make the treated vessels less susceptible to cavitation or shear stress.

Conclusions
As surgical technology advances, the manner in which we treat patients suffering from stone
disease has become more efficient and less morbid. Intracorporeal lithotrites have the ability
to rapidly fragment and evacuate renal with flexible endoscopes in demanding applications,
such as access to the lower pole of the kidney for lithotripsy.

References
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15. Pishchalnikov YA, Neucks JS, VonDerHaar RJ, et al. Air pockets trapped during routine coupling
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16. Willis LR, Evan AP, Connors BA, et al. Prevention of lithotripsy-induced renal injury by
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Figure 1.
An in vitro testing apparatus for a “hands-free” testing approach to the evaluation of
intracorporeal lithotrites. Reprinted with permission from Kuo RL, Paterson RF, Siqueira
TM Jr, et al: In vitro assessment of ultrasonic lithotriptors. J Urol 170:1101–1104, 2003.
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Adv Chronic Kidney Dis. Author manuscript; available in PMC 2011 September 9.