CT attenuation value and shockwave fragmentation

PURPOSE: To evaluate whether, in principle, the mean CT attenuation values of kidney stones could predict fragmentation by shockwaves. MATERIALS AND METHODS: Four types of artificial kidney stones having different CT attenuation values were tested. Artificial stones were weighed and exposed to 700 shockwaves at 21 kV at the focus of an electrohydraulic lithotripter. Fragments were strained through meshes with 2x2-mm and 3.1x3.1-mm openings. The material left on the meshes after shockwave exposure was dried and weighed on a precision scale. Half of all artificial stones were saturated by immersing them in water several days before fragmentation. Fragmentation coefficients (i.e., percent weight loss) were associated with CT attenuation values using a statistical model. RESULTS: Higher CT numbers resulted in lower fragmentation coefficients. Artificial stone weight was inversely proportional to the percent weight loss. Larger fragments were obtained at lower fragmentation coefficients. Statistical analysis revealed that fragmentation can be predicted knowing the weight and the CT number of a stone before shockwave application. CONCLUSION: Prediction of the number of shockwaves necessary for successful SWL could be possible. Our statistical model proved to fit in vitro fragmentation of artificial stones; however, clinical application requires further research.     

In-Vivo relation between CT attenuation value and shockwave fragmentation

PURPOSE: To use CT attenuation numbers as a means of determining the susceptibility of an artificial stone to in-vivo fragmentation with extracorporeal shockwave lithotripsy (SWL). MATERIALS AND METHODS: Four types of artificial kidney stones having different CT attenuation values were used. One randomly selected stone was implanted in the renal pelvis of a kidney of 12 young pigs and exposed in vivo to 2500 shockwaves (21 kV) using an electrohydraulic lithotripter. Bilateral nephrectomy was performed after SWL. Fragments were strained through a mesh with a 3.1-mm grid, and the debris left on the mesh was dried and weighed. Fragmentation coefficients (FCs) were associated with CT attenuation values using a statistical model. RESULTS: The relation between FC and CT number was significant, indicating that as CT attenuation increases, FC is reduced. Larger stone fragments were obtained from stones with higher CT numbers. Initial stone weight was not a significant explanation for variations in FC. CONCLUSION: The CT values could be helpful in selecting patients for SWL in the future. However, other parameters such as stone porosity, shape, and roughness also will have to be considered.     

Small-bowel perforation after shockwave lithotripsy

A 51-year-old woman with a history of stone disease sustained two 3 x 2-mm ileal perforations during SWL (6000 shockwaves; 0.33-0.42 mJ/mm2) for a 14 x 8-mm left-sided midureteral stone. Low energy levels should be applied when ureteral stones are treated by SWL with the patient prone.     

Synchronous twin-pulse technique to improve efficacy of SWL: preliminary results of an experimental study.

BACKGROUND AND PURPOSE: Extracorporeal shockwave lithotripsy (SWL) is the treatment of choice for the majority of renal and ureteral stones. The Dornier HM3 lithotripter has good results but with some limitations and complications. A number of second- and third-generation machines have been developed employing different energy sources, focusing devices, and coupling media. These devices overcome some of the limitations and lessen the complications but at the expense of the success rate. Use of the consecutive double-pulse technique (as in the MFL 5000) and of combined under-table and over-table modules consecutively (as in the Siemens Lithostar Plus) improves the efficacy of fragmentation. The aim of this study was to study the effects of the use of synchronous twin pulses generated by under-table and over-table identical shockwave reflectors for stone fragmentation. MATERIALS AND METHODS: We designed a lithotripter with two identical shockwave generators and identical reflectors (twin heads). One reflector was under the table and fixed, while the second reflector was over the table and hangs on a C-arm so that the angle between the axes of the two reflectors could be changed. The second focal points (F2) of the two reflectors lay in the same position. A lucent lightweight acrylic water tank with one side sealed by a silicon rubber membrane was fixed to the SWL table so that the membrane coupled with the water cushions of both reflectors. The tank was filled with degassed water and the targeted material was fixed on a holder and immersed in the water so as to be at F2. Comparison of the use of one shockwave source and two shockwave sources simultaneously was done relative to: (1) cavitation effect on aluminum foil; (2) quality of disintegration, shape of the focal zone, and ideal position of F2 using ceramic blocks; and (3) disintegrative efficacy using dental bone cement. RESULTS: The cavitation effect became more localized with the use of two reflectors. Also, the volume and rate of stone disintegration increased with the use of the two reflectors, with production of fine (<2-mm) fragments. The focal zone became smaller and conical with no propagation of shockwaves beyond F2. These results were more evident if the angle between the axes of the reflectors was 90 degrees. CONCLUSION: This new technique of SWL may improve the efficacy of treatment of urinary tract stones. It also may be less harmful to the renal tissues, but animal experiments must be carried out to prove this.     

Does failure to visualize the ureter distal to an impacted calculus constitute an impediment to successful lithotripsy?

BACKGROUND: A severe degree of ureteral obstruction is viewed as a predictor of poor outcome in shockwave lithotripsy (SWL). Impacted stones are often considered a contraindication to in-situ SWL. PATIENTS AND METHODS: Impaction in our study was defined as failure to visualize the ureter distal to the calculus with proximal hold-up of contrast for as long as 3 hours on an intravenous urogram (IVU). We evaluated 30 patients with impacted ureteral calculi, who were compared with a second unimpacted group matched for stone size and stone location. The calculi were reorganized into < or =10-mm and >10-mm groups. The results were compared in terms of clearance rates, number of shockwaves, number of sessions, and number of days between the start of SWL and clearance. RESULTS: Between January 1998 and December 2001, 30 impacted stones were treated with lithotripsy. Complete clearance rates in the impacted as well as the non-impacted group were 76.7%. There was no statistical difference in the number of shockwaves, sessions, or time to clearance. The results were poorer in lower-ureteral than upper-ureteral calculi, but this difference did not reach statistical significance. However, the differences between the < or =10-mm and >10-mm stones were statistically significant. CONCLUSION: Impaction on an IVU does not affect the results of lithotripsy.     

Effect of urine specific gravity on effectiveness of shockwave lithotripsy

PURPOSE: To determine the effect of urine specific gravity (SG) and radiographic contrast medium on the efficiency of extracorporeal shockwave lithotripsy (SWL) fragmentation using a previously published in vitro model. MATERIALS AND METHODS: Artificial kidney stones (BegoStone [BEGO USA, Smithfield, RI]) of a standard size (10 x 10 mm) and weight (mean 1.90 g; range 1.89-1.91 g) were randomly allotted to one of four test media with differing SG: group 1: synthetic urine, SG 1.003; group 2: synthetic urine, SG 1.040; group 3: 50% radiographic contrast (Cysto-Conray II, Mallinckrodt Inc., Hazelwood, MO), 50% synthetic urine, SG 1.069; and group 4: 100% contrast, SG 1.121. The stones were placed in cups made of 2.2-mm screen mesh and exposed to 500 shockwaves at 20 KV from a spark-gap lithotripter (Econolith 2000; Medispec, Germantown, MD). The stone fragmentation rate (i.e., percent fragmentation) was determined by dividing the dry residual stone weight by the prelithotripsy dry weight (X 100). RESULTS: The mean fragmentation rate for the four groups was 31.7%, 37.6%, 31.8%, and 27.2%, respectively. Statistical significance was not achieved (P = 0.1). CONCLUSION: Stone breakage tends to be more effective when urine SG is about 1.040 than at higher or lower values. Hence, the recommendation for an overnight fast prior to SWL is well founded. Introduction of contrast medium may inhibit stone breakage because it increases the specific gravity.     

Bifocal reflector for electrohydraulic lithotripters

OBJECTIVE: To describe the design and construction of a bifocal reflector that could be used in electrohydraulic extracorporeal shockwave lithotripters in order to increase their efficiency. METHODS: The new reflector is obtained by joining two sectors of two rotationally symmetric ellipsoidal reflectors having different distances between their foci, which results in a bifocal composite reflector with the F1 foci in coincidence and the two F2 foci separated by a certain distance. As in conventional reflectors, shockwaves are generated by the electrical breakdown of water between two electrodes, located at the focus (F1) closest to the reflector. A prototype was constructed and tested in an experimental shockwave generator of our own make, using two different types of kidney-stone models, one to test the stone fragmentation abilities, and the other to test the stone pitting abilities. Fragmentation data for the new reflector were compared with those of a conventional ellipsoidal reflector tested on the same device. RESULTS: The new design appeared to be more efficient in breaking up both types of kidney-stone models than the conventional reflector. Pressure measurements were obtained with both reflectors using needle hydrophones. The physical background of shockwave reflection on both reflectors is also explained. CONCLUSION: With this new reflector, it could be possible, in principle, to reduce the treatment time of extracorporeal shockwave lithotripsy.     

Vertebral fracture associated with shockwave lithotripsy in a patient with granulomatous spondylitis.

Extracorporeal shockwave lithotripsy (SWL) is an accepted treatment modality in the treatment of urinary stone disease. Many complications have been reported secondary to high-energy shockwaves, but the effects of SWL on the skeletal system have rarely been investigated. We represent the first case of a burst-type vertebral fracture after SWL in an elderly osteoporotic patient with granulomatous spondylitis.     

Is measurement of stone surface area necessary for SWL treatment of nonstaghorn calculi?

BACKGROUND AND PURPOSE: The size of urinary tract stones is usually assessed by the longest diameter (LD) alone. Logically, however, two-dimensional measurement of the stone surface area (SSA) susceptible to shockwaves would give more useful information for the planning of treatment by extracorporeal shockwave lithotripsy (SWL). This has been shown for staghorn calculi. The aim of this study was to determine for nonstaghorn kidney and ureter stones whether the LD alone identifies as reliably a subgroup of patients with a stone of a certain size as does the SSA. Furthermore, we sought to determine whether the LD alone indicates as reliably the number of patients who would be rendered stone free after one SWL session within a certain subgroup as would the SSA. PATIENTS AND METHODS: Retrospectively, SWL treatment and radiographic data of 330 patients who had undergone SWL for a single stone were analyzed. RESULTS: Ureteral stones were significantly smaller on average, and ureteral stone patients needed fewer SWL treatment sessions and fewer shockwaves to become stone free. Stratification of both kidney and ureteral stones by either LD or SSA resulted in comparable groups of patients. There were no significant differences in patient, stone, or treatment data. More importantly, the stone-free rates after one treatment did not differ significantly. CONCLUSION: The LD does accurately reflect the size of a nonstaghorn kidney or ureteral stones. Therefore, the measurement of LD, as generally practiced, appears clinically sufficient and appropriate for the assessment of stone size prior to SWL in both kidney and ureteral stones.     

Salvage extracorporeal shockwave lithotripsy after failed distal ureteroscopy

BACKGROUND AND PURPOSE: When intervention is necessary, controversy remains as to the best treatment modality for stones of the distal ureter. In general, ureteroscopy is favored over extracorporeal shockwave lithotripsy (SWL) as the treatment of choice for distal ureteral stones. Although uncommon, ureteroscopy failures have traditionally necessitated repeat ureteroscopy to retrieve retained stone fragments. We evaluated the efficacy of salvage SWL for failed primary distal ureteroscopy in the community setting. PATIENTS AND METHODS: From December 1989 to December 2000, 6099 patients underwent SWL with the Dornier HM4 lithotripter at our institution. We retrospectively identified 31 patients who had undergone the SWL after a failed distal ureteroscopy. RESULTS: The average stone size in these patients was 9.4 mm, the average time interval from ureteroscopy to SWL was 17.2 days, and the average number of shockwaves delivered was 2386. All patients had had stents placed after ureteroscopy. Twenty-seven patients (87%) had resolution of their stone burden after one SWL session. The remaining four patients underwent additional procedures. CONCLUSIONS: Ureteroscopy is an effective modality for the treatment of distal ureteral stones. However, when unsuccessful, a salvage procedure may be necessary. Extracorporeal lithotripsy is a less invasive procedure with comparable success rates in the distal ureter. This report suggests that salvage SWL is an appropriate option for patients in whom distal ureteroscopic stone extraction fails.     

Effect of vibration massage therapy after extracorporeal shockwave lithotripsy in patients with lower caliceal stones

PURPOSE: To determine whether vibration massage influences the results of extracorporeal shockwave lithotripsy (SWL) in patients with lower caliceal stones. PATIENTS AND METHODS: One hundred three patients with lower caliceal stones were entered in the study. Patients were divided into two groups that received either SWL alone (Group A, N = 52) or with vibration massage (Group B, N = 51). There was no statistically significant difference between the two groups in stone size, duration of follow-up, or patient age. The complication, stone-free, and stone recurrence rates of the groups were compared. RESULTS: There was no statistically significant difference between the groups in the number of shockwaves, number of SWL sessions, or shockwave energy. The renal colic rate was higher in Group B than in Group A (P = 0.03). The stone-free rates in Group A and Group B were 60% and 80%, respectively (P = 0.003). The stone recurrence rate was higher in Group A than in Group B (P = 0.0006). CONCLUSIONS: This retrospective study demonstrates that SWL with vibration massage appears to have a beneficial effect on the passage of fragments in patients with lower caliceal stones.     

Therapeutic efficacy of Dornier MPL 9000 for prevesical calculi as judged by efficiency quotient

PURPOSE: To study the efficacy and safety of the Dornier MPL 9000 lithotripter in the treatment of prevesical calculi using real-time ultrasound monitoring and to see if efficacy is adequately judged by the efficiency quotient (EQ). PATIENTS AND METHODS: Seventy-six patients underwent ultrasound-guided extracorporeal shockwave lithotripsy (SWL) for prevesical calculi over a period of 43 months. Their age ranged from 8 to 68 (mean 37.6) years, and the male:female ratio was 2.6:1. The size of the stones, measured in two dimensions, ranged from 4 to 25 mm (mean 9.3 mm) and 2 to 15 mm (mean 6.0 mm). No general or regional anesthesia or ureteral stents were used, and all patients were treated in the prone position. The EQ was calculated using the formula: Stone free (%) x 100/(100 + retreatment rate (%) + auxiliary procedures (%). RESULTS: Seventy patients were stone free in a mean time of 15 +/- 14.11 days. The average number of shockwaves used was 2,831 +/- 1,612, and the average number of sessions per patient was 1.7. About 92% of the patients were rendered stone free using in situ SWL alone. No major complication was encountered, and none of the patients required an inpatient stay after SWL. The EQ was 65. Five patients with failed SWL subsequently were rendered stone free, four with salvage ureteroscopy and pneumatic lithotripsy and one with cystolitholapaxy for a symptomatic fragment in the bladder. One patient was lost to follow-up. CONCLUSION: In situ SWL is a safe and effective treatment for prevesical calculi. It should be used as a first-line treatment for most such stones. Efficiency can be assessed objectively by the EQ.     

Pediatric shockwave lithotripsy: size matters!

BACKGROUND AND PURPOSE: Shockwave lithotripsy (SWL) is a safe and efficacious modality for pediatric urolithiasis. Recent reports claim good results even with larger stone burdens, irrespective of stone location. We reviewed the outcomes of SWL in the pediatric population at our center to assess the impact of stone burden and location and the age of the child on the stone-free rate. PATIENTS AND METHODS: Records of 106 patients 相似文献   

Effect of stone motion on in vitro comminution efficiency of Storz Modulith SLX

BACKGROUND AND PURPOSE: During SWL, stone motion secondary to ventilatory motion can be as much as 50 mm. This is much larger than the 4- to 15-mm diameter of the focal regions on most clinical machines. The goal of this study was to determine the effect of stone motion on the fragmentation efficiency of a clinical lithotripter with a small (4-mm) focal spot. MATERIALS AND METHODS: A model stone (6.5 x 7.5 mm) made of gypsum cement was used as an in vitro target for a Storz Modulith SLX lithotripter with a custom-designed waterbath. A motorized positioner was used to translate the stone in order to simulate ventilatory motion. The excursion was variable up to 48 mm (+/- 24 mm about the focus). After treatment by 400 shockwaves, the remnants (> 2 mm) were dried and weighed. RESULTS: Fragmentation efficiency was reduced (P < 0.05) for motion of > or = 10 mm. Similar results were found with different energy levels and firing rates. The reduction in fragmentation efficiency was consistent with calculations of the time the stone was outside the focal region. CONCLUSIONS: Clinically relevant stone motion has a dramatic effect on in vitro comminution. Motion of 10 mm led to a significant reduction in comminution, and for motion > 20 mm, it appeared that three-quarters of the shockwaves missed the stone. These data imply that ventilatory gating or stone tracking may result in fewer shockwaves being required for successful treatment with this lithotripter.     

Combined ureterorenoscopy and shockwave lithotripsy for large renal stone burden: an alternative to percutaneous nephrolithotomy?

PURPOSE: To investigate the feasibility and initial outcomes of a combination of ureterorenoscopy (URS) using holmium laser lithotripsy and extracorporeal shockwave lithotripsy (SWL) in a single outpatient session for the treatment of large renal stone burdens in patients refusing or unsuitable for percutaneous nephrolithotomy (PCNL). PATIENTS AND METHODS: Fourteen patients with a mean age of 52.7 years (range 34-81 years) having a mean stone burden of 847 mm2 (range 58 mm2-1850 mm2) were treated with combined URS laser lithotripsy and SWL as an alternative to PCNL. The SWL (mean 2800 shockwaves) was performed using the Storz Modulith SL-X, and flexible URS with holmium laser lithotripsy was performed either during or following SWL. RESULTS: Ninety-three percent of the patients (13/14) were treated successfully on an outpatient basis. Two patients were rendered stone free after the initial procedure alone (14%). Overall, including secondary outpatient treatment with a second session of URS alone (N = 7) URS and SWL (N = 1), SWL (N = 1), or oral alkalinization therapy (N = 1), the stone-free rate was 76.9% (10/13). One patient was excluded secondary to death from unrelated causes after the initial procedure, and the success rate (residual fragments <4 mm) was 84.6% (11/13). The two treatment failures included one patient who required a third URS procedure and one patient who developed urosepsis necessitating nephrostomy-tube placement who underwent subsequent PCNL. CONCLUSIONS: In comparison with traditional approaches using PCNL and second-look nephroscopy, single-session combined URS and SWL with a second outpatient procedure may offer equivalent results with decreased morbidity in carefully selected patients.     

Prefocal alignment improves stone comminution in shockwave lithotripsy

BACKGROUND: The Dornier HM-3 machine continues to be one of the most effective lithotripters in use. However, tissue damage occurs in most, if not all, shockwave lithotripsy (SWL) treatments. Cavitation appears to contribute to desired stone comminution as well as to undesired tissue damage. Studies of cavitation in electrohydraulic shockwave lithotripters indicate that the greatest cavitation activity occurs, not at the geometric focus, F2, but at a site proximal to F2 by 1 to 3 cm. In clinical practice, however, stones are aligned with F2. MATERIALS AND METHODS: In vitro stone comminution, hemolysis, and free-radical production were assessed along the focal axis, and pig kidneys treated with SWL in vivo were sectioned to determine the extent of hemorrhagic injury along the focal axis. Model gypsum stones received 200 shockwaves in vitro at 18 kV. RESULTS: At F2, the average number of fragments >1.5 mm was 1.3 +/- 0.5, and the weight loss was 11.3 +/- 1.1%. At 2 cm from F2 (F2-2 cm), these values increased to 4 +/- 2.8 and 16.1 +/- 4.2%, respectively. Samples of 10% hematocrit blood were similarly exposed. Hemolysis was equivalent at F2-2 cm (14.7 +/- 2.3%) and F2 (15.2 +/- 3%) but decreased significantly at all other positions. Samples of iodine solution received 1500 shockwaves at 20 kV. Hydroxyl radical production was greatest at F2-2 cm (0.384 +/- 0.035 microM) and decreased significantly distal to this position. The volume of tissue injury in pig kidneys was greatest with prefocal shockwave exposure. CONCLUSION: Stone comminution may be achieved more rapidly without greater tissue damage by a simple shift in stone alignment to F2-2 cm.     

Extracorporeal shockwave lithotripsy for solitary distal ureteral stones: does the degree of urinary obstruction affect success?

BACKGROUND AND PURPOSE: Extracorporeal shockwave lithotripsy (SWL) is a safe and effective way to treat stones in the distal ureter, but the impact of urinary obstruction on outcome is not clear. We investigated the relation between the degree of stone-induced urinary obstruction and the outcome of SWL treatment in patients with solitary distal ureteral stones. PATIENTS AND METHODS: A series of 165 consecutive patients with solitary distal ureteral stones underwent SWL (Multimed 9200 Lithotriptor, Elmed Medical Systems, Turkey) between October 2002 and September 2003 at two separate centers. Distal ureteral stones were defined as those located below the lower border of the sacroiliac joint. Patients were divided into four groups according to the degree of stone-induced urinary obstruction: group I (N = 62) had no urinary system dilation; group II (N = 40) had mild dilation, group III (N = 35) moderate dilation, and group IV (N = 28) severe dilation. In addition to degree of obstruction, stone size, average fluoroscopy time, total number of shockwaves applied, number of sessions required to achieve stone-free status, and stone clearance time were recorded. Treatment failure was defined as persistence of fragments after three SWL sessions. RESULTS: Overall, 152 (92.1%) of the patients became stone free after SWL. There were no statistically significant differences among the groups with respect to any of the factors studied. CONCLUSION: In cases where there is a solitary calculus in the distal ureter, the degree of urinary obstruction caused by the stone does not affect the success of stone clearance with SWL.     

Extracorporeal shockwave lithotripsy in pediatrics

Since its introduction in 1980, extracorporeal shockwave lithotripsy (SWL) has become the first therapeutic option in most cases of upper-tract urolithiasis, and the technique has been used for pediatric renal stones since the first report of success in 1986. Lithotripter effectiveness depends on the power expressed at the focal point. Closely correlated with the power is the pain produced by the shockwaves. By reducing the dimensions of the focus, it becomes possible to treat the patient without anesthesia or analgesia but at the cost of a higher re-treatment rate. Older children often tolerate SWL under intravenous sedation, and minimal anesthesia is applicable for most patients treated with second- and third-generation lithotripters. Ureteral stenting before SWL has been controversial. Current data suggest that preoperative stent placement should be reserved for a few specific cases. Stone-free rates in pediatric SWL exceed 70% at 3 months, with the rate reaching 100% in many series. Even the low-birth-weight infant can be treated with a stone-free as high as 100%. How can one explain the good results? Possible explanations include the lesser length of the child's ureter, which partially compensates for the narrower lumen. Moreover, the pediatric ureter is more elastic and distensible, which facilitates passage of stone fragments and prevents impaction. Another factor is shockwave reproduction in the body: there is a 10% to 20% damping of shockwave energy as it travels through 6 cm of body tissue, so the small body volume of the child allows the shockwaves to be transmitted with little loss of energy. There are several concerns regarding the possible detrimental effect of shockwaves on growing kidneys. Various renal injures have been documented with all type of lithotripters. On the other hand, several studies have not shown adverse effects. In general, SWL is considered to be the method of choice for managing the majority of urinary stones in children of all ages. Re-treatments improve the stone-free rate, often raising it to 100%. Among the predictors of success, stone size seems to be the most important. In the absence of guidelines, selecting the appropriate treatment modality for each child requires planning and depends on instrument availability and local expertise.     

Percutaneous stone implantation in the pig kidney: a new animal model for lithotripsy research

PURPOSE: This report describes a new animal model for research on the parameters of shockwave delivery and the mechanisms of shockwave action in SWL. MATERIALS AND METHODS: Female pigs (approximately 45 kg) were anesthetized for creation of an upper pole peripheral caliceal access. The tract was dilated with a 30F Nephromax balloon and Amplatz sheath, and a 24F rigid nephroscope was used to guide a gypsum artificial stone into a lower pole calix. An internal ureteral stent was then placed. After a 2-hour recovery period, lithotripsy was performed using an unmodified Dornier HM3 lithotripter. Following SWL, en bloc excision of the urinary tract was performed, and the stone fragments were collected. RESULTS: As observed by nephroscopy, most stones were surrounded by urine that was free of clot or debris. Urine output was >1 mL/kg per minute by the time the animal was positioned for SWL after a 2-hour observation period. When the conditions of shockwave (SW) exposure were 400 SWs, 20 kV, and 120 SW/min, the efficiency of stone fragment recovery was 85% +/- 2% (N = 6 stones). CONCLUSIONS: This procedure provides a minimally invasive method for placement of model stones of clinically relevant size within the pig kidney. Stone implantation is efficient and permits experiments to be conducted in 1 day. Stone fragmentation can be quantitated, and the animal can serve as its own control. Long-term experiments are also feasible. Overall, this new animal model is appropriate for experimentation on the parameters of SW delivery in SWL.     

Shockwave lithotripsy: anecdotes and insights

Shockwave lithotripters have evolved considerably since the introduction of the Dornier HM3 machine 20 years ago. Although shockwave lithotripsy (SWL) remains the preferred treatment for the majority of symptomatic upper urinary-tract calculi, newer lithotripters are not as effective and may have a higher risk of side effects. Lack of progress in lithotripter evolution is attributable to inadequate understanding of how and why shockwaves produce effects on stone and tissue. Current knowledge suggests that stones fragment by the mechanisms of compression fracture, spallation, squeezing, and acoustic cavitation, while tissue damage from shockwaves is secondary to cavitation and non-cavitational forces such as sheer stress. It appears likely that most tissue damage from shockwaves is caused by cavitation. As the understanding of SWL matures, new lithotripter designs may emerge that truly represent an improvement on the original Dornier HM3 machine.