To evaluate the clinical efficiency of a third generation electromagnetic shock wave lithotripter, the Lithoskop® (Siemens, Erlangen, Germany), regarding outcomes, stone disintegration, retreatment and complication rates.
To compare the results of the Lithoskop with other currently available systems and the reference standard lithotripter, the HM-3 (Dornier MedTech Europe GmbH, Wessling, Germany).
Patients and Methods
We analysed the data from 183 patients, including 13 children, undergoing extracorporeal shock wave lithotripsy (ESWL) for renal and ureteric calculi collected from a prospectively populated database.
Outcomes were assessed by plain abdominal film of kidney, ureter and bladder and renal ultrasonography for radiopaque and computerized tomography for radiolucent stones 1 day after treatment and after 3 months.
We analysed stone size and location before and after treatment, stone disintegration rate, retreatment rate, stone-free and residual fragment rates after 3 months, along with auxiliary procedures and complications.
The mean (range) patient age was 48.6 (1.3–81.4) years, including 13 children with a mean (range) age of 8.4 (1.3–16.7) years, and 77% of the patients were male.
In all, 46% of the calculi were localized in the kidney and 54% in the ureter. Renal stones were localized in the upper, middle and lower calyx and in the renal pelvis in 9, 29, 30 and 32% of patients, respectively. Ureteric stones were localized in the upper, mid- and distal ureter in 29, 19 and 52% of patients, respectively. The median (range) stone size before ESWL was 10 (4–25) mm in the kidney and 8 (4–28) mm in the ureteric calculi.
The overall stone-free rate after 3 months was 91% (88% for renal and 93% for ureteric calculi); the mean number of sessions to achieve these rates was 1.3.
Stone-free rates and the required number of sessions were determined only by stone size. In 7.1% of the patients (n = 13) post-interventional auxiliary procedures were necessary.
We observed one perirenal haematoma as a major complication (0.5%), but this did not require any further therapy.
Clinical stone-free rates with the Lithoskop are high and similar to those of other available systems, including the reference standard HM-3 lithotripter.
Retreatment and complication rates are low, supporting the use of ESWL as first-line therapy for urinary calculi <10 mm, independent of stone location.
In the 1980s ESWL was introduced to treat renal calculi. ESWL rapidly became the ‘gold standard’ treatment for nephrolithiasis [1-4]. High stone-free rates, as achieved with the first generation lithotripter, the HM-3 spark-gap device (Dornier MedTech Europe GmbH, Wessling, Germany), have never been achieved by any subsequent lithotripters. Many consider the HM3 to be the reference standard by which to judge every other recently developed lithotripter [5, 6]. Nevertheless, the original HM-3 has some drawbacks. It is a large immobile unit, with the patient treated in a water bath and an epidural or general anaesthesia is required owing to high pain levels. Consequently, new lithotripters with three underlying energy sources (electromagnetic, electrohydraulic/electroconductive and piezoelectric) have evolved. The aim of all new lithotripters was to increase the efficiency of stone fragmentation while minimizing tissue trauma and pain. The X-ray (fluoroscopy) quality was highly improved. Moreover the manufacturers improved the functionality and patient comfort by using coupling bellows; most current systems do not rely on water bath coupling [5-7].
In the current study, we evaluate efficacy and outcomes using a third generation electromagnetic lithotripter treating renal and ureteric calculi in a typical clinical setting. These third generation systems have improved technical refinements, such as a larger focus and deeper penetration. The treatment was performed according to the current European and American Guidelines . We believe that the present study population can be used to perform valid comparisons with other study populations, including those reported in early assessment of the HM-3 [4, 9-12]. To our knowledge, this is the second general evaluation of outcomes and efficacy of this lithotripter; however, four studies on this lithotripter are available in the literature [7, 12-14].
Patients and Methods
We evaluated outcome data from 183 patients consecutively treated using a third generation electromagnetic lithotripter (Lithoskop®, Siemens Medical Systems, Erlangen, Germany). All patients within a 10-month time period were included. Stone detection was performed with a dual ultrasound and fluoroscopic system. All patients underwent a complete follow-up, and the data were collected in a prospective database after obtaining the appropriate signed consent forms.
Patients were treated in the inpatient setting with at least one overnight stay owing to the German reimbursement system. The treatment was performed using the Lithoskop with an electromagnetic shock wave source (Pulso™). The stone detection system contains a dual device with an isocentric X-ray C-arm to perform ongoing fluoroscopy, if needed, and X-ray films and an inline ultrasound head, which can be inserted into the coupling bellow (Fig. 1) and rotated manually. The total focal length is 160 mm, focal width at -6dB is 8–12 mm (depending on energy settings) and is correlated with a peak pressure of 8–75 MPa. The large focus of this lithotripter permits administration of higher absolute energy doses at lower density, thus reducing side effects such as tissue injury. The technical specifications are shown in Table 1. To immobilize the patient and to reduce stone movement caused by respiratory motion we routinely used a compression belt, fixed over the abdomen of the patient.
Table 1. Technical specifications of the Lithoskop
The source of the generator is an electromagnetic spark with a water cushion coupling bellow. A spherical dish is used for focusing and an isocentric X-ray C-arm device is combined with an inline ultrasound head for imaging.
Focal width (−6 decibel)
Focal pressure (P+)
Adjustable in 38 steps (0.1–8.0)
Adjustable: 60/90/120 pulses per min
The shockwave intensity was gradually enhanced by steps of 300 per level from 0.1 up to 3.0, 3.5, 3.5 and 4.0 in the lower, middle and upper calyx and in the pelvis, respectively . Different maximum power settings were used as recommended by the manufacturer. The frequency used for kidney stones was 1.5 Hz; the total number of shocks was limited to 3500 impulses. Ureteric stones were treated with a 2-Hz frequency, and the intensity was enhanced to a maximum of 8.0 and 4500 impulses, depending on stone location owing to lower renal pole projection. In distal ureteric stones, which were treated in an overhead position, i.e. the shockwave source was coupled from above, the maximum energy level was limited to 5.0 to avoid any bowel lesions. Blood pressure was controlled intermittently every 3 min and a continued pulse oximetry was used for each treatment. Total energy, number of applied shockwaves, initial fragmentation rate, stone-free rates, residual fragment rates, analgesia requirements, number of sessions and any complications were assessed.
The therapy was performed according to the current European Association of Urology/AUA Guidelines, patients bearing renal stones with a diameter ≥20 mm (surface area ≥300 mm2) were offered a percutaneous nephrolithotomy (PNL) or received an internal ureteric JJ stent before therapy, if they opted for ESWL treatment. In patients with ureteric calculi with a diameter ≥10 mm, ureterorenoscopy (URS) was recommended as an option . If these patients chose ESWL, a stent was placed before treatment only in patients with therapy-resistant colic or elevated laboratory investigations, such as creatinine and/or inflammation markers. Exclusion criteria were bleeding disorders, anatomical malformations, PUJ obstruction, ureteric strictures, diverticular stones and any surgical intervention before ESWL. Furthermore, stents were placed in patients with obstructed and infected upper urinary tracts and/or for the prevention of renal function deterioration. In the absence of contraindications, all patients were offered ESWL as first-line therapy. Pre-interventional CT was only performed in a minority of patients. Hounsfield units were not taken into consideration to judge stone composition or to guide subsequent therapy. Children were always offered ESWL as first-line therapy if no obstruction or anatomical malformations were present. A maximum of three ESWL treatments and continued presence of residual fragments was considered as treatment failure and we moved on to endoscopic procedures such as PNL and URS, depending on stone location and size.
All patients were assessed by blood chemistry, urine analysis and renal function test before each treatment. A plain abdominal high definition X-ray film and ultrasonography were performed before each intervention to assess stone size and to exclude perirenal haematoma. In the absence of any contraindications an intravenous pyelogram (IVP) was obtained in every patient before the first therapy session. X-ray, ESWL and follow-up at 1 day and 3 months using plain X-ray films and ultrasonography, were performed by two experienced radiographers and urologists. Owing to the German reimbursement system and the higher costs related to CT, non-contrast CT was only performed in particular cases, where X-ray did not lead to a clear diagnosis or where contrast allergy was known to exist. ESWL treatment was considered as a failure if any residual fragments could be detected after 3 months. We determined the number of patients with residual fragments ≤4 mm (no further treatment required) and those that were stone-free, and calculated the stone-free rate. If there was any doubt about the presence or size of any residual stone fragments, the patient was automatically assigned to the residual fragment group, assuming this assignment would provide an underestimation of treatment success and stone-free rates. Auxiliary measures after treatment were assessed, in accordance with lithotripter terminology, as stated in the consensus document [17, 18]. Auxiliary procedures were defined as active stone removal by URS or PNL because of symptomatic residual fragments or any interventional therapy after ESWL. For the evaluation of outcomes we used an efficiency quotient (EQ) as defined by the formula: stone-free rate/(100% + re- treatment rate in percent + auxiliary measure rate in percent) .
Intravenous sedation-analgesia was continuously applied using remifentanil with an initial dose of 0.05 μg/kg/min by the treating urologist. The dose was adjusted depending on the reported pain level.
Continuous and categorical variables were compared between the groups using rank-sum and Fisher's exact tests, as appropriate. Data are reported as mean (sd) or median (interquartile range [IQR]) and number (percent) unless otherwise specified. Statistical analyses were performed using SPSS statistics version 19 (IBM Germany, Ehningen, Germany) and the R software version 2.11 (The R Foundation for Statistical Computing, Vienna, Austria). All tests were two-tailed. A P value <0.05 was considered to indicate statistical significance.
A total of 236 ESWL treatments were performed in 183 patients. The mean (range) patient age was 48.6 (1.3–81.4) years and the patients had a mean (range) BMI of 27.0 (16.7–51). The patients included 13 children with a mean (range) age of 8.4 (1.3–16.7) years. Overall, 140 (77%) patients were male and 43 (23%) were female. Among these, 84 patients (46%) had renal stones and 99 patients (54%) had ureteric stones. Stones were localized in 99 patients (54%) on the left side and in 84 patients (46%) on the right side. The stone distribution is shown in Tables 2 and 3.
Table 2. Renal and ureteric stone characteristics in children included in the study
*Residual fragments were ≤4 mm with no need for further treatment or auxiliary measures; in ureteric stones residual fragments were considered as treatment failure.
Of the 13 children, 10 had renal stones. The stones were located in the pelvis (n = 4), and in the middle (n = 3) and in the inferior (n = 3) calyx. Two children had distal ureteric calculi and one child had a mid-ureteric calculus. The median (range) stone size was 13.5 (6–20) mm, a second session was required in one child, twelve children needed only one session to achieve complete stone fragmentation (including two of the patients with residual fragments ≤4 mm). The median energy used was 35.5 J for renal stones and 42.5 J for ureteric stones. The mean (sd) number of sessions performed was 1.1 (0.3) and 1.0 (0.0) for renal and ureteric stones, respectively (Table 2). No complications occurred. Overall, a 77% stone-free rate was achieved. Auxiliary measures, such as PNL, after ESWL were needed in one child with a cystine stone. Three children received a ureteric stent before ESWL treatment because of unsustainable renal colic.
Overall, 84 patients with renal calculi underwent ESWL treatment; 32% (n = 27) of the stones were located in the renal pelvis, while 9% (n = 8), 29% (n = 24) and 30% (n = 25) were located in the upper, middle and lower calyx, respectively. The median (range) stone size in this group was 10 (4–25) mm and the median (IQR) energy used per session was 51 (42.2–58) J. No significant difference in levels of applied energy could be determined between locations. In all, 74% of patients required only one session, 22% required two and only 4% required a third session to achieve complete stone fragmentation (defined as stone-free + residual fragments ≤4 mm) with a stone-free rate of 88% after 3 months. The mean (sd) number of sessions to obtain stone clearance for calculi in the pelvis was 1.5 (0.6) compared with 1.1 (0.4), 1.2 (0.5) and 1.2 (0.4) for calculi in the upper-, middle and lower calyx, respectively (P = 0.17). The mean (sd) number of sessions for all renal calculi treated was 1.3 (0.5). In total, 94% of patients showed an initial fragmentation. The number of sessions required for complete disintegration correlated with the maximum stone diameter (P = 0.019). Stone size was significantly associated with stone-free rates (P = 0.036); the stone-free rate for calculi <10 mm (median [range] largest diameter: 8 [4–9] mm) was 92% (Table 3). By contrast, patients bearing calculi ≥10 mm ([range] largest diameter: 14 [10–25] mm) were stone-free in 85% of the cases. In all, 88% of patients (n = 74) were stone-free, and 7% (n = 6) had residual fragments ≤4 mm that could be detected 3 months after treatment. As a result, we would consider the overall treatment success rate to be 95% (n = 80).
Of the four patients for whom treatment was considered to have failed (residual fragments >4 mm), three harboured stones ≥10 mm. Auxiliary measures (2.4%) such as PNL (n = 1) and post-interventional JJ stent placement with a push back of fragments (n = 1) were successful. Seven percent of patients (n = 6) were treated with a JJ stent before scheduled ESWL treatment.
The EQ was 0.77, 0.84, 0.63 and 0.59 for upper, middle and lower caliceal and renal pelvis stones, respectively (Table 4 [5, 9, 10, 12]).
Table 4. Comparison of third generation electromagnetic lithotripters and the original HM-3 lithotripter for renal calculi
Overall, 99 patients with ureteric calculi underwent ESWL treatment. Of these, 29% (n = 29) were located in the proximal, 19% (n = 19) in the mid and 52% (n = 52) in the distal ureter. The median (range) stone size was 8 (4–28) mm and the median (IQR) energy used per session was 84 (57–113) J.
Seventy-nine percent of patients required one session, 14% required two sessions and only 7% of patients required three sessions to achieve complete stone fragmentation (defined as stone-free without any residual fragments) with a stone-free rate of 93% in total. The mean (sd) number of sessions for ureteric calculi overall was 1.3 (0.6). The mean (sd) number of sessions to obtain stone clearance for calculi in the proximal ureter was 1.4 (0.7) vs 1.3 (0.6) and 1.2 (0.5) in the mid- and distal ureter, respectively (P = 0.50). In all, 89% of patients showed initial fragmentation. The number of sessions required to attain stone-free status correlated with the maximum stone diameter (P = 0.001). Stone size was significantly associated with stone-free rates (P = 0.026) and the median (IQR) size in the stone-free group was 8 (5–10) mm compared with 10 (1–11.5) mm in the failure group.
Stone-free rates were 95% for calculi <10 mm (median [range] largest diameter: 6; [4-9]) dropping to 93% overall (median [range] largest diameter: 8 [4–28] mm). Stone-free rates for proximal, mid-, and distal ureter calculi were 93, 90 and 94%, respectively.
Of the seven patients in whom treatment was considered to have failed, four harboured stones ≥10 mm. 7% received a URS and 4% a post-interventional JJ stent. Twenty patients were treated with a JJ stent before ESWL treatment.
Taking all factors into consideration the EQs for proximal, mid- and distal ureter stones were 0.68, 0.68 and 0.73, respectively (Table 5 [9, 10, 12, 20-23]).
Table 5. Comparison of third generation electromagnetic lithotripters for ureteric calculi
Overall, 91% (n = 167) of the patients received remifentanil i.v. for analgesia and sedation, while 7% (n = 13) received general anaesthesia (all children), and 2% (n = 3) refused all pain medication. Remifentanil was given in a median dose of 7 mL/h (350 μg/h) with a sd of 2.66 mL/h (133 μg/h).
All interventions after ESWL treatment were counted as complications, including PNL (n = 1), URS (n = 7), and JJ placement (n = 1 for renal calculi and n = 4 for ureteric calculi, respectively) secondary to refractory colic or elevated creatinine levels. This represented a total of 7.1% (n = 13) of cases requiring auxiliary measures. One (0.5%) sub-capsular renal haematoma (major complication) was identified but did not require any intervention or blood transfusion.
Therapy discontinuation occurred in 4% of patients for hypertensive crisis (n = 2), pain (n = 1) and panic or non-compliance (n = 4). Overall, stone size correlated significantly with stone-free rates (Fig. 2). The median (IQR) stone sizes were 9 (6–12) mm in the stone-free group vs 10 (9–14) mm in the failure group (P = 0.036). Similarly, the required number of sessions correlated with stone size (P < 0.001). The median (IQR) stone size for patients requiring one session was 8 (6–11) mm compared with 10 (9–15) mm and 10 (9–14) mm for two or three sessions (P = 0.020). The stone-free rates in stented vs non-stented patients with renal and ureteric stones were 100 vs 87% and 95 vs 92%, respectively (both P = 1.0). Auxiliary measures were needed in 2.6 and 0% of the non-stented and stented patients with renal stones, respectively, and in 14 and 0% of the non-stented and stented patients with ureteric stones, respectively.
Patients with calculi <10 mm showed significantly better stone-free rates than those habouring calculi ≥10 mm (P = 0.019) as shown in Fig. 3. The mean (sd) number of sessions in these groups was 1.18 (0.48) vs 1.43 (0.63), respectively (P < 0.001).
The overall stone-free rate after 3 months was 90.7% (88% for renal and 93% for ureteric calculi).
As a result of significant improvements in shockwave technology and safety, ESWL can still be considered the first-line therapy for the treatment of most intra-renal stones and many ureteric stones. Some of these features include variable focal zones (size) and high disintegration power levels [23, 24]. Newer generations of lithotripters are facilitating outpatient-based treatments; lower analgesia requirements are needed and morbidity levels are low compared with those of the original HM-3 device. In terms of their stone fragmentation ability, however, the newer devices appear inferior to the original HM-3 device [8, 21, 25, 26]. Some recent clinical studies using the HM-3 have also shown higher stone-free rates, and lower rates of retreatment compared with newer-generation electromagnetic devices [5, 27].
In the present study we present the treatment outcomes using a third generation electromagnetic lithotripter, which is a stationary unit incorporating the Siemens Pulso concept with a long focal length of 160 mm and a broad beam width up to 12 mm. Using this wide focal size, the focal energy density could be lowered thus avoiding tissue injury. This also increases stone comminution owing to higher accumulated delivered energy when compared with lithotripters with a narrow focal width. Our initial detected fragmentation rate was 91% overall, 94% for patients harbouring renal calculi and 89% for ureteric calculi. Similar results have been reported by Bergsdorf et al.  with 94.7% (<5 mm) in 75 patients using the same shockwave delivery system, Pulso11®, which was implemented in a Siemens Lithostar Modularis platform in an experimental setup. Seitz et al.  reported an initial fragmentation rate of 95% in 218 patients using the Lithoskop.
In the present study we achieved overall stone-free rates of 88 and 93% for renal and ureteric stones, respectively (Table 3). Stone-free rates in children with renal and ureteric calculi were 70 and 100%, respectively. The mean (sd) number of treatments needed was 1.3 (0.5/0.6) for renal/ureteric calculi overall. Moreover, stone-free rates increased to 92 and 95% for renal and ureteric calculi <10 mm (Table 3). Our mean number of required treatments and the overall stone-free rates are similar, if not better, than most of the current lithotripters (Tables 4, 5 [9, 10, 12, 20-23]). The slightly higher re-treatment numbers, despite the excellent disintegration rates are probably attributable to the German reimbursement system, which requires the physician to keep the patients overnight in most parts of the country. If efficient fragmentation is not evident the day after treatment, another ESWL session is scheduled during the same hospital stay. This inevitably leads to overtreatment, as it is well known that stone fragmentation and passage are not necessarily achieved within the first 24 h of treatment. In fact some authors report a mean clearance time for ureteric stones after ESWL treatment of 4.6 days .
Stone-free status for renal stones of various locations (9, 29, 30 and 32% for upper, middle, lower calyx and renal pelvis) could be achieved in ≥80% with an EQ of 0.59–0.84. This is higher than the EQ reported by Danuser et al.  using the reference standard HM-3 in a recent study, and higher than the EQs from the Lithoskop study published by Seitz et al.  Additionally, our findings were similar to results using the HM-3 reported by Gerber et al. , defining stone-free rate as any fragments ≤2 mm (Fig. 4). Notably, when matching stone-free rates from a second study recently published by Seitz et al. , the current study showed a similar, or better, stone-free rate per group, although the total applied energy per stone was less than 50% of Seitz's in the current study. They applied a mean (SD) of 110 ± 83 vs 150 ± 89 J in non-stented vs stented renal stone cases to achieve a stone-free rate of 76.3 vs 77.3%, and 183 ± 131 vs 209 ± 125 J in ureteric stone cases to achieve a stone-free rate of 91.4 vs 93.5%, respectively. In the current study, the stone-free rate was 88% in renal and 93% in ureteric stone cases with a median (IQR) applied energy of 51 (42.3–58) J and 84 (57–113) J, respectively.
Resit-Goren et al.  postulated in a recently published study that it is safe and feasible to treat ureteric calculi ≤15 mm with ESWL as evidenced by their impressive results in treating 387 patients with ESWL. The mean (range) time to passage for patients with calculi 5–10 mm was 2.2 (1–3) days, for calculi 11–15 mm it was 7.7 (3–18) days and for calculi ≥16 mm it was 12.2 (11–37) days; however, in the present study the mean number of sessions for ureteric calculi was 1.3 compared with ∼1.69 in their study.
Badawy et al.  recently reported good results in 500 children aged between 9 months and 17 years with overall success rates (including residual fragments) of 83.4 and 58.46% for renal and ureteric calculi. They stated that children with a history of previous urological surgical procedures had lower success rates of stone clearance after ESWL. We showed success rates of 90 and 100% for renal and ureteric stones, respectively, but the number of children we treated with ESWL was small (n = 13) and all were naïve to surgical procedures.
Using currently available lithotripters, ESWL treatment can be performed with i.v. analgesia only. The medication we used is approved for in- or outpatient i.v. use under continuous monitoring. One of the limitations in comparing ESWL outcomes in published data is the lack of standardized treatment protocols and common imaging studies to report results. As mentioned above, we performed plain X-ray film and ultrasonography for each patient <24 h after treatment and after 3 months. Owing to the German reimbursement system, CT was only performed in a limited number of cases, such as those patients with radiolucent stones or no detectable fragments, in addition to ureteric dilatation. All images were verified and validated by the same two urologists (A.N. and J.W.). To reliably compare results between different studies CT imaging after 3 months would be desirable for all patients as the methods we used are likely to overestimate stone-free rates. It has been shown in a meta-analysis that low-dose CT has a pooled sensitivity of 96.6% (95% CI: 95.0–97.8) to detect calculi. When considering all calculi, an i.v. pyelogram has a detection rate of ∼70–90% and plain abdominal film of kidney, ureter and bladder has a detection rate of 50–70%. Regarding ureteric calculi only, ultrasonography has a detection rate of 50–60% .
Most of the referenced studies use the EQ to compare lithotripter-specific outcomes. This quotient takes stone-free rates into consideration, along with the need for repeat and adjunctive procedures, but the definition of residual fragments is not standardized. ESWL and any other more invasive kind of treatment do not take into account patient satisfaction or preference. Complication rates should also have some influence in efficiency-rates or quotients.
We predict that even better results could be achieved by treating renal stones with a shockwave frequency lowered from 1.5 Hz (used for this study accordingly to our current clinical practice) to 1 Hz, as we previously reported in a porcine model .
Our results are consistent with results reported from other recent studies using third generation lithotripters, achieving similar results to the reference standard HM-3 lithotripter [5, 7, 20, 22, 23, 27]. These findings encourage further research for improving treatment strategies and lithotripter design.
In conclusion, stone-free rates achieved using a third generation lithotripter (Lithoskop) were high with 88% for renal and 93% for ureteric calculi. These promising results support the use of ESWL as a first-line therapy for urinary calculi <10 mm, independent of stone location.
This work was supported in part by a Ferdinand Eisenberger grant from the Deutsche Gesellschaft für Urologie (German Society of Urology), ID NeA1/FE-11 (Andreas Neisius). Dr Matvey Tsivian provided a critical analysis of the statistics. Dr Nicholas J. Kuntz provided a critical reading of this manuscript.