High-energy shock waves for the treatment of nonunions: an experiment on dogs.

Several surgical as well as nonsurgical modes of treatment of nonunions have been advocated in the literature. In an effort to achieve bony union in a new noninvasive way, we experimentally investigated the treatment of nonunions with extracorporeally induced high-energy shock waves. With use of a modified canine nonunion model, two randomized groups of five dogs each were set up to obtain a treatment and a control group. Shock waves were applied with the Osteostar (Siemens A.G., Germany), a specially designed, experimental, transportable, high-energy shock wave apparatus. Each of the dogs in the treatment group received 4000 shock waves of 0.54 mJ/mm2 (14.5 kV), which were applied at four preselected sites, lying symmetrically on the dorsal and ventral sides of the nonunion. During the course of the experiments, the dogs were monitored radiographically. Immediately after the shock wave treatments no radiographic changes could be detected. All of the treatment group dogs reached radiographically observable bony union 12 weeks after the shock wave treatment. In the control group, four dogs had radiographically persistent nonunions at termination of the study. Statistical analysis with Fisher's exact test (two-sided; P < or = 0.05) demonstrated the significance in outcome between the two groups. We conclude that hypertrophic nonunions in dogs can be treated successfully with extracorporeally induced high-energy shock waves. The results of this study may justify the application of shock waves for the treatment of certain types of nonunions, provided a specially designed shock wave apparatus is used for this purpose. We think that it may become a reliable, nonsurgical, alternative for the treatment of certain types of nonunions.

Stone geometry and structure dependence on extracorporeal shock wave lithotripsy.

The in vitro fragmentation effects of electromagnetic-induced shock wave lithotripsy (Siemens Lithostar) were studied on parallel laminated schists in relation to the incoming shock wave energy and the incoming angle of the incident shock wave. Well above the threshold energy, the total amount of acoustic energy required for fragmentation remained unchanged regardless of the power setting of the high-tension supply. The amount of energy transmitted to the stone was limited by a total reflection angle, restricting the available transmission surface. These observations determine the effect of shock waves on calculi with an irregular shape such as staghorn stones. Lithotripsy-induced cavitation has been recognized, but no immediate influence on disintegration has become apparent until now.

Electromagnetic shock wave lithotripsy of gallbladder stones in vitro: the role of different stone characteristics and treatment variables.

From 40 sets of five human gallstones obtained at cholecystectomy, four stones were subjected to either 125/250 (maximum generator output) or 250/500 (half maximum generator output) electromagnetic shock waves (treatments I/II and III/IV, respectively); the fifth stone was used for computed tomography (CT) and chemical analysis. Overall, 130 (81%) of 160 stones fragmented, including 72 (45%) adequately (fragments less than or equal to 5 mm). For the treatments I, II, III, and IV the overall fragmentation rates were 80%, 95%, 70%, and 80%, respectively. The corresponding percentages of adequate fragmentation ( less than or equal to 5 mm) were 38%, 70%, 30%, and 42%, respectively. The best results were thus obtained after application of 250 shock waves (maximum generator output; treatment II). Pure cholesterol stones (p less than 0.01), stones with a mean CT density less than or equal to 110 HU (p less than 0.001), and stones with a calcified rim (p < 0.05) fragmented significantly better, but adequate fragmentation ( less than or equal to 5 mm) was significantly determined by stone weight and diameter (p less than 0.001), bilirubin content (p less than 0.02), and calcium content (p less than 0.05). A weight greater than 500 mg and a diameter > 10 mm could be defined as stone characteristics with significant negative predictors of adequate fragmentation. However, because the experimental conditions in this in vitro study did not completely simulate clinical settings for various reasons, these observations must be interpreted accordingly.(ABSTRACT TRUNCATED AT 250 WORDS)

Experiences with lithotripters: measurements of standardized fragmentation.

A comparison of lithotripters in terms of the fragmentation efficacy was established by using artificial stones. Two hundred pulses were applied to identical calcium sulphate cubes at varied energy levels of different lithotripters. In the cubics the shock waves formed regular craters, which could be analyzed with regard to depth, diameter, and volume. Dimensions of the craters increased with increasing energy. Each shock wave source designed a typical crater form. Different efficacies of fragmentation within different lithotripters could be recognized. High focal peak pressures did not guarantee better fragmentation effects. By using different acoustic lenses in the same electromagnetic lithotripter, the influence of different focus zones of the shock wave on the fragmentation could be investigated without any changes of the energy input. Results clearly emphasize the possibility of an increase of fragmentation efficacy by changing only the focal zones and the distribution of energy within the focal area.

Pressure distribution and energy flow in the focal region of two different electromagnetic shock wave sources.

In extracorporeal shock wave lithotripsy there is still a lack of knowledge about the basic physical terms that are essential for a scientific comparison of lithotripters with different technologies. The main goal of this article is to introduce the relation between pressure distribution, acoustic energy flow and intensity. The procedure of how these data can be achieved quantitatively is described. Technical data of two different commercially available electromagnetic shock wave sources are presented. The results show that acoustic energy flow and intensity depend on the variation of the shock wave parameters and the focal area.

Anesthetic requirements during electromagnetic extracorporeal shock wave lithotripsy.

An important aspect of modern extracorporeal shock wave lithotripsy is the ability to perform the procedure without anesthesia. Between June 1987 and April 1990, a total of 7,500 treatments were performed in our Lithotripsy Unit, using the Lithostar (Siemens AG, Erlangen, FRG): moreover 80% of the treatments were carried out as an anesthesia-free outpatient service. All treatments were reviewed for anesthetic requirements. Epidural anesthesia was performed in 74/7,500 (0.98%) treatments: during the initial period, the first 70 procedures were systematically performed under epidural anesthesia, and in 4 later cases of simultaneous endoscopic stone manipulation. Local skin infiltration was applied at the coupling site in 658/7,500 (8.7%) treatments. With increasing experience and technological improvement, 6,229/7,500 (83%) procedures were performed later on with only mild sedation: 1 mg of lorazepam orally 30 min before the treatment. Intravenous sedation was required in 510/7,500 (6.8%) cases because of painful local irritation, especially when treating calculi close to sites where shock waves can progress along the ribs. General anesthesia was required in all 28 children (0.4%).

The mechanisms of stone disintegration by shock waves.

Through interpretation of high-speed films at 10,000 frames per second of shock wave action on kidney stones and gallstones, the mechanism of stone destruction was analyzed in detail. This shows that the interaction of the shock wave with the targets firstly produces fissures in the stone material. Liquid then enters these small cracks. The actual disintegration is caused later by the enormous violence of imploding cavitation bubbles within these small split lines. That cavitation acts inside the stone and causes fragmentation even within the human gallbladder could furthermore be demonstrated by using scanning electron microscopy. These results should lead to a different process in gallstone lithotripsy leaving intervals between the shock wave treatments. This will allow the viscous bile fluids to occupy the fissures of the stones more completely and, therefore, should increase the cavitational activity on the subsequent treatment with shock pulses.

In vivo assessment of shock-wave pressures. Implication for biliary lithotripsy.

During extracorporeal shock-wave lithotripsy, the pressure profile, which is generated by the lithotriptor, determines the risk of tissue damage. In the present study, the pressure distribution of a lithotriptor (Lithostar; Siemens A.G., Erlangen, Federal Republic of Germany) was investigated in 10 pigs, five of which had gallstones surgically implanted into the gallbladder. The in vivo values were compared with in vitro data. Measurements were carried out along the shock-wave transmission path at the focus within the gallbladder, the adjacent liver, the diaphragmatic surface of the right lung, and the shock-wave exit site from the skin. Interposition of ribs did not cause a significant decrease in focal positive pressure. However, a gallstone positioned in the focus caused a 30%-65% reduction in pressure, recorded immediately behind the stone. Pressures obtained in vivo were always 15%-25% lower than those measured in vitro. The spatial distributions of the positive pressure in vivo and in vitro were almost identical. There was a high correlation between the pressures in vitro and in vivo (r = 0.88; P less than or equal to 0.01). This justifies assessment of shock-wave energies generated during biliary lithotripsy by extrapolation of in vitro data. It is concluded that it is possible to characterize different lithotriptors by in vitro pressure profile measurements.