Abstract
BackgroundRadial extracorporeal shock wave therapy (rESWT) is an attractive, non-invasive therapy option to manage fracture nonunions of superficial bones, with a reported success rate of approximately 75%. Using zebra mussels (Dreissena polymorpha), we recently demonstrated that induction of biomineralization after exposure to focused extracorporeal shock waves (fESWs) is not restricted to the region of direct energy transfer into calcified tissue. This study tested the hypothesis that radial extracorporeal shock waves (rESWs) also induce biomineralization in regions not directly exposed to the shock wave energy in zebra mussels.MethodsZebra mussels were exposed on the left valve to 1000 rESWs at different air pressure (between 0 and 4 bar), followed by incubation in calcein solution for 24 h. Biomineralization was evaluated by investigating the fluorescence signal intensity found on sections of the left and right valves prepared two weeks after exposure.ResultsGeneral linear model analysis demonstrated statistically significant (p < 0.05) effects of the applied shock wave energy as well as of the side (left/exposed vs. right/unexposed) and the investigated region of the valve (at the position of exposure vs. positions at a distance to the exposure) on the mean fluorescence signal intensity values, as well as statistically significant combined energy × region and energy × side × region effects. The highest mean fluorescence signal intensity value was found next to the umbo, i.e., not at the position of direct exposure to rESWs.ConclusionsAs in the application of fESWs, induction of biomineralization by exposure to rESWs may not be restricted to the region of direct energy transfer into calcified tissue. Furthermore, the results of this study may contribute to better understand why the application of higher energy flux densities beyond a certain threshold does not necessarily lead to higher success rates when treating fracture nonunions with extracorporeal shock wave therapy.
Highlights
Radial extracorporeal shock wave therapy is an attractive, non-invasive therapy option to manage fracture nonunions of superficial bones, with a reported success rate of approximately 75%
Using zebra mussels (Dreissena polymorpha) as a model for studying biomineralization [13], we recently demonstrated that induction of biomineralization after exposure to focused extracorporeal shock waves (fESWs) is not restricted to the region of direct energy transfer into calcified tissue [10]
Post hoc Bonferroni tests demonstrated statistically significant differences between the mean fluorescence signal intensity values obtained after exposure of mussels to radial extracorporeal shock waves (rESWs) produced at 4.0 bar and the mean fluorescence signal intensity values obtained after exposure to rESWs produced at, respectively, 0, 2.0, 2.5, 3.0 and 3.5 bar, but no statistically significant differences between mean fluorescence signal intensity values obtained after exposure to rESWs produced at respectively 0, 2.0, 2.5, 3.0 or 3.5 bar (Table 2)
Summary
Radial extracorporeal shock wave therapy (rESWT) is an attractive, non-invasive therapy option to manage fracture nonunions of superficial bones, with a reported success rate of approximately 75%. Wu et al Journal of Orthopaedic Surgery and Research (2021) 16:707 reports described successful treatment of fracture nonunions of superficial bones using radial ESWT (rESWT) [3, 6], in line with what was obtained in animal models [7, 8], with a reported success rate of approximately 75% [3, 6] Both fESWs and radial extracorporeal shock waves (rESWs) are single acoustic impulses which have an initial high positive peak pressure between 10 and more than 100 megapascals that is reached in less than one microsecond (μs) [9, 10]. FESWs differ from rESWs in terms of how the shock waves are produced, with regard to the penetration depth of the shock waves into tissue, and in terms of their physical characteristics [9, 11, 12]
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