POSSIBLE SIDE EFFECTS OF HIGH ENERGY EXTRACORPOREAL SHOCK WAVES ON INTACT BONE IN A RABBIT MODEL

Abstract

Shock wave treatment has been shown to induce new bone formation both under physiologic conditions and during fracture repair. Whereas various underlying molecular working mechanisms have been shown in recent studies, no study has assessed the influence of varying energy flux densities (EFD) on the amount of new bone formation in vivo. Therefore, the aim of this study was to investigate whether the effect of shock waves on bone is dependent on the applied EFD and if so, to identify the minimal dose necessary to induce new bone formation in vivo to avoid unwanted side effects of high-energy shock waves.

To this end, 30 New Zealand white rabbits were randomly divided in 5 groups and treated with extracorporeal shock waves at the distal femoral region (1,500 pulses at 1 Hz frequency each):

1. (a) control (sham treatment),

2. (b) EFD 0.35 mJ/mm2,

3. (c) EFD 0.5 mJ/mm2,

4. (d) EFD 0.9 mJ/mm2 and

5. (e) EFD 1.2 mJ/mm2.

To investigate new bone formation, animals were injected with oxytetracycline at the days 5 to 9 after shock wave application and sacrificed on day 10. Histological sections of treated and untreated femora of all animals were examined using broad-band epifluorescent illumination and contact microradiography. The amount of new periosteal and endosteal bone was measured and signs of periosteal detachment, cortical fractures, and fragmented trabecular bone with callus were recorded.

Application of shock waves showed new bone formation beginning with 0.5 mJ/mm2 EFD and increasing with 0.9 mJ/mm2 and 1.2 mJ/mm2. The latter EFD resulted in new bone formation also on the opposite cortical bone and cortical fractures and periosteal detachment occurred. EFD of 0.35 mJ/mm2 did not lead to any new bone formation. Here for the first time a threshold level is presented for new bone formation after applying shock waves to intact bone in vivo.

We conclude that the results presented here have significant impact on further clinical applications of shock waves on bone tissue. In the present study, it is clearly demonstrated that the amount of new bone formation is directly dependent on the applied EFD. If the applied EFD is to low, no significant new bone formation will occur. If it is too high, unwanted side effects, like the formation of bone spurs in the shoulder or nerve entrapment syndromes in the elbow or feet by bony overgrowth may result.