Original contributionElectrophysiological and Functional Effects of Shock Waves on the Sciatic Nerve of Rats
Introduction
Shockwaves are characterized by high positive pressures (∼100 MPa) and negative pressures (5 to 10 MPa), a rapid rise time (30 to 120 ns) and a short pulse duration (5 μs) (Sturtevant 1996). They were first used in lithotripsy to treat kidney stones (Chaussy et al. 1982) and subsequently to treat musculoskeletal disorders (Loew et al 1995, Rompe et al 1996a, Rompe et al 1996b).
The effects of extracorporeal shockwave therapy (ESWT) on bone, cartilage, connective tissue and vessels have been studied in human and rabbits, with the aim of understanding mechanisms that underlie treatments for musculoskeletal disorders (Durst et al 2002, Wang et al 2003). The effects of ESWT on peripheral nerves have also been reported recently. Applying ESWT to normal rat skin can induce degeneration of intracutaneous nerve fibers, with this effect reversing within two weeks (Ohtori et al 2001, Takahashi et al 2006). It was postulated that this effect is responsible for the immediate pain relief after ESWT. However, the myelin sheath can be damaged histologically by ESWT in horses and dogs (Bolt et al 2004, Wang et al 2002), and further functional damage induced by such histologic changes would challenge the safety of ESWT. The range of clinical indications has widened, with ESWT being applied to different body regions. However, the possibility of damage to the nerve remains unknown because the nerves cannot be seen from the body surface. If damage to peripheral nerves does occur, it is not known whether these changes are long lasting, cause functional damage or relate to the intensity of ESWT.
The purpose of this study was to evaluate the short-term effects of shockwaves on the electrophysiological, histologic and functional properties of mixed peripheral nerves. We hypothesized that shockwaves could induce reversible segmental demyelination of peripheral nerves, with this effect being correlated with the shockwave intensity.
Section snippets
Experimental animals
All procedures were approved by the Laboratory Animal Center of National Taiwan University College of Medicine. All the animals had free access to food and water during the study. Eighty-four adult male Wistar rats weighing 359 ± 62g (mean ± SE) were used in this study. Sixty-six animals were randomized into three different-intensity treatment groups. Seven rats in each group were evaluated with motor nerve conduction velocity (MNCV) before and immediately after (day 0) and at 1, 4, 7 and 14 d
Shockwave treatment
The perineurium of the treated nerve segment exhibited swelling and discoloration but no bleeding immediately after treatment in all animals in the high-intensity group (Fig. 2) and in one third of the animals in the moderate-intensity group. The swelling and discoloration disappeared within 4 d, and no visual change was evident in adjacent tissues. No rat died or demonstrated self-injuring behaviors during the study period.
Motor nerve conduction studies
A moderate decrease in the MNCV was evident in all treatment groups
Discussion and Conclusion
Our evaluations of the effects of shockwaves on peripheral nerves showed that shockwave treatment induced temporary decreases in MNCV. This effect lasted for 4–7 d. Light microscopy and TEM revealed demyelination of large-diameter myelinated fibers, which recovered within 14 d. The demyelination could be the reason for conduction slowing in our study, which is similar to the results of an investigation of digital nerves treated with nonfocused ESWT in horses (Bolt et al. 2004). In the present
Acknowledgements
This research could not have been finished without the help from the National Science Council (grant No. 94-2314-B-002-087).
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