Scientists recently confirmed that shock wave therapy has an analgesic (pain-killing) effect on horses that had been observed anecdotally, and they also found that the therapy does not have a harmful effect on bone. Scott McClure, DVM, PhD, Dipl. ACVS, assistant professor of surgery at Iowa State University, presented the results of these studies at the 2003 American Association of Equine Practitioners' convention. 

There's been a lot of speculation about the analgesic effects of extracorporeal shock wave therapy (ESWT) and radial shock wave therapy (RSWT)--no one has identified the duration or mechanism of analgesia. Some have thought that nerves and/or nerve receptors might be destroyed, but further study on the nerves of frogs (not horse feet) showed that nerves were not affected directly, but that small gas bubbles produced by the shock waves interacted with the nerves. Scientists weren't sure if this theory was applicable in live animals, particularly in the horse's distal limb.  

Early studies of ESWT in lab rodents showed microfracture of bones, but consequential studies in other species have not supported those findings. McClure his colleagues recognized that a change in elasticity or microstructure of equine bone, the bone might be weakened and more prone to catastrophic failure. 

The scientists showed that there is a potential risk associated with analgesia in the horse, which supports the post-treatment withdrawal periods enacted by racing jurisdictions and the Federation Equestre Internationale. "These data indicate that a horse should not be subjected to strenuous activities where local analgesia might pre-dispose the horse to injury for at least four days after ESWT or RSWT treatment," wrote the researchers in their summary paper. Exercise should be limited in animals under shock wave treatment to protect them from re-injury, and most horses under treatment require rest for the underlying problem anyway.

Nerve inflammation was determined to be a possible cause of analgesia after looking at the effect of shock waves on nerves and neurotransmitters in sheep. However, those results did not correlate with cutaneous (skin) sensation data collected in live horses. The researchers determined that further studies on the effect of shock waves on nerves in the horse are needed.

When the researchers looked at the effect of shock waves on the elasticity and microstructure of the bone in vitro (in the lab), they didn't find any effect on the mechanical properties of the bone, and no histological (tissue) changes that could be attributed to either ESWT or RSWT. In these studies, they used energy settings that were near the maximum that could be generated by the shock wave units, and treatment settings and duration were similar to what is used in the clinical setting. A previous study using even higher energy levels did not cause any fractures. "There was no physical effect on the equine cortical bone specimens, but further in vivo (in the living animal) evaluations would be indicated," McClure said. 

He noted that only one type of ESWT and one type of RSWT unit were used, and that energy levels and pulses vary between units. Using higher energy levels and an increased number of pulses could lead to a different outcome. "We need to use the equipment, but we need to use it wisely," he said.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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