Shockwave Therapy: New Research Suggests Possible Link to Catastrophic Injury

In California, a proposed new rule would, if passed, prohibit horses at California Horse Racing Board (CHRB)-regulated facilities from racing or working within 30 days of being treated with extracorporeal shockwave therapy. At the moment in California, horses are unable to race or work for 10 days after a shockwave therapy. Should the rule go into effect, it would be by far the toughest of its kind throughout the country.

At the same time, the proposed rule change reignites the debate on one of the more controversial veterinary technologies in modern veterinary medicine, raising hard questions about the suitability of such machines on U.S. racetracks and training centers at a time of laser-focused scrutiny on animal welfare.

On the one hand are those who see therapeutic value to shockwave therapy as long it's used with an appropriate diagnosis and treatment plan. On the flip side are those who see the machine's analgesic effects as reason enough to fundamentally restrict its use. Furthering our understanding of shockwave therapy can only bring clarity to this dialogue.

We know, for example, that the analgesic effect that comes with a treatment wears off after about three days. But do we know exactly how and why shockwave therapy appears beneficial in the treatment of certain injuries? Not quite. What's more, there had been little to no empirical data to determine whether shockwave treatments are associated with a higher risk of catastrophic injury in racehorses, as some fear.

A recent study that Tim Parkin, a University of Glasgow professor of veterinary epidemiology, conducted for racing officials seeking to learn more about the practice offers important insights into just that, however.

Working with these officials and using the Equine Injury Database (EID), Parkin looked at horses that had been reported on the vet's list for shockwave treatment, then counted the number of days and races since the treatment before that horse was fatally injured. Parkin found it”statistically significant” that horses that received shockwave therapy in the last 90 days, 180 days, and ever were between 54% and 79% more likely to suffer a fatal injury than horses that had never received such treatments.

For horses that received shockwave therapy in the last 30 and 60 days, the risk of fatal injury was also elevated: 26% and 65%, percent respectively, but these numbers (due to small numbers of horses treated so close to a race day) were not statistically significant.

The confidential study–conducted for research purposes and not published in any peer-reviewed journal–isn't definitive proof that shockwave therapy is a single factor predisposing horses to a greater likelihood of fatal injury. For example, the locations of the shockwave treatments weren't identified in the data–an important point if causal links are to be made between treatments and the site of the fatal injury (more on this later in the story).

The numbers do suggest, however, that there might be a correlation between underlying physical issues that necessitate shockwave treatments and a higher prevalence for catastrophic breakdown, said Parkin.

“Essentially, the pathology that drove the use of shockwave or drove the use of getting on the vet's list remains–at least the impact of that in terms of risk of injury is retained in that horse for the rest of its racing career,” said Parkin.

“It may drop off a little bit,” he added. “But however far away you go from the vet's list listing, or the shockwave use, then the horse is still at greater risk than before the vet listing of shockwave treatment.”

What is shockwave therapy?

In summary, a shockwave machine works like this: it emits sound waves (that resemble loud cracks) in doses that can be increased and decreased, depending on the severity of the injury. Treatments usually are delivered multiple times over a series of weeks.

How do these sound waves hasten and promote the healing process? Studies on humans and animals show that they trigger an anti-inflammatory response within the body and promote the growth of new blood vessels, among other effects.

Nevertheless, exactly how it works on racehorses is still open to debate.

Generally, veterinarians who use the machine say that it's most effective on concussive injuries in racehorses like suspensory problems, sore shins, tendonitis, and sacroiliac issues. According to French-born trainer Leonard Powell, it's used in France to treat back problems with greater frequency than in the U.S.

“The rider will spend a lot more time on their back in France,” explained Powell. “The riders are a bit heavier over there, too.”

When it comes to the analgesic effects from shockwave application, the scientific consensus is that it lasts between two to three days after treatment. One 2004 study found that analgesia could last up to 35 days after treatment, but experts argue the parameters of that particular study aren't relevant to the way shockwave treatments are administered to horses.

Most jurisdictions follow either in full or in part the Association of Racing Commissioners International's model rule on shockwave usage. This includes requirements that shockwave machines are registered with a commission and used only by licensed veterinarians in designated locations, as well as how horses given a treatment are placed on a vet's list and prevented from racing or breeze for at least 10 days.

However, while most jurisdictions are strict about who can use the machine, fewer of them require shockwave therapy to be performed at specific locations at a licensed facility, which, when factored alongside the current absence of any way to test whether a horse has received a shockwave treatment or not, leads vets and others to this central worry:

Without adequate oversight, the machine could be used on a horse to numb the pain of an injury before a workout or race.

This fear is why Mary Scollay, the newly minted Racing Medication and Testing Consortium executive director and chief operating officer, is concerned about the movement of horses to locations that fall outside the jurisdiction of a racing commission. “It defies regulation in Kentucky” as a result of that, said Scollay, the state's former equine medical director.

“I have a real reluctance to write rules that can't be enforced,” she added. “I think that constrains the people who would do the right thing anyway and empowers the people who make poor decisions.”

Because of these reporting holes, Scollay said she's unable to gauge the full extent of shockwave use in Kentucky. As an example of how prodigiously shockwave is used elsewhere, there were 143 individual shockwave treatments during this summer's Del Mar meet.

At the same time, there are those, like Ryan Carpenter, a practicing veterinarian in Southern California, who regard shockwave therapy as a legitimate veterinary practice when used within the rules and with necessary caution.

“It's got a bad name and people automatically assume that it's a bad thing, and it's not,” said Carpenter. “All the science supports the way we use it as safe and effective, and to arbitrarily remove it because you don't understand it makes no sense to me.”

In 2017, Carpenter and Jeff Blea, current chair of the American Association of Equine Practitioners' Racing Committee, co-authored a report on shockwave therapy for the CHRB when it last considered a shockwave rule change. The report's findings didn't call for further tightening of the rules, and indeed the proposed change was quashed.

The way in which Carpenter uses shockwave, he said, has become more conservative with time, and his methodology before a treatment typically looks like this.

The day after a horse works, Carpenter will evaluate it using one or more of a variety of tools, including nerve blocks, radiographs, ultra-sound, and nuclear scintigraphy. If, during the evaluation, the horse is shown to have a problem in something like its upper suspensory, “that's a perfect candidate for shockwave, and that horse benefits for that procedure,” said Carpenter, who added that the horse will then be placed on a regime of light work–just walking, jogging or slow galloping.

He said he couldn't remember the last time he administered shockwave treatment to a horse 10 days before a run, as the current rules permit. Nonetheless, he agrees with Scollay that strict policing of the procedure is vital.

“You could, if you were somewhere away from here, shockwave a horse the day of a race, put it on the van,” he said. “There's no way to test for it. So, a lot of it is the honor system.”

“It's unlikely any individual horse has pathology at a single site”

Which brings us back to the study Parkin recently conducted, and the import of his findings. Carpenter said that about 90% of the shockwave treatments he conducts are to the high suspensory and to the shin.

“Catastrophic breakdowns related to shins and high suspensory [injuries] are essentially non-existent. The thing we worry about in the racehorse is the fetlock,” Carpenter said.

“We're not shockwaving the areas where they have catastrophic injuries,” Carpenter added. “You can't say, 'because the horse was shockwaved that's the reason why they broke down.' Look at the diagnosis–what was going on? Was there a misdiagnosis?”

During her time as Kentucky's equine medical director, Scollay was aware of only one instance of a horse fatally injured after receiving a recent shockwave treatment, and the physical site of the treatment didn't match the site of the breakdown, she confirmed.

Nevertheless, Scollay wouldn't be surprised “if there is a correlation between a site being treated and subsequent failure,” she said, adding that it 'ties in' with current understanding of pre-existing diseases, and the accumulation of damage over time.

On top of that, there remain lingering questions about exactly why shockwave is an effective technology, and the specific biological responses triggered via a treatment. Which leads to what she calls the bigger question:

“Is there a correlation between shockwave treatment and fatal injury at a different site?” she said. “Does the shockwave cause the systemic release of a locally released mediator that can exert effects elsewhere in the body—potentially increasing risk at other sites of bone injury?”

Parkin said he agreed that the area of the shockwave treatment doesn't necessarily tally up with the site of a catastrophic breakdown. Rather, he emphasized how the treatment, and the horse's inclusion on the vet's list, is an indicator of elevated risk of catastrophic injury–that the horse is probably lame, likely suffers pathology of some kind, and needs treatment.

“It's unlikely any individual horse has pathology at a single site,” he added.

Which explains why this kind of information is “an extra bit of kit in the kit bag” for regulators to use as a screening tool, Parkin said. “The more information we get, the better we can be at predicting true risk before a race.”

The trick, Parkin added, is that the information given regulators is as granular and specific as possible. “At the moment we have quite a lot of uncertainty about all of these risk profiles, but the more detail we have about exactly what the horses have experienced, that risk will only be more precise,” he said.

“There are tons and tons of things that we would love to get a handle on,” he added. “We'd like to look at the whole history of the horse in terms of veterinary records, everything that's gone wrong with them. You'd be pretty sure lots of those things would each contribute some level of risk to the individual animal.”

Right now, Parkin is widening the net. He and his researchers are currently coding about 150 million data points over a 10-year period using as many as 50 different variables–things like work data, races, and shockwave use. Alone, some 3 1/2 million individual starts have been inputted, said Parkin.

“The code is running one week at a time to generate new variables,” he said.

From that large national database, Parkin will then be able to zero in on regional jurisdictions, build an individual model for specifics tracks, to see whether things like shockwave usage represent a significant risk or not in that peculiar location–

something he's currently doing for Southern California.

“We may see an elevated risk through shockwave in Southern California or it may disappear altogether because it's accounted for by other things,” he said, adding that he hopes to have results prior to the Breeders' Cup this year.

“Racing is so different from north to east to south to west,” he said. “We genuinely don't know what we're going to find.”