Shock Wave Therapy Looks Promising

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The equine athlete diagnosed with navicular disease, high suspensory ligament problems, osteoarthritis or bucked shins faces an uncertain future, since the results of the common treatments for these problems are often unsatisfactory.

Extracorporeal shock wave therapy (ESWT), commonly used in human medicine to break up kidney stones and help problem fractures to heal, shows promise for these problems and more in equine care. Until recently, however, there has been no research exploring its uses and effectiveness in horses, and many practitioners have been hesitant to use it.

Recently, two researchers presented preliminary results of their work with ESWT at the Association for Equine Sports Medicine annual meeting. The researchers, Dr. Scott McClure of Purdue University and Dr. Brad Scheuch of the University of California, Davis, reported success with ESWT on horses with a variety of lower limb problems. (For results, see box “Shock Wave Applied.”)

McClure presented a research update and discussed clinical applications of ESWT. “When people hear ‘shock wave therapy,’ they think they will see the lights go dim in the Midwest because we’re running a lot of electricity through the horse,” McClure said. “That’s not the case.”

Instead, the shock waves affect a very small area of the horse. “It’s a very thin wave of pressure running through the tissue or fluid,” he said.

The waves result from an electromagnetic pulse, or electricity run between two electrodes. “This reaches very high pressure in a short period of time,” McClure said. The pressure, which is measured in megapascals, may reach 60 to 65 in just 15 to 20 seconds, or 100 times atmospheric pressure.

If the shock wave is sent through water or fat, 99 percent of the wave’s energy is transmitted. If muscle and/or bone are the target, 65 percent of the wave’s energy is transmitted.

“You can damage tissue if you try to deliver a shock wave through an air interface,” McClure said. “Ninety nine percent of the energy is reflected then, and that’s not good.”

McClure noted that when a shock wave is sent through fluid, it causes small bubbles to form. The next shock wave compresses the bubbles, which then implode and send out rapid shock waves of their own, causing “fast fluid flows.”

So what happens when a shockwave is directed through tissue? “We really don’t know,” said McClure.

Studies have shown, however, that ESWT increases bone density and has been used in humans for treating “non-unions,” or fractures that don’t heal, tennis elbow, heel spurs and to loosen implants that have been cemented in.

In his study, McClure and his colleagues evaluated the acute effects of ESWT on the metacarpus (cannon bone of the forelegs) and metatarsus (cannon bone of the hindlegs) of four sound geldings. The horses ranged in age from three to seven years old and in radiographs had normal metacarpus and metatarsus bones.

With the horses under anesthesia, one metacarpus was treated with 1,000 pulses from an electrohydraulic generator at an energy of 0.89 millijoules (mJ0/mm2) to the dorsal aspect of the middle of the bone. The opposite limb was the non-treated control.

One metatarsus was treated the same as the metacarpus and the opposite at the maximum energy of 1.80 mJ/mm2 for 1,000 pulses. The horses were euthanized before recovery from anesthesia.

“We gave one dose of shock therapy. . . and the horse was back into training in 110 days.”

“We didn’t find any microfractures,” McClure said. “We did get redness on some bone,” he said. The redness appeared on the outer surface and, when the bone was cut into sections, was found on the inner surface as well. Also, under microscopic examination, it appeared as if cavitation bubbles had formed in the bone.

“They normally don’t last, but here they seem to have,” he said, pointing to a slide of the bone section. “It looks like the shock waves have done some damage to the bone.”

The researchers found that the red blood cells in the bone had burst, but that the osteoblasts, or the cells that form bone tissue, had remained intact. The treatment was repeated on two quarter horse geldings. These horses were given tetracycline 14 and 28 days post treatment. Tetracycline is taken up by osteoblasts and leaves a fluorescent mark showing new bone growth. On day 30, the horses were euthanized. “We found notably increased bone formation in these horses,” he said.

McClure, S et al. Extracorporeal shock wave therapy for equine musculoskeletal disease: research update and clinical applications. AESM Annual Meeting Proceedings, September 2000.

This article and sidebar originally appeared in the October 2000 edition of International Equine Science: (802) 888-6189.

Shock Wave Applied

Dr. Brad Scheuch, of the University of California, Davis, re­ported preliminary results of a study using extracorporeal shock wave therapy (ESWT) on 67 horses brought into the clinic for a variety of bone and joint disorders. The researchers wanted to see which lesions would be affected and how they would be affected over time, Scheuch said.

All horses were treated standing, and the focal point of treatment was about the size of a dime. Ages of the horses treated ranged from two to 21 years, with a mean age of nine years. The horses were treated on an out-patient basis.

“Most horses tolerate treatment fairly well while heavily sedated,” he said. Follow-up evaluation was requested at 60 to 90 days post-treatment.

“We’re on a bit of a fishing expedition right now figuring out which cases we want to treat,” he said. That means the researchers examine many horses that are rejected. These horses can be used to provide controls, he said. “We’ll get our controls by doing a retrospective look at horses considered for treatment,” he said.

Thirty-four of the cases were treated for primary bone and joint lesions, accounting for a total of 49 lesions. Twenty-two stress fractures, two non-union fractures and one avulsion fracture (when a ligament or tendon pulls a fragment of bone off) of the sesamoid bone of the right forelimb were treated.

There were five degenerative osteoarthritis cases: three in the pastern, one elbow and one of the lower hindleg. Six navicular syndromes were treated and one exostosis, or growth of bone on the right forelimb cannon bone.

One horse treated for a humeral stress fracture, or a fracture of the bone that links the scapula of the shoulder to the upper foreleg, showed dramatic improvement, Scheuch said.

“This was kind of an exciting case,” Scheuch said. “We gave one dose of shock therapy, reevaluated in 90 days, and the horse was back into training in 110 days.”

Another horse with osteoarthritis in the pastern showed “a remarkable...response,” he said. Of three horses treated for navicular disease, one significantly improved its lameness score and is presently sound.

Of 26 horses treated for suspensory ligament desmitis, eight have completed the 90-day follow-up exam. Seven of these cases have improved their lameness scores and/or returned to work. Ultra­sonographic examination showed improvement in five of these cases.

The horses with bucked shins showed significant improvement as well, Scheuch said. “They’re cold and they’re happy in 10 days,” he said. “They’re happy, I think, because of the therapy.”

Overall, the preliminary results of the study suggest ESWT is an effective treatment for chronic suspensory ligament lesions and metacarpal stress fractures, according to the researchers. In addition, ESWT shows “very few” adverse side effects. [sm]

Scheuch, B et al. Clinical evaluation of high-energy extracorporeal shock waves on equine orthopedic injuries. AESM Annual Meeting Proceedings, September 2000.