A lot of improvements have occurred since McCarroll started to do these treatments in the late 1990s. As the first veterinarian
to use the procedure, he didn't have a machine that would allow him to apply the treatment to a standing horse. They had to
anesthetize the horse to get him in the proper position to deliver the treatment. The fact that there is miniaturization of
the equipment now allows veterinarians to be more flexible.
"The machine that I use generates a charge with an electrode," says Van Snow, DVM for Santa Lucia Farm in Santa Ynez, Calif.
"The wave is very powerful and the procedure very painful, so we have to use general anesthesia when we use it with the horses
in lateral recumbency."
If Snow is treating the navicular bone, it requires that the frog be paired down to near bleeding so there is enough moisture
in the foot to conduct the wave well. He treats with 2,000 impulses (on a power setting of "7") through a window in the frog,
in the area where one would do a "street-nail" procedure. He also treats through the bulb of the heel, as if to inject the
navicular bursa, at 1,000 impulses. He commonly treats both feet.
"Treatment is critical to the proper location, target specific," McCarroll says. "The more accurate you can be locating exactly
where the pain is originating, the more successful it can be. Second, you need to use a very high-energy level of shock wave,
and you need to use enough of it to make a difference."
A small, defined area requires fewer impulses than a larger surface area. The more shallow and softer the tissue, fewer and
milder impulses are required; the deeper and harder the tissue, the greater the number of impulses and energy required.
His usual treatment regimen is to use the high end of the treatment level, which is normally 1-1.1 millijoules per mm, delivered
at about 2,000-3,000 times per site.
"Using high energy levels at one time is better than repeating smaller energy levels at a lower frequency," McCarroll suggests.
"I think you can do a lot better by doing one great big treatment."
Horses do better post treatment when rested. According to McCarroll, after ESWT, the pain subsides, and the horses heal usually
within one to four weeks, depending a lot on the chronicity of the problem and area of involvement.
"I don't think you need to retreat, to treat them frequently. I don't think that is a good idea," McCarroll cautions. By giving
enough of them to stimulate a dramatic healing response, I think the horses do better."
Though the mechanism of action is unsubstantiated, McCarroll says shock wave therapy might promote production of proteins
and enzymes that are involved in the stimulation of bone healing. Shock wave therapy is most beneficial at the soft tissue/bone
interface, such as a tendon insertion or a ligamentous attachment to bone.
Uses and Results
"It is a fairly safe technique, I'm using it to try to stimulate healing," says Duane Rodgerson, DVM, Hagyard-Davidson-McGee
in Lexington, Ky.
He's tried it on various conditions, including bone cysts, pasterns, fetlocks, the distal cannon bone, some tendons and suspensories.