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Scott McClure, DVM, PhD, an assistant professor in the Department of Veterinary Clinical Sciences at Iowa State University, has been at the helm of much of the shock wave therapy research performed in horses over the past five years. At HMT's third annual extracorporeal shock wave therapy (ESWT) symposium, held in Denver, Colo., on Dec. 3, McClure highlighted some of what veterinarians have learned in the past year in ESWT treatment in the areas of analgesia and the modality's effect on nerves and soft tissue.
Much of what equine practitioners are learning about ESWT is coming from veterinarians using the modality in the field. "Keep track of what you're doing (with ESWT)," said McClure. "We learn as we go, and everyone can contribute to these meetings in the future."
Analgesia
In ongoing forceplate studies, McClure says that he is "not seeing a huge amount of analgesia" provided by ESWT, and that any analgesic effect is back to baseline within three days. "We're treating the navicular bone, not nerves. (The effect) is not anywhere close to a blocked horse." Still, there is controversy when it comes to regulating the treatment and the racing regulators and show horse officials are monitoring the situation.
Nerves
McClure reviewed research in rats showing that shock wave application to rat skin induced degeneration and re-innervation of sensory nerve fibers, as evidenced by immunohistochemical staining of skin and periosteum. The plantar pads of the rats were given 1,000 pulses or "shocks" at a power level consistent with what would be used in the horse. Epidermal nerve fibers in ESWT-treated skin degenerated almost completely, but re-innervated.
"We're looking at this in horses because it is getting down to something we can statistically measure," said McClure, "and we can answer some of these questions (about the effects of ESWT on nerves)."
Soft Tissue
Additionally, McClure mentioned the presentation (given Dec. 7 at the 2004 AAEP Convention in Denver) of a surgery resident at Iowa State, Kevin Kersh, DVM, who studied the effects of ESWT on collagenase-induced superficial digital flexor tendonitis. He found that horses had a more significant capillary ingrowth in the treated tendon 85 days post-treatment.
A study on the effects of ESWT in collagenase-induced patella tendinopathy in rabbits showed a 10% increase in tensile strength of the tendon at 16 weeks post treatment. The histology showed that there was an increase in tenocytes (tendon cells), neovascularization, and hydroxyproline content (indicating improved tendon fiber healing).
Similarly, a study in canine Achilles tendon-bone junctions showed new capillary and muscularized vessels at four to six weeks following ESWT treatment, and neovascularization (proliferation of blood vessels in tissue) of the bone tendon junction was evident.
Finally, McClure touched on his study that was presented at the AAEP convention on ESWT treatment of navicular syndrome. He found that two-thirds of horses with navicular disease improved an average of one grade of lameness following ESWT treatment.