Take a lame horse, inject him with stem cells or cells from a pig's bladder lining, zap him with extracorporeal shock waves, and what do you get? That's just one of several research projects involving extracorporeal shock wave therapy (ESWT) that are underway or have been recently completed. Following are reports of some recent research using ESWT to help you work with your veterinarian to decide if this treatment is right for your horse.

Refresher Course

"ESWT utilizes high-pressure sound waves focused at a very small, specific site within the body to aid healing of muscular, tendon, and bone conditions," explains Scott McClure, DVM, PhD (veterinary physiology), Dipl. ACVS, assistant professor in the Department of Veterinary Clinical Sciences at Iowa State University.

Based on the same technology whereby lithotripsy breaks up kidney stones in humans, ESWT has been applied in horses to stimulate blood flow and bone remodeling, and to repair ligaments. "The pressure waves can be focused at tissue within the body; the tissue between the surface and focal point is not affected," McClure says.

Having studied and used ESWT in equines since 1999 (including on Olympic team horses), Jack Snyder, DVM, PhD, Dipl. ACVS, chief of equine lameness and surgery and professor at the University of California, Davis, reports that ESWT can hasten healing, although not beyond the ideal healing time. "For a wound that doesn't heal or heals slowly," he says, "ESWT could speed up healing to--but not beyond--the point where the wound would totally and normally heal in a normal situation. ESWT improves the healing of injuries that, in many cases, would not heal."

He says ESWT appears to work best on ligament injuries, and to some degree on some tendon injuries and on stress fractures of the cannon bone. Additionally, ESWT has been reported to bring pain relief for a few days (more on this in a moment).

However, for ESWT to be used appropriately, answers are still needed. Notes Christopher Byron, DVM, Dipl. ACVS, an assistant professor of equine surgery at the University of Illinois, "ESWT seems to have a place in the treatment of some diseases, but is still a fairly new therapy. Further research is needed to determine what diseases can be helped by ESWT, how it should be best applied, and to establish the safety of the treatment."

Pain Relief Unmasked

There is continuing examination of ESWT's analgesic (pain-killing) effects.

In studies done at Iowa State University, McClure found that ESWT produced an analgesic effect of about three days duration. "This is important, primarily for racehorses," he says, "where you wouldn't want them performing without the full recognition of pain. Currently, we're still concerned about some of the analgesic effects and potential associated risks and are trying to gain more information in this area."

Similarly, Jeremy Hubert, BVSc, MRCVS, MS, Dipl. ACVS, assistant professor of equine surgery at Louisiana State University, and his colleagues have investigated shock wave effects on nerves. "We found there probably is a degree of nerve damage to the extent that they probably don't have normal sensation, which could explain why those horses feel more comfortable after a treatment. Damage to nerves is usually transient; although we didn't evaluate the effects beyond 30 days, based upon our knowledge, it might last longer than that," he says.

In a recently completed study involving navicular cases, Byron found lameness in horses undergoing ESWT treatment averaged improvement of about one lameness grade. Horses received one ESWT treatment every week for three weeks starting two weeks after receiving corrective farriery to resolve ongoing foot problems (poor hoof balance, long toes, poor hoof angles, etc.).

"We will be looking further at navicular disease cases to see if ESWT changes the appearance of the navicular area on imaging (such as radiographs)," he says. "This will hopefully help us determine how ESWT may be helping these patients and will give us a better idea of what we can expect long-term, after the treatment series has stopped."

Helping Healing

The other major area of interest involves ESWT's role in improving or increasing the speed of healing.

Studies of ESWT for suspensory ligament problems continue to yield positive results. In an unpublished review of cases, Olga Seco, MRCVS, a staff veterinarian focusing on sports medicine and imaging at the University of Pennsylvania's New Bolton Center, followed horses with suspensory ligament desmitis treated with ESWT. The horses received three ESWT treatments of 2,000 shocks at three-week intervals for a variable period of six months to more than two years.

"Eighty-five percent of horses with a longer follow-up became sound and returned to full work," she says, 82% of those at the same level, 17% at a lower level. Results from horses still returning to exercise were similar. "Horses with injuries in the front legs had a better outcome than the ones affected in the hind legs; outcomes were similar for acute and chronic injuries."

Currently evaluating ESWT's role in suspensory ligament healing is Rich Redding, DVM, Dipl. ACVS, clinical associate professor of equine surgery at North Carolina State University. He is using MRI exams to study suspensory ligament injuries.

"Once we have looked at enough normals and abnormals to define patterns of injury seen with MRI, we want to look at different treatment modalities' effects on healing, again using MRI."

At UC Davis, Snyder is evaluating the effectiveness of ESWT used in conjunction with injections of either stem cells or Acell (tissue matrix from pig bladder lining) in healing ligament injuries. "We're also comparing these two compounds in a group of horses that either get re-injured or they don't heal," he says.

Also being evaluated is ESWT's effect on joint cartilage. Performed on cartilage tissue in the laboratory (results might not directly reflect what could be happening clinically), Byron found that while the structure of the tissue was unchanged, there was a very small degree of cartilage cell death.

"We used energy levels higher than the cartilage would probably see clinically in most cases, so how this relates to the clinical situation remains to be seen," notes Byron. "We are planning to follow up by looking at other parameters to determine other ways in which shock waves might influence cartilage cells. This research will give us a good knowledge base as to what might be happening when ESWT is used around joints. Future work will help determine what the safe limits are when ESWT is used to treat diseases in and around joints."

The effect on bone is likewise under scrutiny. Using normal horses, Mauro Verna, DVM, a resident in large animal surgery at the University of Minnesota, applied non-focused ESWT to see if bone remodeling occurred. "We wanted to observe the reaction of the normal bone, then in the future work with abnormal bone to evaluate any changes that ESWT may induce," he says. Bone scans (nuclear scintigraphy, which shows bone remodeling) revealed no changes after four treatments.

In a separate study, LSU researchers used scintigraphy to evaluate whether bone dynamics changed immediately after shock wave treatment on normal legs. "We haven't finished the data," Hubert reports, "but it appears there aren't any changes in bone early on. We don't really know what this indicates yet; however, it could mean that ESWT doesn't cause any damage to the bone or that it was too early to see any changes."

Hubert is also investigating whether ESWT hastens or slows repair in healing bone. "We drilled a hole in the bone of one leg and a hole in the bone of the other; one leg we shocked, the other leg was not. Although the study is still incomplete, it appears that ESWT doesn't have much effect on the rate of healing in normal bone."

Additional studies that are underway or soon to be launched include the following:

* Alison J. Morton, DVM, MSpVM, Dipl. ACVS, assistant professor of large animal surgery at the University of Florida, plans to evaluate horses with injuries to the collateral ligaments of coffin joints or to the distal sesamoidean ligaments to see if ESWT benefits these horses compared to horses that didn't receive ESWT. "I'll evaluate speed of healing, ultrasonographic appearance of healing, duration of recovery, return to previous level of soundness and performance, and incidence of recovery," she says.

* Snyder is presently categorizing horses, the type of injuries they have, and how well ESWT helped them heal.

Further Thoughts

Although ESWT has already demonstrated its effectiveness in treating particular disorders and holds the potential for addressing other musculoskeletal problems, veterinarians warn that one should not drag out the shock wave machine and use a willy-nilly approach at the first sign of lameness.

Says Redding, "I cannot emphasize enough the need to accurately diagnose the problem before initiating treatment. If inappropriately applied--for example, using the recommended higher-energy settings for treating a presumed bone injury when the disorder is actually a soft tissue injury (requiring reduced energy settings)--shock wave could be harmful to the repair process. Acute injuries are also treated with lower settings than chronic injuries, so knowing the stage of the injury is also important. Much more research needs to be performed to guide the practitioner in application."

Additionally, the therapeutic levels of energy used and the frequency of application for soft and hard tissue injuries still need to be better defined. Notes Hubert, "It's pertinent to do more research to determine exactly what's happening, to develop better guidelines relating to the amount of energy that's being released and how many shocks to give. There are no controlled studies regarding how much energy should be used; it would seem obvious if there is too much energy, there is potential to damage the targeted cells. At the moment, it's relatively anecdotal, and we're just basing our treatments on manufacturer recommendations."

Fortunately, with interest in ESWT remaining high, those and other answers based on sound research should soon become a reality.

Shock Wave Therapy Applications

Jack Snyder, DVM, PhD, Dipl. ACVS, chief of equine lameness and surgery and professor at the University of California, Davis, and Alison J. Morton, DVM, MSpVM, Dipl. ACVS, assistant professor of large animal surgery at the University of Florida Veterinary Medical Center, are among those practitioners who have utilized ESWT in their practices. Here's what they've found:

Ligaments--"Shock wave therapy appears to work best on ligament injuries," Snyder says, "especially where ligament attaches to bone." Snyder usually prescribes ESWT along with local therapies such as hydrotherapy, ice, and/or direct electrical stimulation or transcutaneous (through skin) electrical stimulation.

"The difference between a healing point of view is if I don't use shock wave, I start rechecking the horse at about 60 days with ultrasound; with shock wave, if I'm really pushing, I'll re-evaluate the injury in 35-40 days," Snyder says. When using shock wave, Snyder introduces exercises earlier, backing off if the horse displays any lameness. "We also use a force plate system (to measure the amount of weight a horse places on the leg) to objectively make sure the horse is putting the normal weight or the same weight on the injured leg."

In general, for soft tissue injuries, Snyder gives three shock wave treatments spread out over two or three weeks and one or two treatments for bone injuries.

Acute and chronic flexor tendon or ligament injuries--"In combination with ESWT, I incorporate a strict regime of controlled exercise (stall rest with gradually increasing hand walking), anti-inflammatory therapy (local cold hosing, bandaging, etc., and systemic phenylbutazone or similar medication), and polysulfated glycosaminoglycans (such as Adequan) therapy," says Morton. "In my opinion, horses heal much more quickly, with a better ultrasonographic quality of healing, and return to performance in a more timely fashion after an appropriate course of ESWT."

Acute and chronic injuries to the ligaments of the back and pelvis (supraspinous ligaments, dorsal sacral iliac ligaments)--"I handle these cases identically to tendon and ligament injuries, except for in horses with acute pelvic injuries such as subluxations or bony asymmetries," Morton states. "With these horses, I have a veterinary chiropractor evaluate and treat these conditions, and also incorporate a 'back exercise program' that strengthens the musculature that supports the pelvis. I incorporate the back exercise program for all the back and pelvic injuries, including the ligament injuries."

Acute and chronic back muscle pain--after identifying and using appropriate therapies specific to the underlying cause of back soreness, Morton sometimes uses ESWT. "I believe this makes these horses more comfortable quickly, but the effect seems short-lived, in most cases."

Chronic osteoarthritis of distal hock joints, pastern joints, and sacroiliac joints of the back--"I have used ESWT for horses that were refractory to other treatments (joint injections, rest, anti-inflammatory therapy, acupuncture, etc.)," Morton reports. "My overall impression is that ESWT is not that helpful and should only be used if other modalities have failed."

Acute or chronic fractures of splint bones and coffin bones--"I've administered shock wave on a handful of cases to augment other therapies, and believe ESWT is not particularly helpful for enhancing fracture healing in these bones," Morton says.

Navicular syndrome--"Using ESWT on a handful of horses with refractory navicular pain, I found ESWT is similarly beneficial as seen with chronic arthritis horses: I believe it can provide a very transient improvement in lameness," says Morton.

Using a focused unit, Morton administers three shock wave treatments two to three weeks apart for soft tissue problems, three treatments for fractures also two to three weeks apart, and multiple, as-needed treatments for horses with osteoarthritis of distal hocks and pasterns, but no more often than every three weeks.--Marcia King

About the Author

Marcia King

Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She's schooled in hunt seat, dressage, and Western pleasure.

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