As a boy growing up in New Zealand, C. Wayne McIlwraith, DMED, DVM, PhD, would ride his bicycle to a track marked out over a sheep pasture and watch the horse races. Although his parents thought that the rough-and-tumble contests had a bit of an unsavory tint, he was fascinated.
Dr. McIlwraith pursued his passion for horses, combining it with medicine and research to develop groundbreaking approaches in arthroscopic surgery and in the treatment of cartilage, bone, soft tissue injuries. From his post at Colorado State University (CSU), where he is a University Distinguished Professor and oversees the Equine Orthopaedic Research Center, he regularly travels to southern California as well as to Europe to treat racehorses.
Just as advances in arthroscopic surgery and other joint-repair procedures have enabled human athletes to return to competition after injuries that once would have permanently hobbled them, so are many Thoroughbreds able to return to the track rather than retire to the pasture, thanks to innovations achieved by Dr. McIlwraith and his colleagues in veterinary medicine. And although certain fracture and soft-tissue injuries still portend inevitably fatal outcomes for horses, progress is being made in repair techniques and postoperative therapy and rehabilitation.
“The biggest advances have been in arthroscopic surgery,” Dr. McIlwraith said. “We can remove fragments, treat meniscal tears, and perform internal repair of fractures all the way into the joint—and we can do it arthroscopically.”
A “close second” to the benefits brought by arthroscopy has been the development of better internal fixation techniques. “There is a crossover with arthroscopy,” he noted, “because with condylar fractures and slab fractures, we use screws under arthroscopic guidance rather than opening the joint up.”
The shared characteristics of the horse’s stifle and the human knee mean that the challenge of restoring damaged cartilage in a racehorse and a football player is similar. “We have a way to go in cartilage repair,” Dr. McIlwraith said. “Microfracture—although still the standard of care—is useful and has helped many human athletes, but it has limitations.”
He and his colleagues are focusing on biologic therapies that may yield better results than mechanical procedures. In this realm, treatment methods for horses may outshine those available for humans, in no small part due to regulatory divergencies. “For horses we are pretty flexible in what we can do, but in humans we face more restrictive regulations,” Dr. McIlwraith said.
Among the promising biologic agents being used and evaluated in horses are IRAP (interleukin-1 receptor antagonist protein therapy, also known as Orthokine®) and bone-marrow derived stem cells (BMDSCs)—neither of which is approved for human use in the United States.
Dr. McIlwraith said that, he’s seen promising results using stem cells used to treat injuries in Western cutting and reining horses, which are prone to trauma in the femorotibial joints. “Repair techniques are limited,” he said. “In the horse, we can do resection for grade 1 and 2 tears, but in grade 3, the tear ‘disappears’; we can’t get access to the whole tear.” In a paper currently in press, Dr. McIlwraith reports results that show “injecting 20 million BMDSCs into the joint can result in getting back 60 percent athletic soundness—versus zero without.”
That study was developed and led by David Frisbie, DVM, PhD, also of CSU; the idea came from “quite remarkable regrowth of meniscal tissue in goats,” Dr. McIlwraith said.
Regulatory restrictions and the reluctance of pharmaceutical companies to invest large sums in the sorts of trials that would be required to obtain approval for the use of stem cells in humans may be confining such advances to veterinary science. Dr. McIlwraith, an associate member of the Academy, recalled an orthopaedic colleague who observed, that “I can use a 15-year-old slide to show what is available for cartilage repair in humans,” but also noted that cross-pollination between veterinary and human medicine is occurring.
Although both branches are exploring the effectiveness of platelet-rich plasma (PRP), the results in humans and horses continue to be inconclusive. “In horses, we have used it quite a bit, including for acute tendon injury, but without not much proof of efficacy yet,” said Dr. McIlwraith. “We need a better definition of which product is best. With flexor tendon and suspensory ligament injuries, our study shows more success with stem cells. PRP possibly supports the therapeutic effect.”
He noted that the Food and Drug Administration (FDA) takes a more permissive stance in allowing use of PRP versus stem cells, due to its definition of “minimal manipulation.” Creating PRP is a rather simple process. “You are not manipulating anything,” said Dr. McIlwraith. “Stem cells have to be cultured. Bone marrow is spun down to isolate stem cells; then the stem cells are cultured, which is above the level of minimal manipulation.”
The well-known susceptibility of horses to devastating consequences from racetrack injuries remains a daunting hurdle for equine surgeons.
“The limitation is that our patients have to stand up after anesthesia,” Dr. McIlwraith said. “Upper limb fractures are challenging. Distal limb fractures can be protected in a cast, but may still involve so much soft-tissue injury and blood supply loss that avascular necrosis or osteomyelitis develops.”
Distal limb injuries can be especially grave in horses. “As with distal tibial fractures in humans, the problem is the blood supply,” Dr. McIlwraith said. “The horse doesn’t have a lot of blood supply in the distal limb. If an infection often develops, we can amputate in humans, but not in horses.”
Another lethal threat to the horse with limb injury is laminitis, which is what ultimately took the life of the Kentucky Derby winner Barbaro, who sustained multiple hind leg fractures during the Preakness Stakes in 2006. Although he seemed to be healing from the injuries, laminitis—an affliction in the hoof that occurs when excess weight is shifted to a noninjured limb—developed and led his owners to the difficult decision to euthanize.
“The big hurdle is that we have to get the horse weight-bearing on that [injured] limb,” Dr. McIlwraith said. “So we still lose many horses to laminitis, which can be triggered by a number of factors, including excess weight bearing, endotoxemia, stress, and a high level of carbohydrates. As the laminae break down, inflammation and necrosis cause it to come apart, and the distal phalanx (third phalanx or coffin bone) ends up rotating through the sole of the hoof,” he explained.
“These cases will make you cry. They break your heart. The good news is that we are saving horses that could not be saved before. Fracture repair has come a long way in 30 years,” he said.
Dr. McIlwraith—who received his veterinary degree from Massey University in New Zealand, continued his training in the United Kingdom and the United States, and has a PhD in arthritis research from Purdue University—finds many similarities between his equine cases and those his human orthopaedic surgery colleagues manage.
“We use a lot of the same equipment and we have to be relatively fast and efficient. Vets take out more fragments, and don’t want our patients on the table for too long. Equine patients risk mismatch of ventilation and perfusion of the lungs and can get muscle damage if they are down too long,” he noted.
“Surgical techniques are very similar, but afterward, horses are going to stand on their legs, without protection, unlike humans. The horse recovers in a padded stall and, if it was a fracture repair, will have an assisted recovery. Otherwise the animal gets up on its own,” he said.
In one area, humans have an advantage. “We are catching up with human aftercare,” noted Dr. McIlwraith. “Most of my patients do time on an underwater treadmill. They need exercise to reconstitute their bone mass and tissue strength. We start hand-walking them and put them into rehabilitation therapies.”
A troubled industry
Although Barbaro received excellent care, both as an active racehorse and after his breakdown on the track, his injury drew new scrutiny to the horse racing industry and its treatment of animals, especially those on the lower rungs. The industry, squeezed by vastly expanded gambling options, shifting public tastes, and numerous economic pressures, is foundering, and many question whether owners and trainers are misusing horses by running them too often, when they are unsound, or with the use of ill-advised or illegal medication.
“The racing model is a challenge,” Dr. McIlwraith admitted. “Many races involve journeymen horses that owners have to keep going. When racing was the only form of gambling, the tracks were full. With expanded gambling, only the big races fill the tracks. We have seen the golden days of horse racing.”
Yet Dr. McIlwraith still believes that racing can be conducted in a way that befits its sobriquet as the “Sport of Kings.” He would like to see a more unified and resolute system of regulation in the United States, replacing the current scattershot state-by-state approach and imposing a uniform standard for drug testing. The Racing Medication and Testing Consortium has been existence for 12 years with representatives from all parts of the industry and has achieved a considerable degree of uniformity among states with regard to medication, Dr. McIlwraith said.
“Ultimately horse racing will be a more selective industry with fewer tracks,” he said “We have to do right by the horses. I hate having to put a horse down. Most people in the industry want to look after the horse, but there are trainers who don’t care about the horses much.”
The love of racing and the animals that compete motivates Dr. McIlwraith to travel every other week to an equine facility by Los Alamitos Race Course in Orange County, Calif., and to other far-flung locales, where he operates on these four-legged athletes who are paid in oats and apples.
He and his wife, Nancy Goodman McIlwraith, a veterinarian herself whom he met while she was working at Los Alamitos 30 years ago, currently keep nine horses of their own. Dr. Goodman McIlwaith exhibits show hunter horses and assists her husband during surgery.
“These horses are great athletes,” Dr. McIlwraith said. “I like them a lot. They are great to work with. The ultimate reward is to see a horse have a pain-free existence and to see them come back to full competition.”
Terry Stanton is a senior science writer for AAOS Now. He can be reached at firstname.lastname@example.org