Prosthetics: Science, Not Science Fiction
There is a roadside pasture in Pullman, Wash., where a black Quarter Horse stallion has been known to stop traffic. It's not simply the pastoral beauty of a handsome horse in a natural setting that draws attention. Rather, it's that this particular stallion has a feature few people have ever seen on an equid: An artificial limb.
While hardly common, such sights have at least stepped out of the realm of wishful thinking and into the real world. Yes, it's a costly procedure. Yes, there are special considerations and potential complications. And, no, not every horse with a leg injury makes a good candidate. But through the efforts of dedicated, far-sighted veterinarians, farriers, and horse owners, equine prosthetics are viable options for giving some formerly doomed horses a new lease on a good life.
Thirty Years of Progress
Veterinarians have been applying artificial limbs to horses since at least 1970, when L.M. Koger, DVM, and colleagues fit a prosthesis to a horse's forelimb, says Barrie Grant, DVM, MS, Dipl. ACVS, co-owner of San Luis Rey Equine Center in California. The ensuing 30 years have seen considerable progress in prosthetic mechanics and materials, with modern devices borrowing from high-tech human medicine whenever possible, says Ric Redden, DVM, founder of the International Equine Podiatry Center in Versailles, Ky. That includes:
- Spring loading to improve shock absorption and help protect the leg stump;
- Form-fitted styling with a clamshell-style open/close mechanism; the limb is then secured in place with straps or clamp closures like those found on downhill ski boots, says Grant;
- Articulation, allowing a prosthetic to bend at a joint, so horses can more easily move, lie down, and get up;
- Advanced materials, progressing from iron and leather to lighter weight, durable molded plastics, often combined with fiberglass, stainless steel, or carbon graphite;
- Frog grafts developed by Redden that involve transplanting living frog from one of the horse's healthy hooves onto the end of the stump. This imparts toughness and resilience that increases the horse's comfort level, and might reduce sores and subsequent infections;
- Use of the pin cast technique to unload weight from the stump, thus alleviating post-operative pain. Redden, who pioneered this use of the process, explains that two stainless steel pins are placed through the distal cannon bone during amputation surgery. A cast is built around them, and the temporary prosthesis is fitted and secured to the cast. The horse wakes from surgery able to comfortably bear weight on the temporary prosthesis without putting pressure on the surgical site; and
- Slings to restrain and support a horse during post-op recovery from anesthesia, resulting in fewer fractures and other trauma linked to amputation surgery.
Future progress might be headed our way from Europe, says Donna Harper, DVM, a veterinarian in Roswell, N.M., who owns a horse with a prosthetic and has worked with Grant on prosthetics cases. For instance, she says, we could see prosthetics that attach directly to the bone, eliminating the device's socket, which is often the source of stump trouble.
Who's a Candidate?
Gideon's prosthesis was funded by the Cashvan Family Memorial Equine Fund, which is a 501(c)3 foundation providing a research base for equine amputations and prosthetics. Gideon is a Missouri Fox Trotter stallion standing at stud at Serenity Equine, an equine podiatry center; his fees go into the Fund. For more information on Gideon and this fund, click here.
PHOTO COURTESY DR. ANDREA FLOYD/SERENITY EQUINE
Despite progress, prosthetics aren't for every horse. The ideal candidate meets criteria related to injury type and site, health, and personality.
Injury type/site--Redden notes that an acutely injured animal that has lost blood supply to the foot is the preferred patient. "Circulation to the lower limb is the key," says Redden. "When there is adequate circulation there is much we can do, but when the circulation is gone, amputation is the only option."
Overall, though, Grant says the most common reasons for amputation include:
- Traumatic loss of limb below the knee or hock;
- Compound comminuted fractures of the distal limb;
- Septic arthritis; and
- Cellulitis in the distal limb that has not responded to aggressive therapy.
- Other injury-related points to consider:
- Hind limbs are preferable, since they bear less weight than forelimbs and usually let the horse retain a more normal gait.
- Amputations lower on the leg--but ideally no closer than six to eight inches from the ground--generally require less complex, and therefore less costly, prostheses. Not having the knee or hock encased in the device also allows the horse to lie down and rise more easily. Amputations above the knee or hock present a difficulty: Without the bulbous joint protrusion to provide a "catching" place, it's hard to keep the artificial limb in place. Redden has used a girdle-like harness for the purpose, but with limited success. Vacuum or pneumonic-style devices that work well in humans aren't effective for horses, says Redden.
- A horse crippled from an injury or disease that occurred months or years earlier, who is healthy and has learned to adapt to the disability, is not a candidate. "If the horse is happy, we don't take the leg off just to try and make him happier," Redden explains.
Health--A horse who, beyond the damaged limb, is in sound health makes a far more promising patient than one who is ill. Likewise, since the most common cause for euthanasia in horses with a prosthesis is failure of the supporting limb. If that leg is already compromised, the horse is not a good candidate, says Grant.
Personality--The patient's temperament can literally make a life or death difference. Grant says the horse must be tolerant of handling--including intense veterinary attention--and able to adapt readily to changing situations, including not only the loss of a limb and replacement with a prosthesis, but also a prolonged stay in the veterinary hospital and use of a sling. A horse that has adapted to the injured limb makes a promising candidate.
Harper believes that allowing horses more time to make that mental adjustment before complicating things with the prosthesis would be beneficial, resulting in fewer cases where the horse "freaks out" on waking from surgery, sometimes causing further damage. However, Redden says he has never experienced this problem.
"If we give the horse a couple of weeks, even a month, to figure out that the leg no longer works, then Nature will help them adapt," she says. "Once this mental change takes place, you can take off the leg and things go fine." Yet Redden warns that the chances of developing contralateral limb laminitis increase when the horse must bear all of its weight on the unaffected limb.
As one example, Harper notes that her mare had a month before amputation and was well adapted. "When she actually lost the foot, it was nothing new because she already knew she couldn't use it," she says.
Harper acknowledges concerns regarding infection or complications during the adaptation period. "But I personally believe that these issues can be addressed in many patients, and that the results are well worth the additional effort," she says.
To Complicate Matters...
Even for the ideal candidate, Redden says, "You can expect complications." These include pressure sores and overall difficulties with amputation-site healing. Long-term infection prior to amputation can linger or recur even after surgery; this can also weaken the limb's entire bone structure, potentially causing fractures of the bones above the prosthesis.
Also, says Redden, "You have to look after the opposite foot as much as the stump."
To combat the threat of contralateral (supporting) limb laminitis, for instance, he designed a therapeutic support shoe that reduces loading stress on the laminae, enhancing blood supply to the sole corium.
Owners must take other factors into consideration before moving forward with an amputation and prosthesis. These include the risks of general anesthesia, which patients undergo at least once. In addition, the horse is hospitalized for an extended period. Grant's prosthesis patients average a minimum stay of two months. Redden notes an average of four to five months for a complication-free procedure, allowing time for the frog graft and stump to mature and for the horse to become comfortable with the prosthesis. In addition, says Redden, if serious complications occur, it's typically within the first five months, and they're much easier to deal with at the clinic.
With this lengthy hospitalization, plus surgeries and the prosthesis, costs escalate quickly. The average tab runs from $10,000 to $20,000, but can top $80,000 with complications and hospital stays that can stretch to 18 months. Horses that do well with their new limb will also need replacement limbs (at a cost of about $5,000 each) probably every two to three years--more frequently for a young, growing horse.
For valuable brood stock, owners can often recoup the expense through stud fees or future foals, especially since many registries now allow embryo transfers and registration of multiple foals from a single mare in a year. But Redden discourages people from borrowing money or tapping out their reserves to pay for the procedure.
"You're dealing with a bad situation, not getting rid of a problem," he explains. "There will always be a problem to some degree. But it likely can be managed with adequate financial resources and the right personnel."
To encourage more owners to try the procedure, Harper and Grant would like to see equine mortality policies changed. Instead of only paying out when a horse is euthanatized following catastrophic limb injury, they'd like a clause that would pay the owner 75% of the payout to keep the horse alive. (Plus, the owner would get money from any future stud fees or foals.) The insurance company would keep 5%, and the vets would get 20% to go toward the surgery, explains Harper. "We just need someone to promote and sell the concept," she says.
A Question of Commitment
A last consideration, but hardly the least, is the intensity of commitment an owner must make to a horse with a prosthesis. "You have to provide care (for the horse) like for a parent in a nursing home," says Grant. "You need to be out there checking them every day. If you're not willing to do that, it's not fair to keep the horse alive."
Beyond close daily observation for signs of trouble, the owner also must remove the prosthesis, clean the stump, and replace the prosthesis at least once a week and in some cases every other day. And if the horse has received a frog graft, then the frog will need regular trimming, since it will continue to grow just like a normal frog. In some cases, the horse might require medication for an extended period or even life.
And of course, the horse can't be ridden again. "The owner's only expectation should be a horse that can breed or conceive, deliver, and nurse a healthy foal, and be able to ambulate in safe paddock conditions, often at a canter," wrote Grant in Current Techniques in Equine Surgery and Lameness.
There is, of course, a bright side, and that's the simple fact that prosthetics allow a horse to continue living a fairly normal life. A mare Redden worked on in 1992 has lived at pasture with other horses since five months after her surgery--and she runs the herd. Harper's mare--now 18 and on her 14th year with a prosthesis--has more limited physical abilities. But she's nonetheless been bred five times by natural cover, and she has raised five of her own foals, plus two orphans.
While not all cases have happy endings, a significant and growing number do. And it's certainly a step forward from what Redden calls the dark ages, when "once a horse loses vascular supply to the lower limb, he's killed. This is an avenue for owners wanting to give back to their horses and to give that horse an acceptable quality of life."
HOW DOES IT WORK? The Prosthetic Process
Amputation and prosthetic procedures vary from vet to vet. However, the general chain of events is as follows:
- Amputation occurs under general anesthesia; a fiberglass cast is put on and the temporary prosthetic is attached to it. Transfixation pins might or might not be used.
A frog graft, if performed, is applied two to three weeks after surgery.
- One or more cast changes occur as the stump heals. Pins, if used, are removed about four to five weeks after the initial surgery.
- When the stump is fully healed and the leg shape has stabilized, a mold is taken of the stump and is used to create the permanent prosthesis, which is attached approximately three months after amputation.--Sushil Dulai Wenholz
ADVANCEMENT IN PROSTHETICS: Five Keys to Pushing Forward
Stop snap decisions--Barrie Grant, DVM, MS, Dipl. ACVS, co-owner of San Luis Rey Equine Center in California, thinks more horses could be saved if vets encouraged owners to stabilize injured animals for a couple of days, giving the owner time to understand all the options and make an informed decision.
Add physical therapy--Donna Harper, DVM, a veterinarian in Roswell, N.M., who owns a prosthetic-wearing horse and has worked with Grant on prosthetics cases, would like to see research done on using physical therapy before surgery to preserve and build muscle mass above the proposed amputation site. When a horse loses use of a limb, she explains, the muscles related to that leg quickly atrophy and tire easily under exertion. So the horse doesn't have enough strength to properly use a weighty prosthesis, and instead winds up dragging it and hopping on his three good legs.
Increase interest--Grant and Ric Redden, DVM, founder of the International Equine Podiatry Center in Versailles, Ky., emphasize that more advancement is possible, but it will take greater professional and public interest--and a shift in mindset--to stimulate and accelerate progress.
Build funding--Lack of funding is another barrier. Veterinarians with full-time practices can't focus 100% on prosthetics without financial support--for instance, from grants and insurance policy changes. With increased funding and interest from veterinarians and horse owners, "We could make tremendous strides and really turn people's thinking around in five to 10 years, so that we would be able to save seven out of 10 cases," Harper estimates.
Expand the skill set--Although word is spreading, Redden notes that this is still a pioneering field with limited information and limited experienced personnel. To help remedy this, Grant and Harper would love to see the development of centers throughout the United States where experienced staff specialize in equine prosthetics and teach others about the procedures. "All we need," says Grant, "is an angel to fund it!"--Sushil Dulai Wenholz
About the Author
Sushil Dulai Wenholz is a free-lance writer based in Lakewood, Colo. Her work appears in a number of leading equine publications, and she has earned awards from the American Horse Publications and the Western Fairs Association.