The Wild World of Animal Prostheses

Motala had her foot blown off by a land mine; Fuji lost most of her tail to a mysterious disease; Stumpy crippled her leg in an unknown injury in the wild. Only a few years ago, a wounded elephant, dolphin and kangaroo like these would not have had much hope. Under the rough rules of the wild, they would have quickly died of predation, infection or starvation. Compassionate humans who intervened might have been able to make the animals more comfortable but never could have made them whole.

Now that's changing. With the help of some fancy new prosthetics, a cutting-edge subset of veterinary surgeons is learning how to transform lifeless pieces of metal and plastic into working feet, legs, tails, and even (nonworking) dog testicles. The animals regain the ability to live like healthy creatures, something the surgeons find rewarding enough. More important, what the doctors learn as they put the critters back together could help the medical community work similar magic on humans. That's progress that couldn't come at a better time. There are currently about 1.9 million amputees living in the U.S., a figure expected to jump to 2.7 million by 2020--mainly because of returning Iraq war veterans and patients who lose limbs to diabetes-related complications. "We can't sit back and let helpless animals fend for themselves," says Dr. Erick Egger, associate professor of small-animal orthopedic surgery at Colorado State University. "We need to help them, and more important, we need to help people."

Human and animal prostheses are in dire need of a makeover. Typically, the stump of a damaged limb is simply inserted into a socket at the top of a prosthesis and held fast by a plastic sleeve or belt, or suction. The prostheses themselves might have gotten lighter and more flexible over the years, but the stumps' socket attachments have remained largely unchanged--and that's not good. It can be notoriously unstable and is prone to causing breakdown of soft tissues, as constant rubbing leads to pain and infection.

Animals have had it even worse. If prostheses existed at all, they have been comparatively crude things. Surgeons have had some success attaching artificial beaks to birds that veterinarians suspect were mutilated by fishermen who didn't want the animals competing for their catch. Dogs and cats with disabled hind legs are often strapped into little carts that let them get around using just their forelimbs. But those low-tech fixes had been more or less as far as it went.

When Motala the elephant stepped on a land mine eight years ago in Thailand, her prospects were bleak. Veterinarians were forced to amputate what was left of her mangled foot and part of her leg. The operation saved her life but left her hobbling around on only three legs for the better part of six years. Finally, in 2005 surgeons at the Friends of the Asian Elephant Hospital in Lampang, Thailand, designed a 22-lb. (10 kg) shoelike prosthetic foot that is little more than a canvas sack filled with sawdust and held in place by a giant sling. It's not much, but as proof of the principle that such an appliance could work, it counted as a breakthrough.

"I had my doubts," says caretaker Soraida Salwala, founder of the hospital. "I had heard of prosthetics for birds and dogs, but nothing had ever been made for an elephant." So well has Motala adjusted to her new foot, however, that doctors are already designing a lighter, sturdier replacement for her made of fiberglass and silicone.

Motala may be better off than she was, but even an upgraded foot won't help her walk like a normal elephant. So cases like hers have inspired surgeons to begin experimenting with some radical new approaches that could potentially transform the field of prosthetics. One method is known as ingrowth, or osseointegration, a technique that skips the sleeves and cuffs altogether and attaches the prosthesis directly to the bone. "It is one of the hottest ideas in the field," says Dr. Denis Marcellin-Little, associate professor of orthopedics at North Carolina State University, who tried the surgery (unsuccessfully) on a cat two years ago. "And it has the potential to greatly improve the life of humans, especially soldiers."

The ingrowth method works by inserting a porous metal implant straight into the end of the remaining bone. Over a few months, the bone grows around the implant, providing a strong anchor onto which a prosthesis can be attached. Scientists are even finding that the softer muscle and skin tissue that also grow into the pores help prevent infection by producing a bacteria-resistant seal. That is exactly what Noel Fitzpatrick, a veterinary surgeon from Farnham, England, found when he successfully performed the procedure on a pawless pup named Storm a little more than a month ago.

While osseointegration has worked for at least half a dozen animals and has been attempted in at least 60 humans, mainly in Scandinavia, every animal presents surgeons with a different biomechanical challenge. Attaching a leg to a nimble, bouncing animal like a kangaroo is different from creating a limb for a plodding one like an elephant. When Stumpy the kangaroo lost her hind leg, surgeons designed a prosthetic foot--held in place by a traditional stump and socket--that is made of carbon fiber, which has the ability to spring back to its original shape after it is bent. This same technique is often used to make prostheses for human runners, like the ones designed for the famous double-amputee sprinter Oscar Pistorius. "Carbon fibers have a shape that will always come back," says Rick Nitsch, a prosthetist from American Orthopedics in Columbus, Ohio, who designed Stumpy's bouncy leg four years ago.

What about an animal that isn't supposed to have any legs at all and yet still needs to get around? Fuji, the dolphin that lost 75% of her tail, had just enough left that researchers at the Okinawa Churaumi Aquarium in Japan could affix a rubber tail, designed by sculptor Kazuhiko Yakushiji, onto her mangled tailfin with reinforced plastic and metal screws. Winter, a dolphin that lives at the Clearwater Marine Aquarium in Florida and is completely tailless as a result of an injury from a crab trap, presents a much bigger challenge. Hanger Orthopedic Group in Bethesda, Md., thinks it can help, using a sticky, gel-like material to create suction between the damaged limb and the prosthesis that will help hold it in place. The detachable tail may leave Winter too vulnerable ever to return to the wild but will allow her to swim again. What's more, the gel lubricates just enough that it helps protect against irritation. That led Hanger to recommend it to a legless soldier who had been suffering from recurrent infections. Since then, his skin has cleared up, and now he can tolerate his prostheses again.