Replacing one lost leg is challenging, but what about two, three or four?

Martin Kaufmann trained as a prosthetist and began his ‘human career’ working at clinics in the American Midwest. But when his cousin’s dog had a stroke and lost function in one leg, he was struck by the lack of options for an injury­ he was used to treating in humans.

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“[I] was surprised to find that the veterinarians were talking about full limb amputation,” says Kaufmann. “That led me to the big question: why don’t our four-legged friends have the same access to prosthetics?”

Human prostheses have been common­ for several centuries, but until very recently the only options for animals with missing or partial limbs were euthanasia or amputating the full limb. Kaufmann found that most vets had never considered prostheses as an option; it simply hadn’t been part of their training.

“It just simply wasn’t part of any educational component, as it is for our human doctors and human surgeons,” he says. “Nobody had released any scientific studies saying dogs could actually use a prosthetic.”

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That lack of data is a problem. There are few researchers studying animal prostheses and not enough published studies to be sure if, or when, animals will benefit from prosthetic limbs – or to say with confidence that the prosthesis won’t cause them harm.

One point of contention is whether a prosthesis would help or hinder a four-legged animal missing just one leg. A three-legged dog running around at the park might seem happy – but that doesn’t mean he’s not taxed, says Kaufmann. “It’s simply the cardiovascular endurance required to complete a very simple or trivial activity: it’s tremendous.” Not to mention the possibility of causing new injuries.

“If they have two incomplete limbs, they are particularly suited for prosthesis because quadrupeds don’t do well on two limbs,” says Denis Marcellin-Little, Professor of Orthopaedic Surgery in the College of Veterinary Medicine at North Carolina State University. “On three limbs, it becomes more debatable; some are more compromised than others.”

Even when a prosthesis is fitted, there can still be problems with getting the animal to use it. “Often the limiting factor in the success of a prosthesis in companion animals is [the animal] wondering what that thing is doing on them,” says Marcellin-Little.

Communication is where prosthetists can run into trouble, especially if the device isn’t perfectly comfortable or stable. “You can’t ask a three-year-old how he feels the prosthetic is fitting and functioning,” says Kaufmann, “[and] you can’t ask a canine how he feels about that one change you just made...Everything has to be clinical assessments and data driven.”

The enormous variety in the size and anatomy of different animals is another challenge: learning a whole new set of musculoskeletal concepts is taxing to say the least. “How are you going to give the patient the quality of life it deserves when you have to learn ‘Well, how does this stork actually work? What’s normal for a stork?’” asks Kaufmann. There are also important physiological differences to take into account. In 2007, for example, an elephant that stepped on a landmine as a calf was fitted with a prosthetic leg in Thailand. “Like most animals, elephants sweat through their extremities for heat regulation,” says Kaufmann. “So wearing a prosthetic can affect their heat retention. This caused the elephant to flap her ear a lot more to compensate.”

Kaufmann and his wife Amy run Orthopets, a company that’s made veterinary prostheses and orthotics for 12 years (prostheses replace missing body parts, while orthotics are braces that support or protect injured body parts). Large dogs are easy, he says – they are the size of small adolescent children – but most of Kaufmann’s canine patients are smaller than a two-month-old child. “You end up trying to deliver a prosthetic to a two-pound dog who runs around like a little crazy person.”

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Meanwhile, cases of new animal prostheses make the news again and again. In the past few years alone, there’s been Dudley, a duck with a 3D-printed leg; Beauty, an Alaskan bald eagle with a prosthetic beak; and Smaug, a Komodo dragon, fitted with a brace to stop him from walking on the wrong side of his foot. Marcellin-Little recently fitted an orthotic brace to a sea turtle’s injured flipper to stabilise the limb while it was healing.

Challenges abound: “How do you go about creating a solution for a dog who’s missing parts of all four legs and who is essentially walking blind to the ground?” asks Kaufmann. “[It’s] just incredibly complex.” However, meeting these challenges might reveal or refine techniques that could be useful for both animals and humans – such as implant prostheses, where a prosthesis is attached using a tiny rod inserted directly into the bone. “We’re able to do that in animals in more depth than we’re able – or allowed – to do in humans,” says Kaufmann. If this technique can be perfected, it could be a useful way of overcoming the suspension challenges of traditional prostheses.

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This article by Jocelyn Timperley originally appeared on Mosaic Science. It has been reprinted by permission. Read Mosaic Science’s series of stories on prosthetic limbs here.

Top image via the OrthoPets Facebook page.