How prosthetics enable specially-abled pets
Prosthetics for people have been around for millennia. A 3,000-year-old mummy was recently discovered sporting a prosthetic big toe. Believed to be the oldest prosthetic in the world, the workmanship was amazing; the wooden toe had been carefully crafted to fit the woman’s foot, and could even flex.
Animal prosthetics are a relatively new phenomenon, but their technology is improving at a rapid pace.
So, when did prosthetics become a viable alternative?
A brief history of exoprostheses for dogs and cats
“Exoprostheses have been a viable option for more than 40 years,” Denis J. Marcellin-Little, DEDV, DACVS, told NEWStat. Marcellin-Little, professor of orthopedic surgery at the UC Davis College of Veterinary Medicine, was a pioneer in veterinary prosthetics and lead author of the 2015 paper “Orthoses and Exoprostheses for Companion Animals.”
Exoprostheses are devices that are secured to incomplete limbs to enable locomotion. By comparison, orthoses are devices externally applied to support or protect an injured body part. Both can have a profound beneficial impact on the mobility and the quality of life of companion animals. And both require precise design and fabrication. A prosthetic limb can give amputee dogs the same freedom and mobility that they experienced when they had all four limbs.
“I started working with exoprostheses in 1990, and devices were already being used,” Marcellin-Little added.
Not every amputee dog needs a prosthesis—many adjust very quickly to life as a tripod. But as well as they might seem to get around, walking on three legs requires that a dog shift their weight and balance, meaning that they have to support their body differently than a four-legged dog, which can place stress on the remaining healthy legs over time. That puts them at a greater risk for developing chronic pain and injuries down the line.
The Wizard of Paws
Derrick Campana, MSPO, isn’t a veterinarian, but he has a background in kinesiology and biomechanics and started out developing prosthetics for humans. He switched to animals in 2005 and founded Animal OrthoCare in Virginia the same year.
Since then Campana has become something like the public face of veterinary prosthetics through his television show The Wizard of Paws.
During that time, he’s fitted leg braces for camels, cranes, and a 12,000-pound elephant, but mostly he makes devices for dogs.
Campana told NEWStat that there can be complications for dogs following an amputation, including arthritis, joint degeneration, strain, reduced mobility, and phantom pain. But if successful, a prosthetic can prevent many of those long-term effects, and add years to a dog’s life. “I hear all the time that dogs can walk fine on three legs, but I want them to walk great on four.”
Not everyone agrees with that sentiment. In fact, said Marcellin-Little, there’s a wide range of attitude among people about how to manage physical disability in pets, and there are those who “would never consider recommending or using an exoprosthesis.” He said that for the devices to be effective, both patients and owners must be trained in how to use them.
Which patients do best with prosthetic devices
Just because an animal might benefit from a prosthetic device doesn’t always mean they receive one. First of all, are they a good candidate?
Marcellin-Little says that depends on a number of factors, including the age and size of the animal (very small and very large dogs pose greater challenges), the amount and health of the residual limb, soft tissue coverage, and skin mobility relative to underlying tissue. Other issues include possible orthopedic problems in the limb, how the limb is innervated, whether the partial limb is affecting the range of motion in adjacent joints, and gait issues.
The patient’s personality also plays a role. Is the pet friendly and easy to work with? How has it adapted to the loss of a limb? How active is the pet? Even the client affects the decision. Does the client own other animals? Does the owner have the time and is he or she committed to helping the pet learn how to use the prosthetic device? Most importantly, does the client have the patience to follow through, because optimizing fit and retraining can be very time-consuming.
Because every dog’s amputation is unique, their artificial limb needs to be custom made to fit them perfectly, which is why there are many different types of prosthetics limbs for dogs—for front legs, back legs, and even prosthetic paws.
“If a pet is missing part of a limb, evening out a pet’s body is essential for their health and wellbeing just like in humans,” said Campana. “A straight body/spine can lead to a happy healthy life/body and prevent further breakdown.”
Campana said the site of the amputation is important. “Generally speaking, the longer the residual limb, the better the candidate.” Size of the dog and date of amputation also play a part. “Larger dogs generally accept devices more readily and also animals with more recent amputations.”
Whether a prosthesis works depends largely on which limb has been affected and how much of the limb is intact. If a patient still has an elbow or a stifle (knee), for instance, there's a much better chance they’ll accept the device.
Another consideration is the length of time that has passed since the animal was affected by an injury or deformity, so the sooner the device is fitted, the better. Otherwise, the pet won’t accept it as easily, especially if they’ve been getting along fine on three legs.
Some of the challenges in getting a pet to adapt to a prosthesis include choosing the proper design, said Marcellin-Little. Others are optimizing long-term safety of the residual limb; achieving axial, bending, and torsional stability of the device on the limb; training the dog to use the device; and training the owner to don and doff the device and maintain it.
3-D printing prosthetics for companion animals
Marcellin-Little Denis started experimenting with 3D-printing prosthetics in 2002. “It makes sense to build components of exoprostheses based on 3-D renderings of partial limbs,” he said. “These renderings can be acquired using a laser scanner or a CT scan.”
Three-D printing, also known as additive manufacturing, involves making three-dimensional objects from a digital file with material such as plastics, resins, and metals. Three-D printing machines can cost anywhere from a few hundred dollars to many thousands of dollars, depending on their capabilities, but this technology has the potential to make manufacturing prosthetics not only more efficient but easier to customize—if a 3-D-printed prothesis doesn't quite fit, you can always adjust the digital file and print another one that fits better.
Unlike thermoforming, which uses heated and molded plastic to make a prosthesis, 3-D printing allows prosthetists to make the devices flexible in specific areas and rigid in others, breathable in all areas, and waterproof, which makes for a more comfortable—and more accurate—fit.
Marcellin-Little thinks that digital engineering in general—scanning, additive manufacturing—offers new options for the fabrication of exoprostheses, but says those approaches vary and depend on funds available and the willingness and ability of prosthetists to innovate.
“For example, Hanger prosthetics introduced [a handheld 3-D scanner] to some of their practices approximately 20 years ago but the transition from conventional fabrication—casting and fabricating the exoprosthesis based on a plaster cast—to digital fabrication is still in progress.” It’s why conventional casting techniques are still widely used to manufacture prosthetics.
“Three-D printing definitely plays a part,” Campana agreed. But he added that, contrary to popular belief, 3-D scanning isn’t necessarily a magic bullet: “The costs can be higher, and fabrication can take longer” than conventional casting techniques. However, he adds, “3-D printing is a great alternative for big builds since it can lower costs for these types [of devices] and can be easily reproduced.”
Companion animal prosthetics can offer a new life—to some
If all goes well, a prosthetic can be life changing. If the animal accepts it.
“Animals are incredibly adaptable, and resilient, but unable to rationalize the concept of an artificial appendage,” Campana said. “Because of that—and the fact they can’t communicate in words how they feel—it can be difficult to know whether a prosthetic is improving a pet’s life or causing stress and suffering. If they’re in pain, a prosthetic is useful. If they aren’t in pain, it can be more of a burden.”
He said it depends on the pet.
“Some accept them immediately and some never do,” he added. “You can’t tell an animal how to use something, and the longer I do this the more I realize that animals just have a mind of their own.”
Tony McReynolds is a temporarily petless freelance writer who lives near a dog park in Lafayette, Colorado. He dreams of one day owning a Newfie who isn't afraid of water (which the last one was, and seriously, how is that even possible?).
Photo credit: © PhonlamaiPhoto E+ via Getty Images Plus
Disclaimer: The views expressed, and topics discussed, in any NEWStat column or article are intended to inform, educate, or entertain, and do not represent an official position by the American Animal Hospital Association (AAHA) or its Board of Directors.