The Prosthetic Problem With Animals

Although orthotic intervention for animals has come a long way and continues to evolve, the same cannot be said for prosthetic care, for several reasons. Bobbie Adams, RVT, CCRP, MSPO, LPO, veterinary O&P strategy and development coordinator, OrthoPets, Colorado, points out that a lot of the prosthetic componentry that exists on the human side does not exist yet for animals—like microprocessor or polycentric four-bar knees for dogs. “So for the majority of successful candidates for prosthetic intervention, we need a lever arm,” she says. “We need the level of amputation to be mid-radius/ulna, mid-tibia/fibula; the dog would be missing the paw and the carpus or tarsus (the wrist and the ankle), and there aren’t too many of those that exist in the world. An amputation at that level was likely planned by the vet because they talked with someone that knew something about prosthetics for animals. “The trickiest part of animal prosthetics is suspension—how do we keep these devices on?” The most common indication for amputation in dogs is osteosarcoma or severe trauma to the limb. And when those things occur, the vet’s first thought is to amputate at the level of the scapula, or the level of the hip, Adams explains. Currently, there are no joints available to replace the canine hip-knee or forelimb joints. But there is a prosthetic solution for a pet who is missing an entire limb. “There are companies out there that make a peg leg and attach it to a 3D-printed vest, which in theory levels the pelvis or the shoulders so you have a peg leg to stand on, biomechanically. But it still doesn’t bend and function like a regular leg, so the animal would have to compensate.” She points to recent research on the consequences to a quadruped following a whole-limb amputation. “We’re finding that they don’t do nearly as well as we thought they did. “In the quadrupeds, two front limbs take 60 percent of the body’s weight, and the two back legs take 40 percent. When a pet has a forearm amputation at the scapula, the remaining carpus (wrist) experiences substantial increase in weight bearing. “This is not how biology intended this animal to function. The situation creates a lot of problems with that remaining carpus, and we find that these dogs go into extreme hyperextension,” Adams says. “So when people approach me about a full-limb prosthesis for a pet, I explain what we can and cannot do, and then I redirect their attention to the carpus, which they need to be watching. Their veterinarian should evaluate it promptly and follow up with a discussion of the need for a carpal orthosis, to prevent hyperextension, control the joint, and so forth. That’s something that veterinarians don’t think about.” Jim Alaimo, CPO, co-owner, My Pet’s Brace, Pennsylvania, notes that what’s interesting about the field of animal O&P is that even after 13 years, they’re always learning new ways of doing things and discovering new materials. “The coolest thing I see currently is some of the 3D-printed devices that allow us to think out of the box and come up with a design that we couldn’t do through a lamination or pulling plastic, and it could be economically feasible. “Right now, we’re excited about the full-limb prosthetics that we’re able to do for some of the three-legged dogs that we hadn’t been able to fit before.” The reason one sees so many three-legged dogs, he explains, is that most veterinarians are taught in school that when a dog is injured in an automobile accident or other trauma, it’s easier to take off the limb at the shoulder or hip, disarticulating without cutting through muscle—and the dog will have no problem running on three legs. But the reality is that Alaimo’s busy making elbow braces and knee braces for joints overstressed and injured due to the added burden of weight bearing on their remaining limbs, which are working overtime to compensate for the missing limb. Sure, they’ll walk on three legs as long as possible, until they get fatigued or injured; and once that happens, the dog is down. If they’ve injured their Achilles tendon or their wrist, they’re down for a long time.” But My Pet’s Brace recently began partnering with 3D Pets, a New Jersey-based company that works with veterinarians around the country to develop never-before-possible prostheses for three-legged pets with no residual limb to which a prosthesis might be affixed. “We take a cast or scan of the dog’s body,” Alaimo says. “They do the manufacturing of the prosthetic device. If we can scan, we will. If not, we’ll take an actual cast. At this point we’re just doing front legs; rear legs are still pretty tough. “I’ve been doing this for 13 years—and we’ve seen so many dogs that had missing front legs or very short, above-elbow amputations. With humans we have suction or vacuum prosthetic sockets, but you can’t use that on a dog. It’s nearly impossible to get things to suspend on a dog or any animal because of their hair. You have to have a mechanical component that actually holds them on. “But now 3D Pets has designed this special harness that lets us attach Ottobock or modular components—they solved a problem that I’ve been trying to resolve over several years.” Ben Blecha, CPO, founder of Hero Braces, Nebraska, is also intrigued by new prosthetic possibilities. “I kind of abandoned prosthetics years ago, but now I’m looking at it again. Our model in this sparsely populated part of Nebraska is to work from a distance—and with prosthetics you have to have a much more intimate fit, so I’ve been a little more resistant to attempting it. But I do have some newly trained staff coming on board, so we’re looking at going back into prosthetics again. “There’s a company in Poland that’s trying to introduce some more 3D printing and scanning. But scanning dogs is really tough. Just one piece of fur in the wrong spot could cause a big false shape on the scan, and holding them in a natural position continues to be a challenge that a lot of people are still trying to overcome.”

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