Naki'o, a mixed-breed puppy, received four prosthetic limbs in Denver, Colo. Naki'o was found with all four legs and his tail frozen in puddles of water-turned-ice. What frostbite didn't do, a surgeon did, amputating all four legs and giving him four prosthetics.

LOS ANGELES — A 9-month-old boxer pup named Duncan barreled down a beach in Oregon, running full tilt on soft sand into YouTube history and showing more than 4 million viewers that he can revel in a good romp despite lacking back legs.

“It's a heartwarming, wonderful thing to see,” said Dr. Bonnie Beaver, a professor at Texas A&M University's College of Veterinary Medicine and executive director of the American College of Veterinary Behaviorists. “These animals generally look to us as if they are very happy. We don't know that they are, but they are excited and jumping around and doing things that are wonderful to watch.”

But dogs aren't made to stand, and they are putting unwanted pressure on their joints and probably shortening their lives, Beaver said. Duncan's owners say they are “keeping a vigilant eye” on the animal who balked at a doggie wheelchair and can't use prosthetics.

“Vertical postures are not normal for four-legged creatures,” Beaver said. “The use of a prosthetic can give that animal a more normal life.”

More veterinarians are using wheelchairs, orthotics and prosthetics to improve the lives of dogs that have lost limbs to deformity, infection or accident, experts say. The move is driven by persistent pet owners who embrace their animals as family and aren't deterred by the cost and commitment of outfitting disabled dogs with the devices. At the same time, there have been great strides in technology to keep up with U.S. soldiers returning wounded from war, and veterinarians have adapted the materials and know-how for the rising demand from clients.

“There are so many things we can do to solve mechanical problems. ... If you have broken parts, we can replace them,” said Martin Kaufmann, co-owner of Veterinary Orthotics and Prosthetics in Denver, also known as OrthoPets, which helps about 2,000 animals a year.

Most devices range from $150 to $2,000 but can cost more, Kaufmann said.

Besides commercial manufacturers, there are likely thousands of backyard builders who have created carts, slings or other devices to help their pets get around.

The number of pets using artificial limbs will never be huge, Beaver said. It takes a dedicated person willing to take the prosthetic on and off, clean it and teach the animal to use it.

There have been successes even in challenging cases, Kaufmann said. Orthopets helped mixed-breed puppy Naki'o after his four legs and tail were frozen in ice. What frostbite didn't do, a surgeon did, amputating all four legs. Then, Kaufmann outfitted him with four prosthetics.

“To see Naki'o at the beginning, he was protective and guarded,” he said. “Six months after all this was done, he was just a fun-loving guy who likes to socialize.”