mitzi s new foot, $3,000. her owners don t care. loads of people spend thousands on boob jobs. reporter: operations like these on oscar and mitzi have never been tried in the u.s. next month. fitzpatrick will fly to chicago to take part in the first such procedure on american soil. people who say it is only a dog, i don t understand that. because you have never experienced unconditional love. you just haven t. because if you had you would never say that. reporter: he believes humans have a responsibility to look after animals. he insists he is not experimenting, but he is pushing medicine forward. every living creature is just flesh and bone. so what we do here may benefit another dog, may benefit another human. the most important thing is this dog today. reporter: this dog, barney, needs a new hip.
engineering. the perfect marriage of biology and mechanics. reporter: oscar s feet were slice off by a combine in a field. now he can run again. if the legacy helps animals, and then humans, there is no losers. reporter: mitzi was first to benefit. her foot was trampled and severed by a horse. there is a big piece of metal here inside the ankle bone. reporter: i am not a dog owner. i find this bizarre. you probably do. i love her. i want her to have four legs. reporter: her new leg behaves like a deer antler, skin and hair grows on to the revolutionary prosthesis.