A first-of-its-kind surgical procedure at North Carolina State University’s College of Veterinary Medicine will soon give a family cat, born without the lower half of its hind legs, the chance to walk with the help of functional prosthetic feet.
The project draws on the expertise of veterinarians, undergraduate students and researchers in NC State’s College of Engineering.
Efforts to help this feline, named George Bailey, to walk are the brainchild of Dr. Denis Marcellin-Little, associate professor of orthopedics. Marcellin-Little’s specialties are canine hip replacement and treatment of bone deformities in cats and dogs.
Marcellin-Little is attempting to pioneer the use of osseointegration in animals as a means of providing prosthetic limbs. Osseointegration is a new approach to helping amputees and is very different from using traditional artificial limbs. In osseointegration, the shaft of the artificial limb is inserted and anchored into the bone to provide a stable and permanent prosthesis. The use of osseointegration is rare even in humans — only about 60 people, mainly in Scandinavia, have undergone the procedure.
“I am in the middle of supervising a course with industrial engineering called bio-modeling. It’s a means of using engineering to help us solve complex orthopedic problems. Our idea is to find new forms of prosthetic devices,” Marcellin-Little said.
The cat in question was born without the lower half, or the tibia, of its back legs. “The buds that control the limb growth were damaged. This is a pretty unusual case,” Marcellin-Little said.
Typically, prosthetic limbs utilize sleeves that are placed over the stump of the limb and secured on the outside. “My thinking was that probably wouldn’t work for cats, since they are picky animals and likely wouldn’t tolerate that,” Marcellin-Little said. “The sleeve over the stump can also be painful and there is usually irritation or other skin problems.”
In osseointegration, the prosthesis is anchored into the bone — similar to the way an artificial tooth is anchored into the jaw — so it remains stable and locked in place. “Below that is a section for the bone to grow into for long-term stabilization. It’s really very similar to a total hip replacement,” Marcellin-Little said.
Marcellin-Little’s procedure will rely on the emerging technology of rapid prototyping to design and produce the prosthetic limbs. In rapid prototyping, a computer image of an object is transferred into two-dimensional cross-sections. Then, layer-by-layer, machines build a three-dimensional model.
“I’ve had my vet students involved in thinking about the design possibilities for the prosthesis and engineering students worked on the design as part of their bio-modeling course. It’s been a real brainstorm on something that’s never been done,” Marcellin-Little said.
The surgery will be the culmination of many months of effort. Initially, CT scans were taken of the cat and forwarded to two engineering students who had the primary responsibility of helping with design and function. “There were many unknowns. How do we shape the prosthesis? How are we going to design the osseointegration area and the area where it’s secured into the bone?” Marcellin-Little said.
After the CT scans, the prosthesis was designed on a computer and built in plastic, with rapid prototyping allowing Marcellin-Little to actually rehearse the most critical aspects of the surgery — the insertion and fixation of the prosthesis to the bone. “We’ve practiced the surgery in a model. We know how the new legs will work and how they will fit,” Marcellin-Little said.
The final prosthetic legs and feet are built with strong, lightweight biocompatible metal made by NC State’s Department of Industrial Engineering and an outside firm. “It’s pretty ambitious, but there is a lot of energy behind this project. There are a lot of great minds at work and lots of energy. There are no boundaries, since this has never been done before.
“The miniaturization of this could be the toughest part of this project. The multi-disciplinary nature of the project is a challenge, too. It involves basic medicine, orthopedics, prosthetics, biomodeling, designing an implant and then manufacturing. It’s radically different from what we’ve done before,” Marcellin-Little said.
And the ramifications could be significant.
“This could have a profound impact on how we view and treat amputees, because you could make a foot that replicates the motion of a natural foot. Think of all the people with diabetes who lose limbs. Someday maybe this will be an established way to do prosthetics,” Marcellin-Little said.
From North Carolina State