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January 13, 2006

Industrial Engineer Designs Unique Prosthesis for Lame Family Pet

  — Pioneering research uses osseointegration for attaching prosthetic limb

Dr. Ola Harrysson holds the prototype of the prosthesis attached to a model of the cat’s leg. (Photo: Becky Kirkland)

George Bailey, a pet cat, was born without the lower half of his hind legs. Instead of running and jumping with his housemates, George Bailey pulled himself along on the carpet. But thanks to industrial engineers and veterinary surgeons at North Carolina State University, George Bailey has received a unique new leg and foot designed to allow him to walk — and even jump — around the house.

Pictured is the model of George Bailey’s leg and pelvis with the prosthesis attached. (Photo: Jennifer Weston)

Dr. Ola Harrysson, assistant professor of industrial engineering, and students from his biomodeling class designed a unique prosthetic leg and foot for the cat with the help of Dr. Denis Marcellin-Little, associate professor of orthopedics at the College of Veterinary Medicine at NC State.

Traditional prosthetic limbs are not a reasonable solution for cats since they are sensitive about having things attached to them. So Harrysson and Marcellin-Little decided to try a groundbreaking new approach creating an artificial limb that would be permanently attached to the bone in the cat’s leg. The research pioneers the use of osseointegration in developing usable prosthetic limbs for animals. Osseointegration creates a stronger, permanent prosthetic limb that is attached to the bone by inserting an anchor into the bone and encouraging the bone tissue to grow into the biocompatible metal.

“There were many design challenges from an engineering standpoint,” said Harrysson. “The bones of the cat’s leg are very small and can easily break. We had to test several designs on the models before finding the best fit.”

Harrrysson used rapid prototyping technology that can create a 3-dimensional model from CT scans to first build models of George Bailey’s deformed limbs. Using the models, he designed a prosthetic limb with a long titanium nail that was small enough to be inserted into the cat’s tiny tibia and secured with four tiny titanium screws. A cuff of porous tantalum attached at the base of the nail allows the bone tissue to adhere to and grow into the prosthetic, making it stronger and permanent. A titanium post protrudes from the skin covering the bone and cuff, and the flexible prosthetic leg and foot can be attached to the post. The final prosthetic was made by the Department of Industrial Engineering at NC State and BioMedtrix, a biomedical company with the capability of creating the porous tantalum cuff that is needed for the bone tissue to integrate with the prosthetic.

In a first-of-its-kind surgery on March 22, 2005, Marcellin-Little inserted the nail into George Bailey’s femur and pulled the skin over the tantalum cuff. Following surgery, a wine cork was used to cover the titanium post below the surgery site to prevent the cat from snagging it on carpet.

“Designing the foot presented another challenge,” said Harrysson. “We needed lightweight, strong and flexible material to fabricate the foot. In human prosthetics carbon fiber is used, but scaled down to the small cat foot, it proved too stiff.”

Harrysson and his students tested several designs for the foot and finally settled on one made of spring steel covered with rubber for traction. The final foot design closely replicated the weight bearing and spring action of a cat’s foot and leg.

Just weeks after his surgery, even before the artificial foot was attached, George Bailey was able to run and play.

Harrysson has worked with Dr. Marcellin-Little on many bone modeling projects that have benefitted pets with deformities. Recently, he has begun work on modeling soft tissue to aid surgeons and modeling sinuses to help Duke researchers develop nasal delivery pharmaceuticals. In addition he is working with Dr. Elizabeith Loboa, assistant professor of biomedical engineering at NC State, to find ways to repair structural defects, called voids, in the skulls of small children.

— weston —

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