Video: Three-legged dog back on all fours

NBC News and
updated 8/1/2008 8:44:13 PM ET 2008-08-02T00:44:13

For the first time, scientists have implanted a prosthesis that will allow them to directly fuse an artificial leg into a dog’s bone, a procedure that could foster a breakthrough in designing next-generation artificial limbs for humans.

In the four-hour operation Thursday at the North Carolina State University Veterinary School, Denis Marcellin-Little, an associate professor of veterinary orthopedics, fused a titanium implant onto what was left of the leg bone of Cassidy, a 5-year-old German shepherd mix who lost his right hind leg several years ago.

When Cassidy is discharged and goes home Friday to Long Island, N.Y., his leg won’t look much different, except for the visible tip of the implant. When Cassidy returns in the fall, the prosthetic leg should be ready to try.

Ola Harrysson, an N.C. State engineering professor who developed the hardware, said he and his team were still working on computer models for the design.

“Right now, we are designing a prosthetic leg for Cassidy that will have sensors in it to measure the force," Harrysson said. “That way, we can fine tune the strength.”

‘I was saving a life when I took him’
For Cassidy, the future holds the likelihood that he will be able to run normally again.

Steve Posovsky adopted the dog after he saw him on the pet segment of a morning television show. Cassidy was “unadoptable” because he had only three legs, Posovsky said, but he felt their relationship was meant to be.

The titanium implant was fitted over the remaining bone in Cassidy’s lower leg.  Doctors say it will take about three months for the bone to fuse with the implant.

“What his future was at that place was unknown,” he said. “I just knew deep down that I was saving a life when I took him.”

Posovsky began investigating what could be done for Cassidy almost immediately. In October 2005, he and his wife, Susan, took the dog to N.C. State’s vet school.

Marcellin-Little first tried two conventional prosthetics, but Cassidy wouldn’t wear them. He then suggested the new procedure, called osseointegration, which he had been working on Harryson and other engineers at the university’s Department of Industrial and Systems Engineering.

Marcellin-Little had previously tested it successfully on two cats, George Bailey and Mr. Fonz, but Cassidy’s surgery was the first time it had been attempted on a large animal.

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Conventional prosthetic limbs use sleeves that are placed over the stump of a limb and secured on the outside. In the procedure Thursday on Cassidy, a prosthesis was anchored into the bone, much as 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 so it can be stable for the long term.

“We let the bone rest and merge with the implant for the three-month period or so it takes for that implant to be firmly anchored,” Marcellin-Little said.

Promise for more normal human limbs
The result is a custom-designed prosthesis that behaves like a natural limb, a technique with significant promise for human prosthetics.

The Department of Veterans Affairs said that more than 1.3 million injured veterans need prosthetics every year and that the demand is rising as more service members come home from Iraq and Afghanistan missing limbs.

With new prosthetic technologies a priority of VA research, “the implications for this procedure are huge,” Marcellin-Little said.

“As we gain more experience with the surgical technique and the design of the limbs, we see the possible benefits for humans — implants that allow the prosthetic limbs to attach without chafing or irritation, and limbs with more natural ranges of motion,” he said. “We believe that this is the future of prosthetics.”

Harrysson said the hope was that it could be used on humans “on a regular basis. ... We see this process becoming even faster and more cost-effective in the future.”

Eventually, he said, a person could “be able to receive a CT scan from a hospital and probably, within days, turn this around.”

Julie Henry is medical correspondent for NBC affiliate WNCN of Raleigh, N.C. Alex Johnson is a reporter for

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