Prosthetic leg makes dog Cassidy a medical pioneer living in Delray Beach

By LONA O'CONNOR

Palm Beach Post Staff Writer

Friday, March 06, 2009

Cassidy the dog was on his last legs - three of them, to be exact. He was featured on a morning television show, scheduled to be euthanized in 48 hours, mangy and bony from living on the street.

"They were looking for morons that want to adopt a dog," said Steve Posovsky, a Queens, N.Y., dentist with a self-deprecating sense of humor. "So I drove to Manhattan and took him home."

Since Cassidy met Posovsky, 61, his fortunes have been on the rise.

Posovsky and his wife Susan, who spend most of the year on the ocean in Delray Beach, made it their quest to find an artificial leg for Cassidy, who lost his right rear leg before he was adopted.

Cassidy got his leg and has become a pioneer in animal surgical annals, with a prosthetic that is actually part of his body. The scientists who worked on him are hoping the technique might someday be used on humans.

Online research and talking to veterinarians led Posovsky to Dr. Denis Marcellin-Little, associate professor of orthopedic surgery at the North Carolina State University College of Veterinary Medicine in Durham, N.C. The veterinarian had already implanted prosthetics in living bone tissue on two cats. The procedure is called osseointegration, and in humans the most common example is tooth implants.

The base of the leg was permanently installed in Cassidy's thighbone, where bone and titanium implant grew together as one. The lower part of the leg screws into the titanium base.

Dr. Ola Harrysson, associate professor of industrial and systems engineering, worked on the mechanical aspects of building a titanium implant with a "circuit breaker," a system of strong magnets that separate if the remaining portion of the dog's natural leg is in danger of breaking.

Cassidy, who had thrown off external prosthetics, did not take well to the implant. So the Posovskys tried the prosthetic on him for just a few minutes a day. If Cassidy accepted this artificial leg, the NCSU team would provide him with a permanent version they were working on.

"Around Thanksgiving, he just woke up one morning and started using it," said Steve Posovsky.

On Monday, Cassidy and the Posovskys head back to North Carolina for a final version of the leg, resembling the curved carbon-fiber "C-legs" used by amputee runners. It will add a more natural spring to Cassidy's step than the training leg, which operates like a stiff spring-loaded telescopic tube.

The surgery and cost the Posovskys about $6,500 plus travel and other costs, with the university absorbing as research costs the many hours of trial and error.

The team at NC State hopes that their work will contribute to worldwide efforts to improve prosthetics, but for now, Marcellin-Little describes it as "only one piece of the puzzle."

Harrysson is working on projects benefitting humans, including a spinal cage for use in surgery on damaged vertebral discs, as well as polymer implants that gradually dissolve as new bone grows around them.

Ultimately, if veterinary techniques can be adapted, human amputees can benefit from more comfortable, effective prosthetics. The external prosthetics commonly in use now must be replaced regularly, and refitting is slow and painstaking.

Cassidy's surgery got attention in the Research Triangle area of North Carolina and in medical and engineering journals. Marcellin-Little is now hearing from dog owners and humans eager to try the technique. He is also exchanging notes with surgeons considering the technique for replacing human limbs. A few human subjects have had a procedure like Cassidy's, done by doctors in Sweden and Great Britain.

The professors are happy with Cassidy's progress.

"He used to have weakness and fatigue, and now he can walk for hours. He's a happy dog, and that's about as good as it gets," said Marcellin-Little.

"You wanna go to the beach with Daddy?" Posovsky asks the dog, who barks his agreement.