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‘HOP-ALONG’ CASSIDY GETS LEG UP IN LIFE

It gives one paws — or, at least, paw.

Bronx pooch Cassidy had just three legs to stand on until he got a fourth, thanks to a cutting-edge technique that made him a walking miracle.

The German-shepherd mix — well, OK, mutt — has become one of the few animals in the world to receive a permanent prosthetic limb, and is a trailblazer whose surgical experience could help humans.

The dog, who lost his right rear leg below the knee joint, had an “osseointegration” procedure in which a titanium implant was attached to the tibia, a leg bone. A removable, C-shaped foot made of titanium, carbon fiber and rubber screws onto the prosthesis.

“The implant is permanent and goes into the bone like a dental implant in humans, and then the bone and the implant fuse,” said Steve Posovsky, 61, a retired dentist from Long Island who with his wife, Susan, adopted Cassidy in August 2005, when the dog faced euthanasia.

Posovsky was watching a morning news program that showed “this dog that had been found in The Bronx with his leg cut off wandering the streets who was about 2½ years old.

“When I saw him on TV, I had to get him,” said Posovsky, who lives most of the year in Florida.

“He was 30 pounds underweight. He limped along. He had almost no hair,” recalled Posovsky, who said that before his surgery, Cassidy “would walk for 10 minutes and have to plop down and need a rest.”

“Now, he can walk for hours.”

After taking in Cassidy, he and his wife contacted Dr. Denis Marcellin-Little, a surgeon with the North Carolina State University College of Veterinary Medicine in Raleigh and had a removable prosthesis made.

Cassidy “kicked off” the leg, so they decided to go with a permanent one.

Last August, the permanent prosthesis was implanted, and last month, the final version of the foot was perfected.

“What is being assessed and being designed for Cassidy may improve our knowledge and may ultimately help in what is being done for people,” he said.

Meanwhile, Cassidy “is very happy,” Posovsky said. “He walks on the beach with me every day with his new leg. When he’s running I take his leg off. I’m a nervous father.”

rita.delfiner@nypost.com