Because Simon had coped well with his front leg in a cast, the couple were confident he would get by without left legs.
"When his leg was in a cast he would tuck it up and not even use it, or he would use it like a crutch, so we knew he would cope okay," McCarthy said.
It wasn't long before Simon was moving around the couple's Auckland home, flying up stairs and rolling around with his fur-siblings, Olive the cat and Barry the dog.
"He races around with them, chases skinks and runs after our chickens," McCarthy said.
"He bounced back in no time and was tackling everything from stairs to jumping on the couch and the beds."
The operations have cost the couple upwards of $22,000 - but they have no regrets and would do it all again for the cat they consider a family member.
"I stopped counting at $22,000," McCarthy said.
"It sure is a lot of money but putting Simon down wasn't an option, he's part of our family."
The first operation to try and save the leg was $7,000 - which the couple's pet insurance paid $3,500 toward.
Thousands of dollars went on a stay in intensive care, medication to fight infections and other treatments, check ups and dressing changes before the leg was eventually removed.