"We've still got our boy," said Mr Tane, a mahi whakairo (traditional wood-carver).
"That's the only outcome we wanted was to still have him with us. He's proved to us time and time again how strong he is."
Renata's ordeal with cancer began in January last year when, after he jumped off a rock at a beach, he complained of a sore leg. A doctor thought he had pulled a hamstring and although he had a limp when running, it was slight and little notice was taken of it.
The limp was mentioned to a doctor again. X-rays followed, a referral to Whangarei Hospital, then Starship children's hospital in Auckland and the cancer diagnosis was made: a tumour on the left thigh bone, just above the knee.
"Our whole world was shattered," said Mr Tane.
Renata had Ewing sarcoma, a rare disease that affects one to two children in every 100,000. It is a very aggressive cancer that is fatal if untreated.
Fortunately for Renata, the disease was detected before it had spread. He had chemotherapy, and the rotationplasty was done by orthopaedic surgeons Mike Hanlon and Andrew Graydon.
Video: How rotation plasty works
Mr Graydon said Renata was one of only six or seven youngsters in New Zealand to have had the operation, which was a "fantastic" procedure because the result was like a below-knee amputation, for which prosthetics worked better than for above-knee amputation.
The rotated foot retains full feeling and movement.
Although much of the mid-section of the leg, including the knee, is removed during the procedure, the full length of blood vessels and nerve are preserved without being cut; they are coiled up and fitted back inside the reconstructed leg. The larger bone from the lower leg is attached to the thigh bone with plates and screws.
The length of amputation is calculated to place the ankle alongside the knee of the other leg. The ankle then functions like a knee.
Mr Graydon said that once Renata got the hang of his prosthetic — it was fitted just over a fortnight ago — "he will be running with his friends on the beach. There will be no restrictions; he can do whatever he wants."
Renata's prospects were now bright: "He had a fantastic response to chemotherapy ... things are looking good for him," Mr Graydon said.
Mr Tane said he and Mrs Tane thought Renata would be devastated about the amputation, but they had explained about the cancer and the need for surgery, "and it just blew me away how good about it he was".
"For a while he missed his leg. He would hug what was left of it and there was some sadness because he couldn't get around as well as everyone else." But Renata, who loves swimming and play-fighting with his dad, is determined and independent.
"If he sets his mind to do something, he will do it."
• The Tane family has been helped by the Child Cancer Foundation. March is child cancer appeal month. To donate, visit childcancerappeal.org.nz.