A 16-year-old rugby league player hobbled on a torn knee for two months and was forced to pop it out when it jammed, while ACC assessed the surgery he needed.
His mother says ACC wavered over whether the injury was new, even though he had suffered it during training. It eventually approved the funding after Labour MP Andrew Little intervened.
The case comes 10 months after ACC said it would improve its service following a Herald campaign that revealed an excessively hardline policy for elective surgeries.
An internal review issued recommendations to address the concerns.
ACC last night said it had taken the recommendations seriously, though chairman John Judge attacked the original criticism by saying that many complaints had been based on "inane claims".
Tracy Stowers, whose son did not want to be named, said it had been terrible to see her athletic boy in pain.
"I was really, really upset - it was about my child. You would be too if your son needed surgery and they kept mucking you around."
The 16-year-old was hurt in December while training, and his doctor immediately assessed that he needed surgery for a torn cartilage.
But he had previously suffered a torn meniscus a couple years back, and the surgeon was not able to get a clear picture of the injury without opening up the knee.
An application for ACC funding was lodged just before Christmas and surgery booked for the second week of January. But it was pushed out week after week while ACC delayed its decision.
Ms Stowers said that first the case manager needed a note from a physiotherapist, then the opinion of an outside assessor - and each time took longer than promised for the extra information.
"When an answer came, she said they can't make up their minds. They're going to send it to another surgeon for another opinion.
"It was like they wanted to keep sending it to people until someone said 'no'.
"I felt really helpless," Ms Stowers said. Mr Little said it was clear the surgery should have been funded.
"I had a look at the material, including two medical opinions ... there should have been no hesitation - it was inexplicable that there was."
He wrote a letter to ACC and soon the surgery was approved.
"There's a culture that comes right from the top about clamping down on the approval of claims and money being spent on recovery and care," Mr Little said.
"It's gone so far that now you've got frontline decision-makers reluctant to make decisions.
"It's pretty clear. ACC has been around for 40 years - if you have an accident and you get injured, you're entitled to cover. It's not that difficult."
An ACC spokeswoman said the corporation wanted the best outcomes for clients and could sympathise with a family who had to wait while a family member was in pain.
"This would appear to be more about a delay in the decision-making process as opposed to what could be deemed as a wrong decision or right decision," she said.
Chief executive Ralph Stewart said last night the recommendations from last May had been taken seriously - and the corporation would provide a full response about how it had improved its services today.
"ACC is active and constantly trying to improve how information is managed between the medical profession, ACC and in respect individual claimants' privacy rights," Mr Stewart said.
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