Another factor was the rising demands of patients to be more active and have a better quality of life in old age.
While the the number of publicly funded spinal fusions a year has increased rapidly to 1093 in 2010/2011, the proportion funded by the Accident Compensation Corporation has declined slightly since 2008.
The number of ACC-funded fusions dropped from 729 in 2008/2009 to 651 in 2010/2011 - and rose to 660 in the 2012/2013 year.
The cost to ACC in that year, was $8.72 million.
Spinal fusion involves fixing two or more vertebrae together with rods and screws or bone grafts. It has traditionally been done to treat spinal deformities, trauma and other conditions such as tuberculosis or tumours.
"What's crept up over the years is spinal fusion for back pain ... in parallel with spinal fusion in association with decompression," said the president of the Spine Society, Dr Robertson.
Decompression surgery can involve removing part of the fibrous disc between vertebrae and trimming out arthritic bone spurs - to reduce pressure that has built up on a nerve.
Dr Robertson said that in decompression, "there can be a point where you take so much bone away that you need to restabilise the spine [with fusion]".
Fusion for back pain was done mainly in people aged 25 to 60. Fusion in association with decompression was mainly in those aged 50 to 80.
"There is increasingly clear evidence fusion in association with decompression where necessary in the older age group is easily equivalent, in terms of quality of life improvement, to hip and knee replacement.
"The area of controversy is the fusion for back pain group in the working-age population.
"The research literature is hugely confusing about that. You can find a perspective to support any argument," said Dr Robertson.
"The difficulty with fusion for back pain is determining why the patient has back pain ...
"The odds of the surgery being successful are better when it's more clear-cut what the likely cause of [the pain] is.
"When a patient asks, 'Will you do a fusion on me?' it's usually because they are in a great degree of pain and disability.
"They are there because it's a tremendous disruption to their life and they've failed everything else - physio, chiropractor, osteopath and acupuncture."
'All ACC ever want to hear is degeneration'
Shanil Vellaidan is only 33, but accident compensation officials rejected his surgery funding claim on grounds of degeneration in his spine.
The West Auckland vehicle mechanic, homeowner and father of two was astounded that ACC intended to force him off his earnings-related compensation after one of two spinal specialists he consulted made mention of degeneration.
But after the Herald made inquiries with the Accident Compensation Corporation on his behalf, ACC said it would have another look at his case and has rescinded its plan to stop his compensation payments.
"Given the complexities of this case and contrasting specialist opinions, we're now taking the time to review the medical information," said ACC spokeswoman Stephanie Melville. "While this is under way, we will continue to pay weekly compensation for Mr Vellaidan.
"ACC will seek additional specialist medical information as regards any injury-related need for surgery. We'll contact Mr Vellaidan once the review is completed."
The case comes after claimants quoted in the Herald criticised ACC's surplus of $4.9 billion for 2012/13. One said it was a ridiculous financial result when many people's claims - including her own - were being rejected on grounds of degeneration.
Mr Vellaidan's injury occurred at work in October. He was lifting a converter - a 15kg to 20kg part of an automatic transmission - from a bench to a lathe, when he felt sharp pain down one leg. The pain was so intense he dropped the converter.
He is taking pain medicines, but they give him only moderate relief.
He has had two previous episodes of back pain. The first was in 2011 when he picked up his eldest son, now 4, after the boy fell. Mr Vellaidan was treated with cortisone injections.
He said that after the latest injury, orthopaedic surgeon Michael Barnes recommended an operation on the lower spine. The operation would involve fusing two vertebrae together with pins and rods.
But before seeing Mr Barnes, he consulted orthopaedic surgeon Clayton Chang. He indicated surgery was a possibility, but in his report also wrote of degeneration.
"ACC turned me down because I have this degeneration problem. They have gone for the report from the first specialist who said it's worn a bit and could be degeneration and the second specialist said it's not and it needs to be operated on.
"[Mr Barnes] said that at my age, degeneration is not right. He said it's a prolapsed disc, not degeneration. All ACC ever want to hear is degeneration."
