ACC is blaming wear and tear for patients' injuries and unfairly rejecting their claims, a study says.
The study, published in the New Zealand Medical Journal, said the ambiguous term "degeneration" was being "used and abused".
ACC often said injuries were caused by pre-existing degenerative conditions, it said. However, interpretation of the terms degeneration and degenerative could be "misleading and confusing".
The report cited the example of a 28-year-old nurse with 10 years' exposure to heavy lifting, who was told her back pain was due to age-related degeneration.
"More likely, lifting heavy patients and to a lesser extent gardening and playing netball have combined to produce the lumbar disc protrusion," it said. "The decision not to grant compensation in this case was neither logical nor just."
The study was written by health professionals Richard Wigley, Christopher Walls, David Brougham and Peter Dixon.
They recommend the word "degeneration" should be replaced by clinical terms with more meaning. This would prevent false assumptions, leading to flawed legal decisions that "hindered patients' rehabilitation".
Wellington man Brandon Dixon had an ACC decision not to fund surgery on a prolapsed spinal disc overturned last year.
His claim was initially declined because medical scans showed there was also degenerative damage near the injury.
Last year Judge Martin Beattie ticked off ACC for seizing on age-related degeneration of claimants' bodies as a reason for unjustifiably rejecting their claims for surgery after an injury. ACC said it recently tightened decision-making for elective surgery.
A review made public this month found that, since early 2008, ACC has been scrutinising elective surgery requests, such as for shoulders and knees, more closely.
The proportion of surgery applications turned down increased from 11 per cent in 2007-08 to 22 per cent in 2009-10, the review said.
The number of decisions on elective surgery overturned on review also rose over that time to an average of 44 per cent compared with 25 per cent for other claims.
Arthritis puts couple 'between rock and hard place'
Russell and Julie Smith face tough times with their claims to ACC because of arthritis found near their injuries.
"OK, there is an ageing process, but I feel I am being penalised because of it. It's left us between a rock and a hard place," Mr Smith said after his claim for an injured shoulder was rejected.
Mrs Smith, 54, a kindergarten teacher, hurt her hip after she fell over some children at work. She suffered a chipped bone in her hip, and now needs the joint replaced, but has heard her claim may be rejected after evidence of arthritis was found there.
She faces a $20,000 bill to go private, or a wait of up to 15 months in the public health system.
She is in constant pain and finds moving around difficult.
Mr Smith, 64, a vehicle inspector, hurt his shoulder when he slipped while pushing a car. His claim was also rejected when evidence of arthritis was found.
Although he had surgery on the shoulder in 1999, there were no problems until he fell, he said. He is challenging the ruling through ACC's review process.
While the Palmerston North couple are both "battling on" at work, they are facing months at home, and huge medical bills if their claims are rejected.
- The Dominion Post
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