ACC was the envy of the world, Mr Matheson said, and he had received many positive comments about the scheme overseas.
Mr Matheson, a past president of the New Zealand Orthopaedic Association who works in both the public and private sectors, said he understood the savings drive as costs had blown out.
"There's an advantage to being on ACC; there has been a trend to put some injuries as ACC when they should not have been."
However, now ACC was not looking at every case on its merits, Mr Matheson said.
More cases were going to review or appeal, which would result in bigger legal bills for ACC, and defeat the purpose of the cost-saving drive.
He had noticed big changes in the way knee and shoulder cases were considered.
Mr Matheson had encouraged some patients to seek a review or appeal.
"I only get involved when I feel the patient has been done an injustice."
Degeneration was cited too often for rejecting a claim when there had been a demonstrable accident which had caused the patient's symptoms.
"Yes, there might be degeneration, but if the patient had no symptoms [before], we contend it's a significant factor."
Recently, a woman aged about 50 with tennis elbow was turned down.
Mr Matheson considered her eligible for ACC.
She sought a review, winning her case.
"What annoyed me is that they would not accept my advice."
Mr Matheson has a particular interest in tennis elbow, having published research in international medical journals.
Specialists were already "gate-keepers", frequently advising patients their injury did not fall under the scheme.
Of concern was ACC's increased use of radiologists' reports rather than specialists'.
"I look at my own MRIs as I sometimes put a different interpretation on them."
Specialists took a patient's whole history and physical examination into account, he said.
Delays hurt patients, as reasonably prompt surgery was a factor in rehabilitation.
The changes increased pressures on the public sector.
However, many patients were not high in the public sector's priorities, and "fell between" the two systems.
Letting the private insurance industry into the sector could make things worse, and surgeons were actively "lobbying" against the prospect.
Private insurers placed less emphasis on rehabilitation.
Dunedin ACC lawyer Peter Sara had seen a ten- to twelve-fold increase in orthopaedic cases in the past year or so.
Orthopaedics had not been targeted in such a way before, Mr Sara said.
Labelling the corporation "reckless", Mr Sara said ACC was citing degeneration in an overwhelming number of cases, using "spin" to justify unacceptable decisions.
In one "ridiculous" example, a fit, healthy 38-year-old mother active in netball playing and coaching was turned down for cover for a shoulder injury after an accident due to age-related degeneration.
Employing a "conjuring trick", ACC was citing age-related degeneration in an overwhelming number of cases.
While ACC did not cover pre-existing conditions, the "egg-shell skull principle" was relevant, meaning pre-existing vulnerabilities did not exclude a person from cover.
Responding by email, ACC clinical services director Dr Kevin Morris said ACC was declining more surgery claims and putting them under greater scrutiny, as there had been a huge rise in claims.
ACC decisions were generally upheld under review, he said.
Declining claims due to a pre-existing condition or age-related degeneration was legitimate, and within ACC legislation.
"This is not new or something that ACC staff have suddenly made up.
"There needs to be an injury that was the result of the accident, not a pre-existing condition.
That's the law."
Responding to concern about radiologist's reports used over orthopaedic surgeon's, Dr Morris said while ACC "recognises the role" of orthopaedic surgeons, it was "quite right" to use a range of medical practitioners to make decisions.
Those not eligible for ACC could seek assistance from the public sector.
"I understand the temptation for clients and surgeons to push for ACC cover, since the benefits are attractive, especially if time off work is required, but ACC is required to stick to the parameters set out in law, and overall I am satisfied that those who are genuinely eligible for ACC-funded elective surgery are getting it."
