Treatment injury claims should get accepted more often after a High Court ruling, lawyers say.

A landmark High Court ruling means ACC will be more likely to accept claims for injuries resulting from treatment by a health professional, lawyers say.

On Friday Judge Peter Churchman found against ACC in an appeal over two District Court rulings on treatment injury cases.

One case involved a woman who had a stroke as a result of surgery on a brain aneurism and another was a woman was left with incontinence and a numb leg after spinal surgery.

CHRISTEL YARDLEY/STUFF ACC argued the injuries of two claimants were an "ordinary consequence" of treatment but the High Court disagreed.

In both cases ACC argued the injuries were an "ordinary consequence" of the treatment and therefore they did not qualify for cover.

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But Churchman found ACC had not adequately shown this to be the case and in his ruling clarified the way these claims should be assessed in future.

Supplied Brittany Peek, lawyer from John Miller Law said a landmark High Court ruling means ACC will be more likely to accept claims for injuries resulting from treatment by a health professional.

ACC had relied on medical opinion that there was a significant or increased risk of the complication in deciding to decline cover.

Lawyers representing the claimants argued that ACC should have to prove a complication was "ordinary and expected" and that clarification was needed.

Churchman agreed and said ACC needed to show the problem was more likely than not to occur, or would likely happen in at least 50 per cent of cases.

John Miller Law lawyer Brittany Peck, who represented one of the claimants said the appeal by ACC gave them an opportunity to test this issue in court.

"It's significant because it clarifies what previously had been a somewhat unclarified part of the treatment injury legal test."

In practice it the ruling would make it harder for ACC to turn down treatment injury claims.

"Hopefully now with the High Court clarifying that .... the ACC claims unit will now have to apply that threshold and more people should have cover even if they haven't got lawyers who can assist them in taking it to court."

In 2005 the Injury Prevention, Rehabilitation, and Compensation Act 2001 was amended to give wider access to cover for personal injuries from treatment provided by a health professional - known previously as medical misadventure.

Previously cover was only granted for medical errors where the complication was shown to happen in one per cent of cases.

The amended legislation replaced medical misadventure for treatment injury defined as a personal injury suffered during treatment by a registered health professional and "not a necessary part, or ordinary consequence, of the treatment".

An ACC claimant said the Corporation received the ruling on Friday and had not considered it in detail yet.