The number of New Zealanders implanted with a faulty hip joint who have had it removed has jumped.

Hip registry figures show that 23 per cent of those implanted with the DePuy ASR conventional total hip had the device removed.

Previously available data showed 7 per cent had been removed by December 2010.

Manufacturer DePuy recalled the prosthesis in August 2010 after data from Britain showed a 14 per cent fail rate after six years, well above the usual rate of 3 or 4 per cent.


Also withdrawn from the market was the ASR hip surface replacement device - the ball of the patient's hip is resurfaced with metal - which had shown a similar failure rate.

Both devices use a metal cup made of cobalt and chromium which is alleged to contain design flaws.

Ten per cent of the surface replacement devices implanted in New Zealand have been removed.

But NZ Orthopaedic Association president Bryan Thorn said a lot of these hips probably did not "strictly, medically need revision".

He suspected many were removed because patients did not want them because of the recall or found they had elevated blood readings for cobalt and chromium.

Worldwide 93,000 ASR devices were implanted, 507 in New Zealand. A group of New Zealand patients is taking legal action in Britain against the manufacturer.

Mr Thorn said the issue focused attention on regulation of medical devices.

"I am concerned that we have been working in a fairly under-regulated environment for a long time in this country and this issue is making us take note and say, 'hey, should we be tightening up on devices and implants'."

The ASR resurfacing product was rejected by the United States, but was able to be sold elsewhere, including in New Zealand.

The ASR total hip replacement got into the US market through a regulatory loophole that enables products deemed similar to ones already on the market to be approved without extensive trials.

The European approval system has recently been criticised as lacking transparency and ripe for collusion.

Mr Thorn said a lot came down to individual surgeon responsibility about what they chose to use and how they addressed that with patients.

"We [the Orthopaedic Association] are not a police force.

"We can only remind members to be responsible in using implants and devices [particularly] if they haven't been through the regulatory approval process in the US."