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Newcastle University’s bioengineering team has made a bid for some of the credit in helping to persuade Johnson & Johnson‘s DePuy Orthopaedics unit to recall its Articulating Surface Replacement (ASR) hip prosthesis from the market.

The researchers,  led by Dr Tom Joyce, began investigating the ASR hip prosthesis as far back as February 2008, and discovered a number of failings in the design of the implant and offered an explanation into how and why the metal joint was being worn away, releasing high levels of toxic metals into the patient’s bloodstream. The subsequent recall means that thousands of patients – estimated at 93,000 worldwide, are being recalled in an effort to determine the extent of the problem and offer support to those who have been left with the crippling side-effects. According to DePuy, “very few” of the ASR devices remain on the worldwide market, following the company decision in 2009 that it would be discontinuing the ASR system as a result of “declining demand and the intention to focus on the development of next generation hip replacement and resurfacing technologies that best meet the needs of surgeons and patients.”

Joyce explained: “The thinking was that a metal-on-metal ball and socket joint should be far more effective and hard-wearing for patients than the older style metal-on-polymer system where the softer polymer tended to wear away quite quickly, releasing particles and eventually causing the artificial joint to fail. What our research showed was that if the ball and socket were not perfectly aligned then the metal wore away quite vigorously – the initially ultra-smooth surfaces roughening and then grinding away against each other – to release nano-sized particles into the body that were then absorbed into the bloodstream and tissues, causing far greater damage.” According to Joyce, only in a minority of cases were the joints actually functioning correctly.

Concerns first began to arise when a number of patients reported groin pain, some not long after their arthritic hips had been replaced with ASR prostheses. Working with orthopaedic surgeon David Langton, based at North Tees University Hospital and now working towards a PhD in Bioengineering under the supervision of Joyce, the NU team studied over 100 explanted hip joints sent to them from across Europe. Blood tests revealed high levels of cobalt and chrome ions in the blood stream of ASR patients. The ASR is made from cobalt-chrome alloy so this implicated the artificial hip. Using a “state-of-the-art” machine, the team studied the surface of the artificial hip joints and found that instead of being highly polished with a mirror-like surface, the failed devices had become roughened. This caused the lubrication of the joint to fail so that, with each step, the patient was producing relatively high volumes of metallic wear debris.

The ASR device formed part of a class of large diameter, monoblock hip resurfacing and replacement devices often selected by surgeons for younger patients who may benefit from a more stable device that can reduce the chances of dislocation after surgery. The DePuy ASR hip resurfacing system was introduced in 2003 and is only approved for use outside of the US, whilst the ASR XL acetabular system was first launched in 2004 and has been available worldwide.

DePuy, like its peers in the industry, will look back on this chapter in the history of hip replacement and hope to learn its lessons. For one thing, sometimes a development that appears to be successful and the answer to a major problem may not necessarily work out all so wonderful in reality over time. The industry has also had to trade off the benefits of technology with its failings, but recalls such as those from DePuy and Zimmer are inevitably going to make it much more difficult to convince surgeons and and potential patients that future technologies won’t suffer the same fate in the future. It is also likely to lead to much more stringent and expensive clinical trial programmes, and further regulatory scrutiny.

Thanks to Lawrence Miller for this post, Lawrence is the medical newsletters team leader and managing editor of Medical Industry Week and Orthopaedics Business

More to come this week, drop back soon, thanks, Paul.

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