By the time DePuy Orthopaedics was forced to recall two of its hip replacement systems, the DePuy ASR XL acetabular system and the ASR hip resurfacing system, because of a higher than-normal failure rate, the devices had been used in more than 93,000 hip replacements. They were approved by the Food & Drug Administration (FDA) in 2003 but the FDA had received more than 300 complaints about them in two years, including loose hip cups, dislocations, bone fractures, soft tissue masses about the hip caused by metal debris, allergic reactions, and permanent muscle and tissue damage.
In a separate development, last year it was announced that the UK’s Medicines and Healthcare Products Regulatory Agency was to review the operations of some 40,000 metal-on-metal hip replacements, amid fears these implants could cause soft tissue masses about the hip resulting in bone, muscle and ligament damage.
Thankfully, such recalls and complications are relatively rare but, with an estimated 152,000 hip replacement surgeries being performed in the US in 2000, (a 33% increase from 1990) and the number of hip replacements expected to grow to 272,000 by 2030 as the baby-boomer generation ages, how device manufacturers can improve artificial joints – and reduce failure rates still further – are becoming issues rapidly moving up the priority list.
"Arthritis is the most common medical problem of older Americans. Baby boomers are getting older yet want to remain active and lead a life without physical restrictions," notes Dr Mary O’Connor, associate professor of orthopaedics and chair of the department of orthopaedic surgery at the Mayo Clinic in Jacksonville, Florida.
"They do not accept disability in the way that some previous generations have. The obesity epidemic is also fuelling problems with arthritis. The heavier you are the more stress you place on your joints and the more likely it is that arthritis will develop," she adds.
The average lifespan of metal joints is about ten to 15 years, meaning that physicians have been reluctant to implant them into younger patients but, against this backdrop of patients wanting to remain fully active, living longer and the most obese possibly needing surgery younger, the longevity and reliability of joint replacements are growing issues.
There are alternatives that are being developed. Ceramic-on-metal joints, for example, can reduce the wear and tear on artificial joints up to tenfold. Medical centres such as the Columbia University Medical Center have also been among those investigating ‘biologic’ alternatives – or devices that use or contain biological processes – including the use of biomaterial scaffolds upon which cells can grow and build.
Purdue University, at the University of Alberta, has been investigating how ‘nanotubes’ that assemble themselves using the same chemistry as DNA might create better artificial joints and other body implants. Bone cells called ‘osteoblasts’ attach better to nanotube-coated titanium than they do to conventional titanium used to make artificial joints, the researchers concluded in last April’s edition of the journal Nanotechnology.
Ultimately, the key problem is that device companies, scientists and physicians have yet to find the perfect solution, points out O’Connor. "We still have not found the ideal bearing surface, and that is what everyone is trying to do. People are keen to try out new products in this area, but what is imperative is that new products are thoroughly tested to make sure there are not unforeseen problems. Of course this is not easy to do."
She notes that there are issues around the field of biologics, which has the potential in time to offer cures for arthritis so that we will no longer need replacement joints. There is a lot of work going on around how we might be able to prevent arthritis in the first place or how we can slow its progress or even how we might be able to reverse it.
"So what we are really seeing is a health crisis with arthritis that is not really being adequately addressed," she warns. "There is an argument that we need to be investing more in biologics and in treatments designed to prevent and reverse arthritis. But realistically, biologics is not going to be the answer for at least another 15-20 years, perhaps ten at the absolute earliest.
"So joint replacement surgery is not going to stop happening at least for the near future. Ideally, of course, we will find a cure for arthritis and no longer need to replacing joints but I do not see that happening anytime soon," she continues.
When it comes to the issue of joint replacement failure, O’Connor argues that two inter-linked courses of action are required. The first is that the US needs an independent national total joint replacement registry, something that already exists in countries such as the UK and Canada and, she suggests, was part of the reason why the DePuy issue was identified relatively quickly in the UK.
The orthopaedic community has been working on the development of such a national registry. The American Joint Replacement Registry has been established, making some progress towards this (see the panel above) but O’Connor argues that more still needs to be done.
"In the Johnson & Johnson case for example – which is not an isolated situation because this has been seen with other implants made by other companies – having a national registry in the UK meant it was possible and much easier to identify when there was a problem with an implant. Without the data that was gathered by the registry, the problem may not have been identified until much later. Having that level of transparency and access is better for patients, better for surgeons and better for the healthcare system," she suggests.
Second, what’s also required is more openness and transparency from device manufacturers themselves, something that can be challenging given that, in a highly competitive environment, it is only natural that manufacturers might be reluctant to publicise failures or complications unless they absolutely have to.
"Of course, the people who are involved with the design and testing of these implants are doing things with the very best of intentions; they quite obviously want to create a product that is better and superior to what is otherwise available. So there is no malintent involved. But you can sometimes get unanticipated developments," explains O’Connor.
"What we would like implant companies to be is as transparent as they possibly can if concerns arise regarding an implant. Of course, we will need to define what constitutes transparency and try to provide some type of mechanism where such transparency can occur without the threat of inappropriate litigation. I really think it would serve patients, manufacturers and surgeons better if there were more transparency." There could, for example, be an accreditation system for device manufacturers and devices so that everyone would know where they stand.
"What we should also be looking at is more early warning systems for identifying implants that are not performing as they should be. I personally favour a partnership between the professional medical societies, implant manufacturers, insurers, the government and patients. This is the model that the American Joint Replacement Registry is using," she adds.
"My personal bias is that when something goes wrong everyone turns to the government and says ‘how could you let this happen and why are you not fixing it?’. But governments work slowly and not necessarily that efficiently. So I believe responsibility for the process of monitoring implants and setting up detection and early warning systems to detect failures should be the responsibility of multiple stakeholders, not just one entity.
"The more diversity that we have in the monitoring teams, the greater the pools of knowledge, the better able we will all be to make effective recommendations."