On the Leading Edge: Improving Artificial Joint Performance
"Osteoarthritis is a degenerative disease that mostly affects the cartilage, the slippery tissue that covers the ends of bones in our joints," explains Kantor, whose specialties include hip and knee replacement surgery and minimally-invasive procedures for the hip and knee. "Osteoarthritis causes healthy cartilage – which allows our bones to glide over one another and also softens the shock of physical movement – to slowly break down. This can be due to the aging process or wear and tear."
Aging Baby Boomers
Have you noticed pain and stiffness in your knees or hips occurring more regularly as you've gotten older? Does it get worse after exercise and when you put weight or pressure on your joints? Perhaps you've also noticed some swelling around your joints, and a limited range of motion. If you're experiencing these symptoms you may have osteoarthritis, the most common type of joint disorder.
"The good news is that there are a multitude of treatment options we can make available to them," Kantor says. These include non-surgical options like anti-inflammatory medications, cortisone injections, supportive devices such as braces and splints, and physical therapy. "For those with more advanced disease, there are surgical interventions such as joint resurfacing, where we shave away the diseased surface of the joint and 'cap' it with an artificial surface, and total joint replacement, where the diseased joint is removed entirely and replaced with an artificial implant."
The bad news is that osteoarthritis is progressive. "Though a lot of patients are able to successfully manage their arthritis for many years with non-surgical treatments, the treatments become less effective at controlling their symptoms over time," says Kantor, who is also an assistant professor of surgery at Geisel School of Medicine at Dartmouth. "Eventually, many if not most of these patients seriously consider joint resurfacing or total joint replacement, which is today the only cure for osteoarthritis."
"How Will I Know?"
One question that Kantor gets asked a lot is, "How do I know when it's the right time to have surgery?"
"I tell them that the logical time is when they've exhausted the other treatment options, and they feel that the level of encroachment of their arthritis on their daily activities is no longer acceptable," he explains. "For some patients, that means not being able to get up in the middle of the night and walk comfortably to the bathroom. For others, it's not being able to walk 18 holes on the golf course."
Coming to the decision to have surgery requires much thought and consideration. That's why at D-H, orthopedic patients and their families are strongly encouraged to use the Office of Shared Decision Making to help them through this process. "We send them a video and other decision aids to review before their visit," says Kantor. "This allows them to learn more about their disease and treatment options. They then come to our office better informed and surer about their treatment preferences. That makes our encounter more productive as we work together to find the treatment solution that will truly work best for them."
Recent media reports about the premature failure of one particular all-metal hip implant – a model called the ASR (manufactured by DePuy) that was investigated by the FDA and voluntarily recalled from the market – has raised public concerns about the risks and durability of artificial joints.
But, says Kantor, with its long track record as a specialty – modern joint replacement has actually been around since the 1960s – decades of research, and advancements in technology and surgical techniques, joint replacement is one of the most successful procedures performed today.
"Ninety-five percent of patients report high satisfaction with comfort and function and say they would do it again," he says. "And of the roughly one million joint replacement surgeries that are performed annually, on average only about one percent fail prematurely. Still, it's important to recognize that just like any other mechanical device, a hip or knee implant will eventually fail, and that even today a good life expectancy for an implant is about 15 years."
What happened with the ASR model, which began failing much sooner and at an estimated failure rate of about two and a half percent? Many contend that testing through clinical trials needs to be more extensive, and that the approval process for new implant designs needs to be more rigorous. Others point out that, unlike countries such as Australia, Great Britain, and Canada, the US does not have an orthopedic registry that tracks patient outcomes and could pick up on failure rates more quickly.
That makes research conducted by leading academic centers such as D-H all the more vital. For example, Kantor and his joint team partner, Dr. Ivan Tomek, have led a number of national studies to evaluate the safety and effectiveness of new implant designs. D-H surgical teams also have the unique benefit of being able to meet regularly with one of the world's foremost authorities on why artificial joints fail – Dr. Michael Mayor, who has been serving on an FDA advisory panel in Washington, DC that is reviewing the ASR case.
Mayor, who led a highly distinguished, 40-year career as an orthopedic surgeon at D-H, has also worked with metallurgical engineer John Collier, PhD, and other experts over the years at Dartmouth's Thayer School of Engineering to develop biomedical materials and techniques that have become industry standards for improving artificial joint performance. Their efforts have included reaching out to the international orthopedic community, inviting surgeons to send their explanted, failed implants to Dartmouth for analysis.
Many have answered the call. Over the years, Mayor has compiled the world's largest collection of retrievable implants, more than 12,000 to date (including all metal-on-metal models currently in the marketplace). "Some of them are stored in our lab," he says, "but the collection is so large now we've actually had to rent storage space in a warehouse. We do a rigorous analysis of each one that includes photography, computer-generated imaging, and other assessments such as those involving metallurgy and polymer science, as needed. We then generate a comprehensive report to send back to the surgeon."
The Right Stuff
As increased patient demand has prompted manufacturers to come up with more innovative designs to improve wear performance, more all-metal and all-ceramic implants have been introduced to the market. "They've worked well in the majority of patients, but some models like the ASR have been more vulnerable to breakdown," explains Mayor. "Though the surfaces are highly-polished – which proponents have thought would make them wear better and which looked good in simulator tests – these surfaces tend to wear down and generate debris, causing the implant to fail early."
"We've been able to establish, in a large 10-year follow up study, that a combination of soft and hard materials – a polyethylene socket with a metal or ceramic ball – has performed extremely well, with almost no complications and a 98 percent successful durability in patients," he says.
Not surprisingly, that is the choice of Kantor and his surgical colleagues at D-H.
"I feel very fortunate to be part of an academic health system where research is one of our missions, and where we have access to a wonderful resource like Dr. Mike Mayor and our other colleagues at Thayer. The knowledge we've gained from our research efforts has proved invaluable – both in understanding which implant designs can provide optimal wear performance, and in helping patients select the implant that will best meet their needs."