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Orthopedic Coatings Expected to Rapidly Evolve, Says Surgeon

Dr. Stuart B. Goodman is the Robert L. and Mary Ellenburg Professor of Surgery, and Professor in the Department of Orthopaedic Surgery and (by courtesy) Bioengineering at Stanford University. His clinical research interests center on the outcome of surgery to treat arthritis, including primary and revision total joint replacement, juvenile arthritis and osteonecrosis of the hip and knee. His basic science interests center on biocompatibility of orthopedic implants, inflammation and musculoskeletal tissue regeneration and repair. Search the internet for biologic coatings, and his research is one of the first results.

What important roles do biologic coatings play in orthopedic implants?

Dr. Goodman: The first thing to know about biologic coatings is that work needs to be done to truly understand the effectiveness and possible risks of regularly incorporating them in orthopedic implants. However, we know that the potential is there to diminish some of the existing risks of implants.

For example, we’re hopeful that biologic coatings may reduce the risk of infections associated with orthopedic implants. There is also potential for coatings to treat infections internally. When it comes to revision joint replacement, specifically when the host bone or biological environment is suboptimal, it may be possible to change the surface with coatings or other treatments that could help with osseointegration. But before the scientific and medical communities can definitively make these claims, we need more comprehensive studies using the right technology with optimal controls in order for coatings to be proven as both safe and effective, as well as cost effective.

Do you think that the science behind biologic coatings for implants is widely understood by device companies, and by your surgeon colleagues? What should these two groups know about each other?

Dr. Goodman: I don’t believe that the science behind the benefits of biologic coatings is widely understood by engineers or surgeons, because enough research hasn’t been performed on the subject. About 20 years ago, we all thought the development of biologic coatings was great and that we should coat all of our implants with (hydroxy)oxide, but it never really caught on much in the U.S. There were trials and studies, but now it’s not really that popular; not even worldwide.

Several years ago, when I was a member of the Biological Implants Committee of the American Academy of Orthopaedic Surgeons, we told more than 25,000 surgeons from all over the world that there have been a lot of ups and downs in biologic coatings. From the initial enthusiasm for biologics 10 to 20 years ago to seeing some of the downsides with complications and adverse reactions, the simple truth is that there has to be a great deal more research, preclinical research to really justify the cost and the efficacy and the safety for doing all these innovations.

Orthopedic surgeons like to use new technology, patients ask for new technology and manufacturers like to put forth new technology to stay competitive. All of us want to provide the best possible care for patients, but a lot of new technologies that might be contemplated need to be built on sound principles in the preclinical arena before their use can be more widespread. Some of the new technologies have already been introduced with insufficient clinical and preclinical data support. They are also very expensive, moreso than a standard implant.

In that regard, FDA is starting to strengthen regulations for manufacturers of other biologics that are being injected into patients, like into joints to treat arthritis. In my opinion, FDA is doing the right thing because patients are sometimes so desperate for something that will make them feel better that they’re willing to try anything, and that includes treatments that aren’t as evidence-based as we would like.

We understand that you’re interested in antimicrobial coatings, specifically. What opportunities and challenges do these coatings present?

Dr. Goodman: One of the most obvious potential benefits of biologic coatings is to prevent infection. In general, infection is one of the leading causes of revision surgery in total knee and total hip replacement. As patients get older, immune systems change and surgeons are performing these procedures on patients with several other medical challenges. They may be living with cancer or lupus or any number of serious illnesses that can weaken immune systems. That being the case, we need to think of ways to combat not only acute infection in the perioperative timeframe, but in the long-term.

Over half of the infections in patients are now surfacing more than a year after the device has been put into place. Hip and knee replacement devices are now lasting 20 years or more, and infections can surface literally at any time. Antimicrobial coatings could be part of the solution for orthopedic devices to resist infections over a long period of time, but there could be other strategies worth considering as well.

What happens six months later, a year later, even 10 years later when someone’s immune system is changing and they are subjected to different bacteria? It’s not just about getting patients through the perioperative stage; we need to find ways to protect the environment exposed to the medical device and prevent it from harmful changes throughout the life of the patient and the implant.

What trends do you see in the coating of orthopedic implants? Do you foresee these continuing for the next five years? Ten years?

Dr. Goodman: There is so much work that still needs to be done in the area of coatings in orthopedic implants that it’s difficult to define anything as a trend. In my opinion, we’ve only begun to scratch the surface with regard to the research and testing needed before these coatings could become commonplace. In the interim, we need well-defined goals for what we are trying to accomplish both short-term and long-term. Research needs to be conducted for patients who will live long and active lives that will be continuously subjected to different forms of bacteria. We need to learn how coatings will react to these bacteria over time, and how these reactions may impact the health of the patient.

I also believe that the technology will change very rapidly over the next several years. I know there are already groups at work on coatings that may eradicate the presence of bacteria both long-term and short-term. There are other questions like whether or not the eradication of one type of bacteria could possibly cause other forms of bacteria to multiply or mutate in the environment. Right now, we just don’t know.

What coating technology still in the experimental phase do you find of interest?

Dr. Goodman: I believe one of the most important and interesting technological developments in the realm of orthopedic devices is the creation of multifunctional coatings. It would be optimal to create coatings that can safely integrate with the body while preventing and fighting infections long-term. Rather than single-functional coatings used in the past, such as hydroxyapatite or antibiotic-coated rods with bone cement, we’re going to have to think more efficiently and creatively to effectively accomplish a multitude of goals. As the technology continues to evolve, I believe it will soon reflect that manner of thinking.

Kim Snell
is an ORTHOWORLD Contributing Editor.