Q&A
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John Slamin
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Slamin has been involved with knee-implant product development for more than 30 years. In 1974, after graduating from the Wentworth Institute of Technology in Boston, he went to work for the research and development arm of Johnson & Johnson’s then-new orthopedic division. He oversaw product development activities for it from 1982 to 1997, a period that produced the PFC Total Knee System and the Sigma Total Knee System, among other things. For outstanding R&D achievements, he received the Johnson Medal. He also worked with Clifford Colwell, MD, of Scripps Clinic (La Jolla, CA) to design the first fully integrated and electronic implantable knee. He lectures extensively on knee-design and biomaterials issues.
ConforMIS, formed in 2004, has developed a line of comprehensive minimally traumatic, patient-specific knee implants and instrumentation to address all stages of osteoarthritis. Its innovations include implants that are precisely sized and shaped to match the 3-D topography of the patient’s anatomic bone surfaces and disposable instrumentation that simplifies and improves the surgical process. Slamin spoke to Med-Tech Precision Editor Erik Swain in February.
Q: What are the biggest advancements you have seen regarding knee implants in the more than 30 years you have worked with this technology?
John Slamin: Certainly in the 1980s it was the application of computer engineering programs for both design and manufacturing. That paved the way for all of the advances that have come since then. I started with it in 1979-80, when I was with Johnson & Johnson. When computer engineering applications came along, it made sophisticated engineering strategies such as finite element analysis more possible, and that had an impact on the industry. In the last 10 years, rapid prototyping has had a real impact not only on medical devices but on all manufacturing industries.
Q: What has caused the increased demand for knee replacements?
Slamin: The single biggest factor would be that knee implantation was shown to be a highly successful and repeatable procedure. Survivorship is extremely good, with a rate of 90% over 10 years. Surgeons and patients are now more comfortable with the procedure. And the patient population is growing because the minimum age limit has dropped. The baby boomers are starting to come into that patient population, and they are a very large group. We anticipate an even bigger surge in procedures over the next 10 years.
Q: When designing a total knee system, what are the most important things to take into account?
Slamin: Obviously you need materials that are biostable and biocompatible, and you need to fit the implant to the patient properly. In the orthopedics industry there is a major focus on coming up with designs that are a better fit for the patient population. You also need to learn about the wear properties of the materials you are considering. That is a very important design element because it relates to the life of the product.
Q: What materials tend to work best for giving patients the best replacement knees possible?
Slamin: The proven technology is to use cobalt chrome on the knee femoral component, to use ultrahigh molecular weight polyethylene (UHMWPE) that does not suffer from oxidation, and to have another layer between the polyethylene and the tibial tray that is made out of highly finished cobalt chrome as well. It has been 30 or 40 years of reliance on these materials. The cobalt chrome component is a relatively cost-effective material to use. It finishes extremely well. UHMWPE has been the standard material since 1962. For the metal tibial plateau, you can use stainless steel or titanium, but the market is shifting to cobalt chrome, because you can finish it with a very high polish. And that can reduce the amount of wear that occurs between the polyethylene tibial insert and the tibial tray.
Q: What are some of the challenges faced when designing knees for those with osteoarthritis?
Slamin: Every patient is a little bit different. Trying to force a standardized approach upon an infinitely varied patient population is technically challenging. One thing to take into account is that the mechanism between the tibial insert and the metal tray must be a secure fit that eliminates movement. You have to take into account the fixation of the components.
Another challenge is that traditional total knee replacement has worked well for older, less active patients but does have drawbacks for younger osteoarthritis patients. A young, active patient who gets a total knee replacement is at greater risk of more invasive revision surgery later in life. That is a problem that ConforMIS is trying to address.
Q: When did computer modeling start becoming used for knee design? Is everyone doing it these days?
Slamin: The very first applications were around 1979-80. Very early on in my career, I applied computer design technology to knee implants. It used to take weeks to do a design. Now we can do it in hours.
There are a few different systems out there, and all are relatively equal in terms of how they are preferred across the industry. Some are geared for larger corporations, others for smaller ones. But all are easy to use and offer a lot of flexibility. It’s a very, very competitive market.
Q: What can designers do to minimize the complexity of the surgical procedure required for implanting an artificial knee?
Slamin: The best way to simplify the surgical procedure is not necessarily in the implant design, but in the design of the tools surgeons use to install the implant. A great deal of time is spent engineering the tools. Many times, a surgeon will make a decision on which implant to use because he has a preference on which related instruments to use. In the world of standard implants, the major implant offerings all tend to perform well, regardless of which one you use. The instrumentation could well be the difference in what system a surgeon chooses. We think there is potential in rethinking both implants and instrumentation to make the combination work better.
The large companies design instrumentation systems that tend to be highly flexible. Surgeons have a preferred sequence to do the steps of the procedure. So the instrumentation system must be flexible enough to accommodate all the potential sequences. So you end up with enormous instrumentation systems that are very, very expensive.
There is a trend to move to a system with some disposable instrumentation. The advantage will be in cost. The problem that a lot of the larger corporations have is that because they apply standard implant sizes within their implant systems, many of them have instrumentation in their kits that cover implants of all different sizes. For example, if an implant from Stryker or Zimmer has 12 sizes, the kit must include tools for all 12 sizes. So you need 5-10 instrument trays in order to cover all of the possibilities. A typical instrument set can cost $25,000, but the companies do not sell those. They consider that cost a capital expenditure, and only charge for the cost of the implants. So the trend toward disposables might be difficult for the larger implant companies to implement effectively.
The opportunity ConforMIS sees is the chance to radically minimize complexity by designing implants and instrumentation that work together to reduce the number of steps, the number of bone cuts, and the variability that a surgeon faces in the OR. If we can make a specific implant for a specific patient, we can reduce the cuts required to fit the patient to the implant, and we can eliminate the need for a lot of the flexibility that current tool sets are designed to accommodate.
Q: The knee-implant business is a crowded field. What does it take to set a company apart?
Slamin: The true innovation always comes from small companies way out in left field. You can get creative with distribution models when you’re smaller. That’s all part of innovation as well. You can look at what the big companies do and pick and choose what’s right for you.
Q: What innovations related to knee implants might we see in the future?
Slamin: New materials will continue to develop. Something with better wear characteristics than polyethylene will come along. There will be different ways to use computers in design. One big trend will be computer navigation systems. An enormous amount of money has been spent on these, but they have not yet reached their full potential. We have to think about how to apply them in nonconventional ways. Some doctors don’t want to deal with computer systems in the OR.
An alternative approach, for example, is to “navigate” the surgical instruments presurgery. Rather than using computers in the OR to get precise digital readout of the alignment, we can use high-resolution imaging data to get the same information. You can then design instrumentation that is shaped to reproduce that precise alignment in surgery via patient-specific cutting guides. It offers the benefits of navigation without the expensive computer system in the OR. We see lots of potential for that type of approach in the long run, because it has so many advantages versus buying dedicated, expensive computer-assisted navigation systems that, in the end, actually increase complexity and OR time.
