Designs on Implant Innovation

An orthopedic implant is only as good as its design. But many factors can influence the design of an implant or even a component within the device, including cost, materials, regulatory requirements and patient demographics. In the last decade, innovative surgical techniques and advances in technology have played an important role in shaping new implant designs that are now becoming the standard of care among orthopedic surgeons.

To gain some insight into the thought processes behind implant design and help identify the trends shaping the sector as well as the challenges currently facing companies, Orthopedic Design & Techology spoke to several industry professionals over the last few weeks.

They included:

•  Steve Maguire, general manager at Orchid Design, a division of Shelton, Conn.-based Orchid Orthopedic Solutions, a contract design and manufacturing firm serving the orthopedic, dental and cardiovascular markets.

•  Josh Sprague, vice president of Hoosier Inc., a full-service spinal contract manufacturing company based in Corona, Calif.

• Jeffrey Kapec, a principal and executive vice president of Tanaka Kapec Design Group Inc., a Norwalk, Conn.-based design consultancy.

• Anand M. Vora, M.D., an orthopedic surgeon in Illinois who also teaches orthopaedic surgery at both Northwestern University Medical School and the University of Illinois Medical School. Dr. Vora also is a member of the American Academy of Orthopaedic Surgeons.

Editor’s note: This is the first of three installments of ODT’s roundtable discussion with these professionals about implant design.

ODT: What are some of the latest trends in orthopedic implant design?
Steve Maguire: The latest trends in orthopedic implant design are migrating from innovation to cost and outcomes. The healthcare environment is the driver of this shift and doing things faster, simpler and at a lower total cost is the direction we see. As such, proven implant designs are being replicated and lower manufacturing costs are the driver. Instrumentation that is easier to use and helps a surgeon with repeatable surgeries is also a focus. We have seen investments in navigation, both manual and navigated with computer assistance.
Josh Sprague: Interspinous Process (ISP) devices, stand alone devices, lateral lumbar cages and design for manufacturability has been all the rage over the past year. The most frequent new device that we’ve seen in 2010 are ISP devices. ISP implants distract the foramen and are thought to unload the intervertebral disc. A major benefit is the minimally invasive approach to spine repair due to the proximity of the spinous process to the skin. They may be implanted after a mild sedative and local anesthesia with the patient often going home the same day of the procedure. One of the major target markets for these devices are the elderly since they may not be able to endure the more invasive typical fusion procedure. The cost and complexity of these devices varies widely across the industry.

Stand alone devices launched onto the market in 2010 and we continue to see more and more new styles coming on board for 2011. Stand alone devices eliminate the requirement for supplemental fixation and anterior plating systems. The benefit to these devices is often the reduced cost of the overall implants required for surgery, a less invasive procedure, blood loss and recovery time. It’s an exciting technology to Hoosier but they often do pose significant manufacturing challenges due to the complex geometry and tolerance requirements. Fortunately Hoosier’s investments in high tech equipment have played a major role to ease the burdens of manufacturing challenges on these devices, making complex geometries previously near impossible to make consistently, now fairly easy.

Lateral lumbar cages similar to Nuvasive’s XLIF have been quite popular as of late. The typical diagnosis is to treat leg or back pain that has been caused by degenerative disc disease in the lumbar spine. The key marketing points of the XLIF procedure are minimal blood loss, smaller incisions, minimal post-operative discomfort, minimal tissue damage and a faster recovery time. One of my family members had the XLIF two years ago and it was quite impressive to see him return to golf game, almost better than before I might add, within six months.

The last big push in 2010, and we certainly expect a big push in 2011, is design for manufacturability. All of our clients are being forced to find ways to reduce cost and the reality is that cost reduction rolls downhill. We saw this coming years ago and have invested in high tech equipment to help, but equipment can only do so much. Sometimes parts are just simply tough to make! In the past some customers didn’t care about the difficulty because their products were innovative or the added complexity gave them more security with patent protection, marketability, and sometimes cosmetic appeal (implants should look good, who would want to implant an ugly implant?). Now the name of the game is price, simplicity, and how many parts can you get me quickly. It’s a win win for the OEM, patient, and the vendor when the parts are easier to make.
Jeffrey Kapec: The industry is being driven by changes in the marketplace, which is particularly interesting for the orthopedic industry. Baby boomers like me are beginning to go through the phase where they’re feeling the physiological changes in their bodies. We are beginning to sense that we don’t have range of motion. We now are feeling minor pains or major pains. But unlike our parents and grandparents, we’re not willing to compromise quality of life with pain. I’m thinking of the way my grandmother looked at 60 years old. As a little boy, I thought she was ancient. I thought she was part of the pyramids. At that age—60—she did look like she was part of the pyramids. That’s the way that generation aged. It wasn’t a question of can I do something about it. It was a question of can I stand up today? And they tolerated it. They accepted it and they died with it.

Our parents began to make changes. Some were more forthcoming and said, ‘I want to make a change and get this hip implant. I don’t know what it means, it sounds scary to me but we’ll do it.’ The implants were generalizations at that time. They were the best technology that could be afforded, given all of the tools that orthopedic engineers had at that time. Now we go into the baby boom generation and we’re seeing that we are more willing to get over the pain and get back to quality of life, which means all of the sporting activities, all of the extra-curricular activities that we anticipate and the continuation of our career path (we’re no longer retiring at 60).

People in the Baby Boomer generation are being driven to go in and get the implants so they can continue a normal life. That is a huge market and it’s driving the orthopedic sector. We’re also requesting better outcomes from these surgeries. We want to be able to walk sooner, walk better and not compromise the way we walk or the way we move. Orthopedic companies are well aware of this.

Then we add to that all the new science information coming in—the growth factors that we’ve begun to appreciate. Many years ago we worked on a project for Stryker with bone cement and now it’s one very important component of their product portfolio. Today bone cement is used for implants as a last resort for a compromised patient that can’t expect to have growth factors. The direction of the implants is to specialize, customize or more compartmentalize the implants that are designed for different physiological groups.

You add one other component. We now have modeling tools. We can model in the anthropromatric motioning gait and all of the anatomical dynamics into the design of an implant. We couldn’t to that as effectively 20 years ago. All of these things—including the science and the technology and the growth factors—are creating implants that are amazing compared to what they were 40 years ago. We also added one other dimension—the surgical technique now is improving so much that the invasive qualities of surgery—the way the techniques are performed have greatly changed.

The latest trends are these different sectors of growth factors that are now being applied to surface coatings of implants; compartmentalizing of implants for the anatomical group—female, male, size, gait; computer modeling that enables us to better understand forces that are applied to the implant and to the anatomical site; and improvements in surgery and surgical techniques. Some of the implant companies are now beginning to talk about customized implants using these new metal deposition methods where they actually grow an implant for a patient. There are technologies that allow metal form to be built much as an SLA would be built. Say you do a computer model of a part, maybe it’s an implant for a hip, they could actually build that part specific for that one application. The part is built exactly to the computer model, it’s not machining. The machining is secondary operations, the primary build process is the growth.
Dr. Anand M. Vora: One of the things that we’re trying to do overall is design implants that have a greater longevity and are more comparable to the natural tissues (in a simplistic way, the metals are more compatible with the bone, for example, so it mimics more natural bone type of healing). Nowadays some biologic devices such as growth hormones and other things are classified in certain categories as implants. I think is interesting in particular that the whole concept of implants is taking on a biologic meaning, not just the traditional metal meaning because that’s where most of the interesting new innovations are—the concept of biologic-type implants that mimic more natural native type tissue and incorporate growth factors and other kinds of biologic principles.

ODT: What new materials are being used in orthopedic implant design and what benefits do they provide over other, more traditional substances?
Sprague: We haven’t seen a major change in the status quo. Invibio’s PEEK Optima is still the major player in the market, but other PEEK alternatives have certainly popped onto the radar. We’ve seen a few customers use the other materials for research and development purposes and some intend to launch new products with the alternate material, but so far the major player is still hands down Invibio. As far as technical benefit, there are some pros and cons with the other materials such as a minor increase in tensile strength, flexural strength and elongation (some more, some less). The main attraction to the other PEEK alternatives has largely been price over mechanical properties. PEEK is an amazing polymer often known as Teflon on steroids due to its high lubricity and strength just to name a few. In the implant space peek is often an overkill of material from a mechanical perspective, but it’s not just strong, its biocompatibility, absorptive characteristics and machinability is also impressive, hence why the material has done so well.
Kapec: Ceramics is certainly one of the things that we’re looking at, and also a combination of ceramics and polymers. The plastics industry is getting actively involved in trying to come up with materials that wear better and have less friction, and have less biological reactions. Titanium, chrome, and stainless steel are still the dominant materials. But I think we’re going to see changes in those areas and also in this concept of growth factors, getting materials with coatings that induce bioactivity. There’s alot being done in the biologics area. With biologics, we’re talking about a whole new approach to materials technology. What kinds of materials are we going to surface finish? Where are we going to apply these materials? How are we going to use them? For example, the stem of a hip is being treated now with materials that induce bone growth.

Bone cement was often used to fuse or to join the implant to the bone, and that now is considered when you don’t have any other alternatives. The industry is now looking at more of a unification of the implant to the bone structure – osteoconductive, osteoinductive. The same thing is true in lower spine surgery, where you’re doing a fusion and you’re putting in a lot of structural support to keep the vertebrae spaced, to take the pressure off the nerve root. But the objective is to get the body to produce bone structure to create that bridge biologically. There’s work being done—we worked on one product with a company to use growth factors from the patient in conjunction with bone and plasma rich blood to accelerate bone growth in the spine following the last stages of a fusion surgery. This area—biologics—is moving very, very quickly.

Before it was more of a mechanical approach to orthopedic design. You used a mechanical fixation. It’s still mechanical now, but we’re using the biologics of the body to create that mechanical fixation in a surface that’s created to accept that bone growth and can make sure it becomes unified to the bone. That’s where the science is going. That area is extremely fertile right now. Other materials would be all ceramic implants—they are in the vanguard still, but they are becoming more interesting to orthopedic companies because they last much longer. The wear resistance is high and it has an extremely high mechanical strength too. And they are ultra-hard surfaces. The technology is still being perfected, but it will become better understood, better processed and more affordable. Because ceramics is still such a small segment, the production costs are fairly high.

The situation with ceramics is analogous to LCD screens. When you looked at an LCD screen 15 years ago, it cost $4,000, now it costs $800. It’s a matter of once you begin to ramp up and perfect the manufacturing process, these new exotic materials become less exotic or they become more commonplace. Ceramics have been around for quite some time. The first ceramic experiments took place in the 1970s, and they were using an alumina ceramic. But that material was not as suitable for the body. Now some of the new ceramics are changing, they’re coming in with much better results. The mechanical strength is much better and the ceramics now are built as composites. There are still some issues with failure rates, but right now there are some ceramic hips approved by the FDA and they are in the market. There are still some bugs to be worked out. But here’s the rationale: we have a 40-year-old man whose hip is degenerating. And he has kids. And he wants to live through that lifespan of that stage with his kids and he wants to be active. So if they put in an implant and they see wear factors after 15 years, he’s going to have to go back in for revision surgery. Well, he doesn’t want to do that. He wants to be able to go 20 or 25 years before he may have to consider revision. And they’re looking at ceramics as one of the options that would allow that life expectancy and allow active use.
Vora: We’re using different types of metal alloys that are more compatible with the body and more compatible with bone, as compared to traditional metal alloys that were less compatible. We’re using implants that are sometimes lower profile so the implants are less prominent, they’re more minimally invasive and they cause less problems. The plates and screws, for example, do not need to be removed after a bone is healed because the implants are much more compatible, much smaller, and have a much lower profile. They almost become in a true sense of the word “part of the patient.”

There’s also devices called bone morphogenic protein – they are really biologics that are being classified by the FDA as implants. Platelet-rich plasma is a really hot topic right now, and it’s something I think is very interesting. That involves taking platelet healing cells to initiate healing in all phases of treatment.
Maguire: We haven’t seen too many changes in the material options over the past few years. Certainly PEEK is being used more widely and becoming more available from multiple suppliers. We have also seen more use of nitinol that has unique material properties and demonstrated biocompatibility.