Back in the Game
Patient demand for high function andnear-perfect fit continues to driveinnovation in orthopedic implants andsurgical procedures.
Photo courtesy of Triangle Manufacturing Co Inc.
Jay Cutler officially entered the World of the Absurd at 3:02 p.m. on Tuesday, Nov. 29, 2011, barely a week after the starting Chicago Bears quarterback fractured his right thumb during a 31-20 victory over the San Diego Chargers.
On that day, at that precise time, Cutler’s broken first digit took to social media to confront its owner. The sassy finger, perhaps irritable from its injury, tweeted to the veteran passer: “The cast is HUGE! btw how u doin?”
Clearly not amused, Cutler fired back, “Less talking out of you and more rehab! Go find some ice or something.”
Showing its humorous side, the finger later asked (to no response, of course), “Thumb war anyone? O wait...”
At one point that afternoon (the obvious apex of the day’s digital lunacy), multiple Twitter accounts that claimed to be Cutler’s thumb had surfaced, slinging insults and accusing others of being the veteran passer’s lesser-known left thumb. By the end of the day, @jaycutlerthumb (the injured finger) was sparring openly with @JayCutlersThumb, an entity that—judging by the tweets—can best be described as a slightly more cantankerous digit.
Certainly, the tweets were a surprising change from an athlete better known for his abrasive demeanor and lack of charm than his sense of humor. In hindsight, the banter most likely was Cutler’s coping mechanism at work, helping him come to terms with the gravity of his season-ending injury. Consider the tweet he sent on Thanksgiving Day to update followers and Bears fans about his condition: “Surgery went great. Randy Viola is the best. My nurse isn’t bad either @KristinCav ;) Be back as soon as I can.”
Cutler may have had eyes for his nurse (perhaps she resembled his on-again, off-again MTV reality star girlfriend/fiancee Kristin Cavallari), but it was Viola with whom the quarterback truly was smitten.
Viola, 45, is a hand, wrist and elbow specialist at The Steadman Clinic, a world-renowned orthopedic facility with offices in Vail and Frisco, Colo. Viola’s approach to orthopedic surgery is a bit unorthodox (he considers it “responsible yet aggressive”)—he tailors implants to an athlete’s sport to help reduce healing time.
Viola’s fracture fixing game plan abandons tradition, trading the typical bulky splints and stiff immobilization measures for metal plates, screws and pins that set broken wrists or thumbs in carefully calculated athletic positions.
For example, he’ll fit a sterile baseball into a pitcher’s hand during surgery and bend a finger to simulate a certain grip, or he’ll meticulously position the wrist and thumb to help injured skiers regain their grasps on poles.
To repair the break at the base of Cutler’s right thumb (known in layman’s terms as a Bennett’s fracture), Viola inserted three screws and two pins near the bottom of the first metacarpal. The hardware eventually will be removed.
Viola’s unique fracture repair technique and the expertise of his Steadman Clinic colleagues has made the 22-year-old facility a haven for high-profile professional athletes such as Cutler hoping to minimize recovery times from serious injuries. The clinic’s client list reads like an ESPN Wide World of Sports all-star roster: New York Yankees third baseman Alex Rodriguez, New York Giants defensive end Osi Umeyiora, Buffalo Bills quarterback Jack Kemp, Denver Broncos quarterback John Elway, Minnesota Timberwolves point guard Ricky Rubio, Los Angeles Lakers shooting guard Kobe Bryant, Pittsburgh Penguins forward Mike Comrie, golfer Greg Norman, tennis greats Martina Navratilova, Billie Jean King and Lindsay Davenport, and top skiers Phil Mahre, Picabo Street and Bode Miller.
“Most physicians look at it from a ‘What should you do?’ standpoint,” Viola, a medical consultant to the U.S. Ski Team, Colorado Rockies and the Denver Broncos, told the Chicago Tribune in a rare interview late last year. “Athletes don’t look at things that way. They want to know how they can push the limit. We give them the option of fixing things with hardware, which provides support and takes away pain so often it gets them back in the game a lot faster. Some older, more classically trained orthopedists would consider it aggressive, but it’s becoming more common to fix people with plates and screws and get them back to competition as soon as possible.”
An expeditious return to competition—whether it be an athletic contest or the perpetual struggle for economic security—has influenced much of the innovation in orthopedic implants in recent years. Patient expectations, desires and needs have evolved dramatically since British surgeon Sir John Charnley devised the total hip replacement nearly 50 years ago. Since the debut of the RCH 1000 (the official name of Charnley’s ultra-high molecular weight polyethylene hip socket), patients have come to expect more from their implants. While pain relief remains the primary driver of hip and knee replacement surgery, the desire to maintain an active lifestyle or work well beyond retirement age also have become motivating factors. The possibility of life without golf, for instance, prompted 63-year-old William Mills of Philadelphia, Pa., to undergo a double knee replacement in 2006. A similar desire led retired chemist Edward Moore to replace his aging knee three years ago after pain began limiting his activity. His daughter had reservations about the procedure but Moore never gave it a second thought.
“I didn’t do much mulling about it,” he told The New York Times
in February. “It just seemed like the knee would be hampering me for the rest of my life, and that sounded like a bad idea.”
Hardly anything hampers Moore now. Having fully recovered from his knee replacement surgery, the Woodbury, N.J., resident has resumed a full slate of activities. Last September, in fact, just two days after turning 94, Moore took his wind surfer to Lakes Bay, a top-ranked windsurfing site near Atlantic City, N.J. “I got up on the board and I sailed,” he said.
The artificial joints that sustain the recreational hobbies of active nonagenarians like Moore and baby boomers like Mills (he biked 250 miles through Germany a mere six months after undergoing double knee surgery) are the by-products of more than half a century of research and development, materials testing, ingenuity, foresight, and trial and error.
Most of the early man-made hips and knees were crude devices (at least by 21st-century standards), designed specifically to serve a sedentary elderly patient population. In 1891, German professor Themistocles Glück created an ivory ball and hip socket that attached to the bone with nickel-plated screws. Several decades later, implant designers had migrated to steel or chrome, and while those joints relieved arthritis pain, they quickly wore down and easily loosened, necessitating repeat surgeries. Teflon wasn’t much better—the material triggered bone tissue degeneration (osteolysis) and wore out within two years.
Charnley’s hip design became the gold standard in artificial joint replacement due to its relatively low wear and femoral-acetabular component marriage of metal (originally stainless steel) and ultra-
high molecular weight polyethylene (UHMWPE), a biocompatible plastic with excellent impact strength, a low coefficient of friction and good fatigue resistance. Gamma irradiation of UHMWPE implants induces cross-linking and can improve wear resistance but it also can lead to chain scission and resulting oxidative degeneration, which can weaken the implant and ultimately cause its failure.
For more than two decades, the Charnley Low Friction Arthroplasty design was the world’s most-used hip replacement system, surpassing other available options like the ivory hip prosthesis developed by Burmese orthopedic surgeon San Baw, M.D., to replace ununited fractures of the femoral neck.
Though it was considered revolutionary at the time, Charnley’s Low Friction design contained a significant shortcoming—its small femoral head (22.25 millimeters) produced considerable wear debris, which was not an issue for the targeted couch potato patient but a serious problem for active folks.
That shortcoming might have been irrelevant to the evolution of implant design had future retirees remained as sedentary as their predecessors. But baby boomers—that throng of 79 million men and women who spent part of their youth marching in support of civil rights and protesting the Vietnam War—refused to sit still in their Golden Years. The boomers’ desire and determination to maintain their mobility as they approached retirement represented a radical shift from tradition but it also presented a golden opportunity to orthopedic firms that could improve both the quality and longevity of existing implants.
Such a demographic shift has resulted in a bevy of new products over the last two decades as companies developed materials and devices designed to withstand the daily vigors of an active joint.
Invibio struck gold in the late 1990s with the development of implantable polyetheretherketone (PEEK), an organic polymer thermoplastic that has become a popular alternative to UHMWPE for its strength, durability, lubricity, and X-ray translucency as well as its biocompatibility and biostability.
PEEK’s mechanical properties can be tailored to meet a company’s specific requirements. For example, the material’s strength and stiffness can be increased by adding carbon fibers to the polymer matrix, thus enabling orthopedic device manufacturers to develop applications that satisfy high-strength requirements. Invibio’s carbon fiber-reinforced (CFR) technology currently is used in the EnduRo knee revision system developed by Aesculap Inc. for patients suffering from a failed total knee arthroplasty. The system—approved by the U.S. Food and Drug Administration (FDA) in December 2010—is designed to increase implant longevity and minimize (or ideally eliminate) the need for revision knee surgery, according to Center Valley, Pa.-based Aesculap.
PEEK’s imaging properties also can be tailored by adding various concentrations of barium sulphate. The addition of this inorganic compound helps create a material that easily can be inspected post operatively through traditional imaging techniques without the generation of scatter or other imaging artifacts.
In addition to its mechanical and adaptable properties, implantable-grade PEEK can be processed through several methods, including injection molding, extrusion, compression molding, machining from plates/rods and powder coating.
PEEK, however, has its limitations. One of the major disadvantages of the material is its inability to blend well with bone, making it a difficult choice for orthopedic applications that require osteointegration.
Over the last decade, orthopedic manufacturers have experimented with ceramics and various biologics to achieve optimal bone ingrowth. Amedica Corporation, for instance, has discovered the merits of silicon nitride (Si3N4), a strong, heat-resistant material used in the automotive and aerospace industries. The Salt Lake City, Utah-based spinal and reconstructive implant maker is incorporating the material in its products due to its superior strength and imaging characteristics.
“Your standard materials for both implants and instruments is the basic stainless steel, cobalt chrome, titanium, and tantalum. And of course, ultra high molecular weight polyethylene lives with us every day,” noted Tobias Buck, chairman and CEO of Paragon Medical Inc., a Pierceton, Ind.-based Tier 1 supplier of cases, trays, surgical instruments and implantable components. “But ceramics is a material that will truly change the way implants are configured in the future and certainly the way they are configured today. You’re dealing with aluminum oxide, there’s zirconium oxide, and what that is doing is mitigating wear. You have some incredible composite materials currently in the market that seek to make the implant more stable, extend its life and better integrate with the body.”
One of those innovative composites is made by Ceramatec Inc., a Salt Lake firm focusing on the research and development of ceramic technologies. The company has designed a porous, foam-like scaffold that contains channels to allow bone ingrowth and solid struts to support weight-bearing loads. The scaffolds, according to Ceramatec, can be pre-infiltrated with hydroxyapatite, beta-tricalcium phosphate, bone morphogenetic protein, collagen and growth factors to maximize healing and osteointegration. In addition, the pore shape, size, aspect ratio, volume, channel spacing, alignment and interconnectivity easily can be controlled with the scaffold.
Another groundbreaking implant composite could be added to the market later this year by InVivo Therapeutics Holdings Corp., which is awaiting Investigational Device Exemption approval of its biocompatible polymer-based scaffolding. With the FDA’s blessing, the Cambridge, Mass.-based firm will begin testing its scaffolding in patients with acute spinal cord injuries (SCIs)—traumatic damage that results in either a bruise (also called a contusion), a partial tear, or a complete tear (a.k.a. transection) in the spinal cord. The open label clinical study is designed to evaluate the safety and efficacy of InVivo’s biopolymer scaffolding treatment in 10 SCI patients.
The scaffolding treatment, according to the company, provides structural support to a damaged spinal cord in order to prevent tissue scarring and improve both recovery and prognosis after a traumatic SCI. InVivo uses technology co-invented by Massachusetts Institute of Technology professor Robert Langer, Sc.D. (a member of the company’s scientific advisory board) and Joseph P. Vacanti, M.D., surgeon-in-chief and chief of pediatric surgery at Massachusetts General Hospital for Children in Boston.
InVivo’s scaffold device is made of polylactic-co-glycolic acid, a biodegradable, biocompatible polymer that is used in surgical sutures, drug delivery devices and tissue engineering applications. The product is designed to prevent cascading inflammation, scarring or secondary injuries commonly associated with SCIs that often lead to permanent paralysis.
The sponge-like scaffold generally is about a centimeter in length, though its size can vary depending on the SCI. Surgeons implant the scaffold directly into the injury site, guided by images taken shortly before the procedure and with ultrasound.
Beyond reducing inflammation and helping to prevent secondary injury, the scaffolding provides a matrix to promote regrowth and reorganization of neurons and neurites. The treatment also serves as a “synthetic extracellular matrix” to promote the survival of surrounding neurons, according to InVivo.
The scaffolding could be used with currently available fixation systems. It would be completely absorbed by the body within 12 weeks.
Some of the most novel implant technologies involve cutting-edge orthobiologic materials such as woven fabrics and cancellous bone. Amedica, the company using silicon nitride in its implants (the same material used in the space shuttle), also offers a product called Dynamic Bone, a customized, compressed demineralized cancellous bone that expands like a sponge upon hydration. As an osteoconductive material, Dynamic Bone is ideally suited for spinal fusion procedures, and can be hydrated with osteoinductive liquids such as bone marrow aspirate, bone morphogenetic proteins or other viable tissue matrix products. Amedica claims its Dynamic Bone product is unique in its ability to continually expand after it is placed within the vertebral body, filling any open cavity for a custom press-fit. Such a custom fit ultimately could help improve overall spinal fusion rates.
Solvay Advanced Polymers LLC has teamed up with Perkasie, Pa.-based Secant Medical LLC to produce implantable biomedical fabric structures for therapeutic devices in orthopedics, cardiovascular devices, tissue engineering, neurology and general surgery. Secant uses Zeniva PEEK resin from Solvay to produce the implants.
“We are working with [Secant] to talk to customers about how to use a fabric in a minimally invasive way and achieve different types of structural components,” said Shawn Shorrock, global healthcare market manager for Solvay Specialty Polymers, a global provider of high-performance plastics. “It’s interesting for things like ligament replacement but it’s also interesting for things like annulus repair and different kinds of shoulder repair. It’s a very unique opportunity because this folded piece of fabric that has a lot of structure to it can be inserted it into place through a catheter via a minimally invasive procedure. It expands in-situ and you can fill it with bone cement, for example, or you can put some additional component in there to give it some structure but it can also be inserted in a minimally invasive way. It really opens up the opportunities and provides a whole new way of looking at things.”
Indeed, the opportunities are boundless for innovative implant materials such as knitted fabrics and ceramic scaffolds. But there still is room for improvement—failures and limited lifespans are still a significant problem for manufacturers. Industry data suggest that roughly 17 percent of patients that receive total joint replacements undergo additional surgery due to device loosening in the body. The failure rate of metal-on-metal hips is perhaps most disturbing: A British study showed that 6.2 percent of patients with all-metal implants needed corrective surgery, usually to replace the device, within five years. It also confirmed claims that women were more likely to need revision surgeries, as are patients who received their implants around 2004, when many hips were redesigned to include a larger head, or ball, of the joint. According to researchers, the larger the joint head, the earlier the all-metal hip device failed.
Attempts to curtail these failures have spawned advancements in implant design and instrumentation over the last several decades. Patient-specific devices have become an increasingly popular way for manufacturers to compensate for shortcomings in existing designs and accommodate joint deformities in patients. Most orthopedic OEMs have developed patient-specific implants (PSI) as an alternative to their traditional models, which come in limited sizes and are based on measurements taken either from product literature or a small sampling of patient data. Standard joint replacements generally do not account for variations in mediolateral or antero-posterior dimensions, nor do they reflect the precise curvature of a bone canal in specific patient populations. The lack of such data during the design phase can impact an implant’s chances of failure within the body, experts claim.
By more closely matching the implant to the patient, manufacturers can increase a new joint’s chances of success and minimize the need for revision surgeries.
“There’s a lot more discussion lately on the implantable side with custom devices, where manufacturers try to match the implant as close as possible to the original anatomic structure of the patient,” noted Dax Strohmeyer, president of Upper Saddle River, N.J.-based Triangle Manufacturing Co. Inc., a company specializing in precision engineering and manufacturing of complex, tight-tolerance machined parts and assemblies, including hip, knee, shoulder and spinal implants.
Robotic systems have been developed in recent years to better fit hip and knee implants to patients.
The robot uses an end mill to machine the bone to fit the implant, and the tool path is generated based on a computed tomography-derived computer aided design (CAD) model of the joint and a CAD model of the implant. Studies have proven that robots can achieve a more precise cutting operation than the average orthopedic surgeon can achieve using hand tools and cutting guides. One study showed the average contact surface between the bone and the implant to be only 50 percent when using conventional methods—an insufficient level to ensure prompt and secure fixation. Robots, on the other hand, can achieve an average bone-implant contact surface of 95 percent, which reduces the fixation time and improves the initial stability of the implant. A robot is capable of performing cutting operations of complex freeform surfaces and is not limited to planar cuts, as is the case when using conventional cutting methods.
Perhaps to better compete with the robots (or to spite them), OEM implant manufacturers are designing smaller devices, components and instruments that can be used in minimally invasive surgery to replace the smaller joints of the hand, wrist, elbow and ankle. Symmetry Medical Inc. President and CEO Thomas J. Sullivan said he has noticed more demand for instruments that improve visibility and access. Based in Warsaw, Ind., Symmetry supplies implants, instruments and cases to orthopedic device manufacturers.
“We are seeing interest from our OEM customers and their surgeons for instrumentation that enables better visibility and access through smaller incisions,” Sullivan told Orthopedic Design & Technology. “We know in the past the incision was much larger than it is today. The trend toward more minimally invasive has continued with customers looking to minimize tissue disruption to speed recovery and yet still have the same great outcome. To achieve that goal, we see a need to complement the smaller incision with proper retraction for access, instruments that are sized and ergonomic to enable you to move effectively within the joint cavity, and of course visibility for exposure and alignment. Without all three, simply a smaller incision might be to the sacrifice of the historically excellent long term clinical outcome.”
The demand for smaller, more complex shapes and components has forced many companies to become adept at micromolding. Spectrum Plastics Group executives are investigating the viability of providing “one-off” services to customers (the ability to make just one copy of something). Such a service, however, could be costly, said Mark D. Schaefer, corporate vice president of business development for the Minneapolis, Minn.-based provider of rapid prototyping, additive manufacturing, quick-turn tooling and molding, injection molding of thermoplastic and liquid silicone rubber, and contract manufacturing services.
“If we were to build an injection mold and make one part, the lead time, even with our FastTrack tool building capability, would be too long and cost per part would be astronomical,” Schaefer explained. “However, with additive manufacturing processes and a CAD file you can make one piece out of PEEK. It is a technology that we are investigating because we also do laser sintering of nylon.
However, this would be a major capital investment requiring totally new equipment to do it in PEEK. The market is in its infancy.”
The challenge posed by smaller orthopedic implants and components is easily conquerable compared with the more complex mix of increasingly stringent regulatory requirements and pricing pressure. Contract manufacturers, suppliers and OEMs are under perpetual pressure to reduce costs to compensate for shrinking reimbursement rates and increased competition from a globalized market.
Over the next four years, the United States is expected to add millions of people to the Medicare-eligible pool, a population that often seeks orthopedic care. However, Medicare reimbursements for treatment seldom covers the cost of care, which gives surgeons few options other than restricting access to elderly patients or absorbing a loss on services provided.
Compounding these pressures are more rigorous FDA requirements for quality assurance and basic tasks, including documentation and inspection reporting, process validation and compliance with ISO 13485 standards, industry experts said.
“FDA regulations placed on our customers continue to raise the bar to manufacture orthopedic implants,” noted Sarah Stanley, business development manager for Tegra Medical, a contract manufacturer and assembly services provider based in Franklin, Mass. “We are experiencing more rigorous requirements with equipment validations, special process validations, capability analysis, risk analysis, control plans and measurement systems analysis. We are hearing from customers that the FDA could soon require implants to be laser marked with a serialized lot number. We have a few customers that have already changed their requirements to include serialized lot numbers on all implants that we manufacture.”
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For more than a century, orthopedic implant manufacturers and design engineers have tried their best to create the perfect implant. They’ve experimented with various materials—ivory, metal, titanium, tantalum, ceramic, glass, even plaster of paris—and designs only to discover that perfection exists only in nature. Attempts to achieve the near impossible (and more importantly, prevent implant failure) nevertheless have continued with the development of patient-specific devices and joint replacement components that are smaller, more complex and can be inserted through minimally invasive procedures. As the industry marks a half century since the debut of the “modern” hip implant, research continues into innovative substances that might one day lead to everlasting man-made joints. For such a breakthrough to occur, though, experts claim the industry must resolve the paradox created by increasing regulatory requirements and the enormous pressure to reduce manufacturing costs. As Paragon Medical’s Buck observed: “There’s an interesting paradox that exists in this industry. How can you have the amplification of regulatory requirements across the board—which are very restrictive and
amplify costs—in the face of extreme downward price pressure? How can those two things co-exist? The pendulum has to swing back to the middle on the application of regulatory doctrine so there is a greater level of sanity in the manufacturing space.” That may prove to be more elusive than the perfect implant.