Intelligent Implants
The merging of microprocessors and mobile technology is ushering in the next generation of “smart” orthopedic devices.
The night was cool and comfortable, at least by midsummer standards. Some residents of the Wyoming Hill section of Melrose, Mass., slept with their windows open that evening, happy to finally breathe in air that was not recycled and artificially cooled. Those with open windows were the ones that first smelled the smoke and heard the approach of fire engines. The first fire truck in a caravan of pumpers, rescue vehicles and emergency personnel arrived at the burning, three-story home at 10 Everett St. shortly after 2 a.m. on Aug. 7, 2005. Within minutes, the quiet, tree-lined street hosted a brazen display of revolving red and blue lights and a discordant symphony of ear-splitting sirens that shattered the tranquility of the working-class neighborhood.
Neil F. Sullivan Jr. was among the first dozen or so firefighters dispatched to the three-alarm blaze. The son of a retired Boston, Mass., firefighter and the eldest of four brothers, Sullivan had been with his hometown fire department for six years. He loved his job. Fellow firefighters described him as a “tireless worker,” and a “good, all-American kid” who also painted houses and tended bar at a VFW post to support his wife and infant son. Not long before that fateful night, Sullivan moved his family into a new home. He wanted his children to grow up in Melrose, a Boston suburb located in the heart of a triangle created by Interstates 93, 95 and U.S. Route 1. The 4.8-square-mile city reportedly was named after a small, rugged town in central Scotland near King Arthur’s burial site in the Eildon Hills.
Neighbors of the burning Everett Street Victorian noticed smoke pouring from the back of the house and called 911 shortly before 2 a.m. Within minutes, firefighters arrived on scene and called in a second alarm. Sullivan, along with firefighter Scott Alley and Lt. Mike Sullivan, began searching the house for occupants. Another firefighter, Mike Cole, set up an aerial ladder.
As the homeowner and her family left the house, a relief valve on a propane tank for their grill let go, creating a brief fireball (the tank itself, however, did not explode). As another engine and ladder truck raced to the scene, firefighters advanced attack lines to the first and second floors to extinguish the blaze. At that point, mutual aid companies had begun to arrive. News accounts of the incident claim that nine fire companies from seven different cities helped Melrose firefighters battle the blaze that morning.
Homeowner Lisa Bouchard watched the scene unfold almost trancelike from a safe distance across the street. Standing with her husband, son and new puppy, Bouchard glanced toward the second floor of her house, thinking “there was going to be that pivotal moment when the walls start collapsing,” she told The Melrose Free Press. Then she heard four words that sent chills up her spine: “There’s a man down.”
That man was Neil Sullivan. He was lying on the sidewalk, with blood seeping through the right pants leg of his heavy firefighting gear. Somehow, his right leg had become pinned between the ladder truck and Engine 2; Bouchard and other witnesses saw two men frenetically push the ladder truck to free Sullivan. An uncomfortable silence followed. Bouchard later told the Free Press that it “seemed like forever” before Sullivan was stabilized, put on a stretcher and loaded into a waiting ambulance.
If the next four days were a blur to his family, they were even worse for Sullivan. He doesn’t remember them at all. He doesn’t remember arriving in the emergency room. He can’t recall the 23 blood transfusions he received to replenish his depleted supply. And he has no recollection of his wife Jessica sitting dutifully by his hospital bed, waiting for him to regain consciousness.
Sullivan’s memory of the accident is almost as bad. To this day, his mind, either for the purpose of self-preservation or perhaps due to disassociation, only will relinquish certain memories of the night of the fire, like a string of blurry photographs in a psychedelic slide show. Sullivan can recall the basics without trouble—things such as the time, date, location, the firefighters on scene with him and the search for occupants of the burning house—but a clear picture of the events leading up to his life-altering injury remain elusive. Sullivan underwent emergency surgery after the accident, but doctors were unable to save his right leg. They amputated it above the knee.
Suddenly, the man who liked to help others in need now needed help himself. But Sullivan never actively sought help to deal with his new condition, nor did he wallow in self-pity about it. Upon waking to news of his loss, the former firefighter had only one thought—getting his life back.
“Laying in that hospital bed, all I could think about was ‘I have a young family. I’m a relatively young guy.’ I just wanted to get my life back,” he said. “I wanted to get up and get moving again. After meeting with other amputees that came to visit me … my main focus was to get on with things like raising a family, playing ball in the yard, driving a car and getting my independence back.”
Sullivan didn’t have much trouble reclaiming his independence. Like most amputees, he was fitted with a prosthetic leg that enabled him to walk again and perform some of the tasks most people take for granted—driving a car, for instance, swinging a golf club or, simply standing in an upright position. Perhaps most importantly, though, Sullivan’s artificial limb allowed him to raise a family (he has four children; the youngest was born over the summer) and revel in the joy of such simple pleasures as playing ball with his son.
Those kinds of small victories should have given Sullivan a sense of accomplishment. He did, after all, achieve most of the goals he set for himself in those first few weeks after the accident. But there were things Sullivan still could not do very well even with his high-tech artificial leg—things as simple as climbing stairs, walking backwards or navigating rocky terrain.
“As an amputee, you’re always hoping to restore normalcy as much as you can,” noted Jason Lalla, an above-the-knee amputee and an American Board for Certification in Orthotics and Prosthetics-certified prosthetist for Next Step Orthotics & Prosthetics Inc., a privately held orthotics and prosthetics provider headquartered in Manchester, N.H., with offices in Newton, Mass., and Warwick, R.I.“When a person without an amputation walks around, changes speed, changes direction and changes terrain, he really is not thinking about those things. Most healthy people are not thinking about what muscles they need to fire to walk faster or what they need to do to be able to stand without the worry of falling or what they need to do to descend a hill. If you have an amputation, there are more things you have to think about. That can become taxing on your mind and taxing on your body and nobody wants that.”
The desire for normal subconscious mobility among amputees has driven companies such as Otto Bock HealthCare, Bulow BioTech Prosthetics of Nashville, Tenn., and Össur of Reykjavik, Iceland, to develop “smart” prostheses that use artificial intelligence (AI) and microprocessors to function as an integrated extension of its users. Power motion technology has helped lift amputees to a higher level of mobility; from the subtle elevation of the toe during swing phase to the powerful knee extension needed for foot-over-foot stair climbing, power motion allows amputees to move around without first having to think about it.
Prosthetic limbs with computers and sensors have existed for about two decades, though they’ve been around much longer in the pages of science fiction. Only recently, however, have researchers developed a technology that thinks for an amputee.
The Genium Bionic Prosthetic System from Duderstadt, Germany-based Otto Bock Healthcare contains six sensors, an accelerometer, a gyroscope and a microprocessor that takes multiple readings per second to adjust the knee as the amputee moves. Similar to the technology used in interactive video games, the microprocessor “reads” the location of the foot and ground to dictate the next anticipated motion.
“Because it can read the foot, the position of the foot and how fast it’s coming out, the microprocessor, through the sensors, tells the knee what to do,” explained Next Step Orthotics & Prosthetics President Matthew Albuquerque. “The microprocessor makes small changes to the hydraulic unit while somebody is walking. The microprocessor has sensors in the prosthesis that reads where the foot is. If the microprocessor reads that the foot is on the ground it doesn’t let the knee bend because obviously you don’t want your knee bent if you’re standing on it. Conversely, as your weight comes off of your foot, the microprocessor reads that and tells the knee to release.”
The Genium’s battery enables the device to stay charged for five days, and a Bluetooth remote allows the user to program the leg for a variety of activities such as skiing, skating, biking and snowboarding.
Össur’s newest prosthesis, the Power Knee, works in a similar way, employing AI systems, motion sensors and wireless communication capabilities to help the knee “learn” its amputee’s walking style and automatically make real-time adjustments based on changes in speed, stride or terrain.
Striking the Right Balance in TJA
Orthopedic surgeons are not perfect. They rely largely on their training, experience, and the “feel” of an implant to properly place it in the body. Experts believe such an imperfect navigation method has played a significant role in the rising number of implant failures and revision surgeries in recent years, though part of the increase also can be attributed to factors such as infection, loosening, and overall wear.
Demand for both revision surgery and total hip and knee replacement procedures is expected to grow over the next two decades as aging baby boomers attempt to delay the inevitable and stay physically active well into their 70s and 80s. A Journal of Bone & Joint Surgery study estimates a 174 percent increase in demand for primary total hip arthroplasty by 2030, and a staggering 673 percent jump in desire for total knee arthroplasty. The number of correction procedures is expected to crest even sooner, with hip revisions doubling by 2026 and knee revisions doubling by 2015.
Despite such demand, revision surgery and total joint replacements are risky medical procedures. Revisions are particularly difficult due to the reduced amount of bone that exists to place the new implant; as a result, revisions generally carry a higher complication rate than replacement procedures.
Total joint arthroplasty can be complicated as well, but for different reasons. One of the main challenges with this procedure in the knee is the lack of a reliable system to ensure optimal tissue balance. Practically since the first knee replacement was performed in the 1960s, surgeons have relied on little more than their skills, experience and keen sense of touch to balance soft tissue and properly align both the implant and limb axis. Some experts believe total joint arthroplasty is more of an art than a science.
Jay Pierce is hoping to inject more science into the procedure. His company, OrthoSensor Inc., has developed an “intelligent” disposable insert that provides evidence of proper soft tissue balance during kneereplacements. OrthoSensor’s Knee Trial uses embedded sensors that can detect pressure or load data on various compartments of the knee and wirelessly transmit the data to a graphic user interface (which can be shown on any standard computer or tablet, according to Pierce, the company’s CEO). The insert—cleared by the U.S. Food and Drug Administration in late 2009—is designed to replace the standard spacer block typically used to balance the knee during a replacement procedure.
Providing orthopedic surgeons with pressure and load data gives them a fail-safe way of determining whether one compartment of the knee has more pressure than the other, a condition that can lead to premature wear as well as pain and joint instability. To correct an imbalance using OrthoSensor’s Knee Trial, surgeons first have to realign the implant, releasing tight ligaments to equalize the pressure and optimize soft tissue balance through a full range of motion. Once that balance is reached, the OrthoSensor Knee Trial can be disposed of and replaced with the final implant.
“For the first time, we can provide surgeons with evidence that the knee is balanced before it is closed up,” Pierce told Orthopedic Design & Technology.
OrthoSensor has partnered with Stryker Corp. on the Knee Trial, offering the device for commercial use with the Kalamazoo, Mich.-based implant firm’s Triathlon Knee System.
With a platform technology that integrates microelectronics, sensing technology and radiofrequency telemetry, OrthoSensor developed its Trial expertise initially for unicompartmental, biocompartmental and total knee replacements. But the technology can be applied to other parts of the body as well, including the hip, spine and shoulder. Pierce said the company has negotiated an agreement with a spine implant company, and is working to launch a clinical trial in 2012.
Eventually, Pierce hopes to produce a line of intelligent implants that would enable clinicians to remotely monitor various parameters specific to the implant and the surrounding bone, such as relative loading and position, material wear, osteolysis, motion, heat and interface changes. The Sunrise, Fla.-based company currently is working to develop a sensor similar to the kind found in its disposable surgical tools that can be embedded into hip, knee or spine implants. Pierce said these sensors eventually could be used to alert doctors to the early signs of an infection, bone density changes, or the slightest loosening of an implant.
“Implants used to be all about mechanics, geometric design and material science, but the future of orthopedics is going to be based on the integration of electronics, wireless telemetry and microsensors that can provide physicians with the data they need to improve patient care,” he noted.
Pursuing the Revision-Free Implant
Earlier this year, biomaterials researcher Paul Wooley posed an interesting question to a group of orthopedic industry professionals. Is it possible, he asked the group, to achieve a revision-free implant?
Such a concept, of course, would be frowned upon by OEMs, which currently design hip and knee implants to last about 15 years. There are exceptions, though:
Legion Knee from Smith & Nephew plc, an implant made from a lightweight, hypoallergenic metal called Oxynium and a highly cross-linked plastic, reportedly can last 30 years; the Taperloc Hip System developed by Warsaw, Ind.-based Biomet Inc. can survive up to 26 years before loosening; and the NextGen knee from Zimmer Holdings Inc. has an average lifespan of more than 20 years, according to the company.
Regardless of their reputed lifespans, hip and knee implants can fail in as little as two years due to inadequate surgical techniques, infection, and patient noncompliance. More often than not, however, the device’s material is to blame: Both metal-on-metal and metal-on-polyethylene hips, for instance, generate wear debris, which can cause inflammation, bone damage and loosening. Ceramic hips have a high wear resistance but they tend to squeak and are more susceptible to fractures.
Wooley believes these problems easily can be avoided by using composite materials that allow design engineers to create honeycomb structures that better promote bone ingrowth, or osseointegration. Finding composite materials can be tricky, though—they often are found outside of the medical industry.
The National Institute for Aviation Research at Wichita State University and Via Christi Research, for example, currently are exploring the use of carbon foam used in aircraft wings to make hip joints, battlefield splints and hospital gurneys. Wooley claims the composite material—fiber laid down in a matrix that is then embedded in a plastic or other resin to produce a strong, spongy substance—mimics the structure of bone.
Composite materials, however, are not the only route to better osseointegration. New technologies such as chemical etching, fast ceramic production, protein nanoclusters and electron beam melting are providing implant manufacturers with alternative ways of producing better quality devices.
The electron beam melting technology (EBM) developed by Arcam AB of Gothenburg, Sweden, creates medical components by melting thin layers of metal powder with an electron beam. The process takes place in a vacuum chamber, giving the material a very high purity content. The vacuum-high power energy source also makes the material considerably stronger than substances produced by more conventional methods. Implants produced with EBM feature a chemical composition within stipulated standards, fully dense material with fine microstructure, high ductility and good fatigue characteristics, according to Arcam. The additive, layer-based nature of the process also makes it possible to manufacture implants with trabecular structures that enhanceosseointegration and use less material.
“Instead of using traditional methods where you start with something and cut away what you don’t want to have, in additive manufacturing we start with a powder and fuse it together to create what we want to have,” noted Magnus Rene, Arcam’s CEO. “In orthopedics that gives us the geometric freedom to build parts that combine solids and porous materials which integrate trabecular structures directly into the part.Additive manufacturing gives us the ability to make parts that have complex trabecular structures made for bone ingrowth.”
The ‘Silent Hip’ and Osteobiologic Containment Bag
Mother Nature does not like to be fooled. But man, for various reasons, has tried his best to trick her, hoping eventually to learn her most coveted design secrets. The only lesson man has learned though, is that Mother Nature does not easily reveal her secrets (no surprise there). Undaunted by past failures, man continues his quest to mimic Mother Nature’s designs. Perhaps nowhere is this mission more apparent than in the orthopedic industry, where researchers have spent decades experimenting with materials, technology and pharmaceuticals to repair broken body parts, from torn cartilage and brittle bones to dehydrated spinal discs and worn hips.
Bones and joints are two of the most difficult body parts to imitate due to their biological compositions. Man most definitely has mastered the art of artificial ball-and-socket creation, conjuring hips and knees composed of a mix of stainless steel, cobalt chrome, titanium, ceramic and polyethylene. None of those combinations though, are as good as the original. Like the bona fide design, man-made artificial joints wear out over time, only sooner than Mother Nature’s.
Orthopedic manufacturers are trying to conquer that design flaw by introducing materials that reduce wear and prevent osteolysis (bone death). Biomet, for instance, has developed polyethylene acetabular liners and tibial bearings that contain Vitamin E, a natural oxidant and proven protectant against oxidation.
“E1 polyethylene with large femoral heads enables surgeons to give patients a replacement hip that feels almost like what they originally had,” said Lance Perry, vice president and general manager, Global Knees, for Biomet. “The whole concept of the ‘silent hip’ continues to be an achievable goal—the hip [replacement] that a surgeon performs and then the patient forgets about. I think there is going to be a wave in the total knee replacement world for something similar but we’re not there yet. Companies are taking a conservative approach today and building on technologies that have worked in the past instead of trying to do something revolutionary.”
Indeed, the revolutionary inventions are taking place in the orthobiologics realm, where companies such as Secant Medical LLC are doing their best to copy Mother Nature through bioresorbable designsSecant, meanwhile, is leveraging its expertise in woven biomedical textiles to create new applications in minimally invasive surgery, sports medicine, spine stabilization rotator cuff repair. The Perkasie, Pa.-based developer and manufacturer of biomedical textile components also has started to branch out into the bioresorbable material world, as companies increasingly attempt to use Mother Nature as a model and mentor in developing new orthopedic products.
“We had a particular application where a client had an allograft bone materialthat needed containment,” recalled Jeff Koslosky, vice president of Secant Medical’s Advanced Technologies Group. “This involved osteobiologics—biomaterials that are put inside the body and are designed to grow orthopedic tissue. [This company] wanted to localize the allograft at a particular site for a period of time, within a containment bag—but they wanted the bag we created for them to degrade over time.
We worked collaboratively with this [company’s] team to derive a textile structure that would function like a bag which would contain the allograft material. The bag was constructed from a bioresorbable polymer that in about three to six months would break down in the body and resorb. The resulting device would leave behind only the patient’s bone tissue that had been re-generated with this osteobiologic material, so if you looked at the patient a year down the road, there would be no evidence that a textile structure was once in place.”
The technological revolutions taking place in orthopedics, however, are not limited to the complexities of osseointegration, biocompatibility or implant longevity. Even instrument cases and tray graphics are undergoing radical transformations. Medicraft Inc., a division of PPM in Elmwood Park, N.J., unveiled DCG (digital contact graphics) in late-2009, a process that embeds high-resolution, multi-color graphics on metal in a single step. The graphics are highly scratch-resistant and provide a high-definition appearance compared with traditional graphics. The process is more cost-efficient than traditional silkscreening and helps prolong the use of cases and trays, according to company executives.
“Case and tray graphics have a function. It’s part of the packaging, and packaging is what helps sell the product,” said Michael Phillips, president of operations for Phillips Precision Medicraft Delivery Systems division.“The product has to look good, be cost effective and have high quality. Most companies would like people to walk past an operating room and be able to immediately recognize their product just by looking at it. Branding is very important. DCG will allow that to happen. High-definition imaging is far nicer than silkscreening.”
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It was only a matter of time before the medical device industry integrated computers and mobile technology to improve upon its implantable devices. Sensors and microprocessors are creating a new class of next-generation prosthetics and implants— products that not only think for the patient, but have the potential to prevent and one day solve the compatibility and biological integration issues that have vexed design engineers for decades. Of course, computers will never hold a candle to Mother Nature’s original work. As Secant’s Koslosky told ODT, “The closer we can get to a natural biologic repair, the better. Helping the body heal itself is an area where truly forward-looking technologies will continue to occur. Biologics is the future.”