|
|
July 15, 2000 | |||
|
|||||
|
|
|
|
|
|
|
Articles
|
 |
Prosthetic Knees—New Directions
Shorter reminisced about the moment when he saw the original device demonstrated by Nabco, a division of Kobe Steel, at the ISPO World Congress in Kobe, Japan, in 1989. Recognizing its value in prosthetic applications, Shorter negotiated a license to use the technology—not just to market, but to use and improve on the design. The papers were signed in 1990, and by 1995 Blatchford had improved the design, replacing the original wired batteries with an improved battery pack—and supplying about 1,000 units that first year of production. The unit applies its ‘intelligence’ to swing control, not stance, said Shorter. “It uses a proximity switch to sense the rate of piston movement (swing) and adjust it, applying appropriate resistance (through valves) to decelerate as it comes to full extension.” Although there are five settings of resistance, adjustments may fall between settings, allowing further variation. In order to outfit a patient with an IP, the prosthetist must determine from the patient how fast he/she normally walks, how fast he/she runs to catch a bus, and how slow he/she strolls at the end of a hard day—on the way to the kitchen for a glass of water, for example. The real value of the IP lies in its ability to reduce energy expenditure, Shorter said. Since the unit automatically adjusts for the wearer’s changes in pace throughout their daily routine, walking becomes automatic and requires less conscious involvement from the patient to successfully ambulate. Since 1995, Shorter added, improvements to the IP have included smaller, lighter lithium batteries. The speed of adjustment of the valve settings was also increased. He said that currently the IP only controls the swing phase—the next step in development is a natural: “We want one that intelligently controls stance, too.” Their new Adaptive Knee with stumble control has already appeared, and the first ten units are to be issued this year. “We’re on the verge of the Electronic Age,” Shorter said. “This is a very sophisticated end of the market.” But, looking to the future, he expresses concern that the less-active customers might not be considered for these products. “These units aren’t necessarily for the young and active. These should be for the majority of users—for everyday life,” he said. “It’s very challenging at the lower end of the market for minimal ambulators. They don’t need an IP. They need something ultra lightweight and safe. I’ve done a lot of work on the Atlas System—for third world countries. Through aid agencies, patients should be able to buy it for $200 to $300. Official trials are in progress now in El Salvador and Cambodia, and 3,000 are out in Africa, Russia, South America, and other developing regions. “It’s good to make progress at the top end,” Shorter concluded, “but how much good is it if the technology can’t be afforded in places where there is deliberate carnage? It’s just as important to service amputees there.” The Nylon Knee, developed by Alan Aulie in conjunction with the Veteran’s Administration and Ernest Burgess, M.D., of Prosthetic Research Study, Seattle, 1986-1989, is currently marketed by Aulie Devices Inc., of Redmond, Oregon. Described by others in the industry as “simple, durable, low-cost, functional, resistant to water, and very clever,” the Nylon Knee is designed for low maintenance and durability, said Aulie, who holds patents on the design. The Nylon Knee weighs just l.2 pounds and is by far the lightest hydraulic knee available, Aulie claimed. It was designed primarily for those amputees who wish to enjoy water sports wearing their prosthesis. Many of the original, molded, and current versions of the knee have found their way to Vietnam as charitable donations via the Prosthetics Outreach Foundation founded by Dr. Burgess, Aulie noted. The Aulie Nylon Knee affords 160 degrees flexion, which allows a wide range of everyday activities, including kneeling. The patented hydraulic control is adjustable and lightweight, with an adjustment ring that controls fluid flow by deforming the walls of the cylinder. Swing phase friction is easily adjustable, wear-compensating friction that supplements the hydraulic control, Aulie claimed, and the extension assist is intrinsic to the flexible structure of the knee—with no parts. Due to the polycentric characteristics of the structure, the Nylon Knee has moderate full-extension stability. Aulie, a mechanical engineer, noted that water is a legitimate lubricant for the Nylon Knee’s bearing system. About 500 units are currently in use, and Aulie’s new design, the Nylon Knee II, is being introduced to the marketplace currently. The new water knee is for high activity users who weigh up to 250 pounds and features a more conventional mechanism with hydraulics designed to control the longer shanks and heavier feet of large amputees. Government Participation
According to “SandiaLabNews,” Sandia’s on-line newsletter, technologies for the foot and the knee are being jointly developed by two nuclear weapons laboratories on opposite sides during the Cold War: Sandia and the Russian laboratory known as Chelyabinsk 70. Ohio Willow Wood has defined requirements for parts and will perform final lab and clinical testing, the newsletter claimed, while the Russians are creating a titanium housing. Sandia robotics researchers Mark Vaughn and Dave Kozlowski are working with Ohio Willow Wood on designing the knee’s internal workings and electronics. Although working separately on a mechanical version of the stumble-avoidance knee (see below), Mark Pitkin also has offered to advise and collaborate with efforts toward the electronic version, according to Morton Lieberman, Ph.D., retired from but currently serving Sandia on a consulting basis. Ohio Willow Wood’s Marc Taylor, research engineer, described three different knees already available from his company: The basic stabilized knee once referred to as a “safety knee” is for low activity (levels 1 and 2) patients; the pendulum knee—a 4-bar knee with air cylinder to control acceleration and deceleration—is suitable for level 2-3 patients. The newest offering from Ohio Willow Wood, the Geo-Flex™ Knee, offers a far different design than anything on the market today, as indicated by Taylor. Taylor noted that the Geo-Flex operates on the slider-crank principle and is very stable, allowing automatic recovery to full standing from 0-20 degrees knee flexion—rescuing the wearer from falls as a result of stumbles and stubbed toes. Mark Ford, marketing manager for Ohio Willow Wood, is equally proud of his company’s progress. “We’re one of the top companies in the prosthetic industry in the world,” he said. “We’ve been leading the way with new developments within the last three to five years and will continue developing our leadership in the future. Our goal is to deliver a new level of freedom and security for amputees.” Taylor is enthusiastic about their participation with Sandia in last October’s successfully created Free-Flow Foot and derives great personal satisfaction from the realization that amputees around the world will benefit as a result of their success. He is, however, reticent to discuss the current cooperative effort with Sandia on the advanced electronic knee project. “This is understandable,” said Lieberman, supporting him. “Naturally, Ohio Willow Wood wouldn’t wish to talk about design specifics for a project still in the relatively early stages. We at Sandia are currently trying to create an advanced mechanism with Ohio Willow Wood, while the Russians are working on an improved housing for the knee. Their expertise in metals and better supply of metals are invaluable to the project.” Lieberman further noted that ISTC’s (International Science & Technology Center) funding by the U.S. Department of State and the European Union for the last two years has allowed the Russians to choose the portions of the project they feel they can contribute to the most. The partnership effort required multiple letters of proposal and partnering from the United States, which Lieberman gathered from a diverse group of program supporters who appreciated the value of a program that encourages direct communication and peaceful cooperation with the Russians. The project draws upon Sandia’s electronic expertise to create the “brains” of the knee and relies on Russian materials knowledge to create the shape of the knee. Ohio Willow Wood’s expertise in production design, mechanical and clinical testing, and marketing allow the products to reach the market. “The work is a good fit with the capabilities of all involved,” said Lieberman. “It involves stress analysis, mechanical testing, reliability testing, microprocessor control, and materials analysis. It certainly helps the prosthetics industry, with its relatively small technical support, to have the resources of a giant of nuclear technology and testing available to serve the needs of amputee patients.” Rolling Joint Knee
Pitkin’s new company, Poly-Orth International, was awarded a phase of a grant titled “Rolling Joint Prosthetic Leg.” “The study is to extend the Rolling Joint technology utilized in the Free-Flow Foot and Ankle3 (released in October 1999 by Ohio Willow Wood) to a new prosthetic knee unit. That design,” he said, “will incorporate an artificial ligament currently being developed by C-70 (Nuclear Center in Russia) as part of another foot-ankle project. “The ligament’s stress-strain characteristics when tensile loads are applied is very close to that of a natural ligament,” Pitkin said. The new knee provides stance flexion up to 15 degrees during gait with the concave pattern in the moment of resistance seen in the anatomical knee as well as in the ankle.4 That means greater compliance at the beginning of stance flexion and a rapid increase of resistance when close to the knee locking position. Another feature of Pitkin’s Rolling Joint Knee is stumble-avoidance, provided by its rolling weight-activated locking system, he reported. Pitkin explained that in addition to the stance phase flexion up to 15 degrees, a prosthetic knee should mimic one more feature of an anatomical prototype. When load is abruptly applied during swing phase to a natural knee, it shouldn’t collapse; it should bear weight, even when slightly flexed. “The knee should know when it’s allowed to be bent, and make no mistakes when load is applied,” said Pitkin. “If the knee is bent at 40 degrees, what happens if the toe faces an obstacle like an unseen curb? A natural knee fixes itself, load is placed to maintain the balance of the body, and bending does not continue further. If this ability doesn’t exist in a prosthesis, the person using it places his weight on a still-bending knee which collapses.” NIH’s National Center for Medical Rehabilitation and Research identified this problem several years ago when Louis Quatrano, Ph.D., called the meeting at Sandia Lab to address the situation in conjunction with the Russian experts in what was then weapons technology. “Various key elements of a prosthetic leg were identified by the experts in the field—knee, foot, socket design, and adjustment—and the needs prioritized,” Pitkin remembered. “The Rolling Joint Knee was funded just one year ago.” Phase I of his knee study has been completed, Pitkin said, and the prototype developed by International Specialty Machinery, Kalamazoo, Michigan, was tested on four amputees at New England Sinai Hospital and Rehabilitation Center in Stoughton, Massachusetts. Prosthetic services were provided by United Prosthetics Inc., Boston, Massachusetts. Gait/motion analysis was conducted at Sinai Center for Human Performance using the four-camera Peak-Motus Motion Analysis System, Peak Technologies Inc., Englewood, Colorado, and one Kistler Force Plate, which allowed for calculation of the movements in anatomical and prosthetic joints during gait. “This confirmed that the moment of resistance in the Rolling Knee was closer to the pattern seen in a sound knee joint, compared to the prostheses owned by the subjects,” Pitkin reported with satisfaction. Prosthesis performance outcomes were measured in terms of pressure applied at the stump during gait, Pitkin said, using the Tekscan Pressure Distribution Measurement System, Tekscan Inc., Boston. Findings demonstrated that pressure and forces on the stump were decreased when the patient was wearing the Rolling Knee. “Other companies have also produced knees that allow for range of motion up to 15 degrees during weight bearing at stance phase,” Pitkin pointed out. “This is no longer unique. However, the same range of motion could be executed with different resistance of a knee unit to angulation (moment of resistance), depending on the design. A pattern of that resistance is directly associated with the forces between socket and stump at weight bearing. Greater forces are responsible for greater pain and fatigue. Therefore, to control pain, one has to control the moment of resistance in the prosthesis. It was a combination of the stance-flexion range of motion and the anatomical pattern at the moment of resistance which resulted in the reduction of forces and pressures on the amputee stump.” The Rolling Knee’s other special capabilities lie in its performance during the swing phase, where the angulation, angular velocity, and angular acceleration are the functions of the knee performance at the preceding stance phase. This ability, Pitkin suggested, will hopefully be demonstrated by the next generation of the Rolling Knee.
He avoids making specific comparisons of the Rolling Knee with existing prosthetic knees on the market. “As an engineer,” said Pitkin, “I look at the moment of resistance, the pressure on the stump and findings which are expressed in terms of research measurements.” Evidence of the capability of Rolling Joint technology was demonstrated last December when the St. Petersburg Elks, an ice hockey team Pitkin initiated in St. Petersburg, Russia (his native city), arrived in Boston (also through Pitkin’s efforts)—where they met and played a U.S. team of postal servicemen in an amazing game. Each player on the Russian team was equipped with the Rolling Joint (Free-Flow) prosthetic foot and ankle. (O & P Business News, March 15, 2000, page 49.) A similar match between the St. Petersburg Elks and a newly-organized U.S. Hockey-on-Prostheses National Team took place May 10 in Russia during the Ice Hockey World Championship. From Pitkin’s point of view, everybody won.
|
|||||||||||
| Subscribe
Submit
Classifieds Submit
Calendar Listings
Submit Letters Submit New Products Submit Articles |
