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A recent U.S. prosthetic practice survey revealed that upper-limb prosthetics represent only 5 percent of work performed by prosthetists nationwide. One might conclude from this that research efforts and dollars will be spent in similar proportion, and arm amputees might well be concerned that their needs could be overlooked in favor of the needs of larger groups such as leg amputees. Conversely, this is a very exciting period for arm amputees in search of a better prosthesis. Technologies developed for the electronics and communications industries such as batteries, miniature electronics, and microcomputers are paving the way for many new devices for adults and children. And, new materials, such as composite plastics, silicones, etc., are making lighter-weight components and more natural-looking cosmesis a reality. Media attention is drawn to "high-tech" devices like myoelectric arms, but progress also continues in body-powered devices. Some significant new products have been introduced recently and in the future we will likely see more advancement in these devices, offering the added benefits of lower cost and simplicity. Let's take a look at some of these new technologies for consumers. New electronic components The trend is very clear in new electric hands -the microprocessor is here to stay! The latest controllers for electric hands from Motion Control, Otto Bock, and Liberating Technologies, Inc. (LTI), all use small microcomputers, and they have more automatic functions than ever before. Smaller than ever, they now consume less power - a big plus for the electric-arm wearer. Proportional control is now accepted as the preferred method for myoelectric hands, because of the improved precision it affords the electric-hand wearer. "Proportional" means that the hand power is in proportion to the size of the muscle contraction. All the new microprocessor controllers provide proportional control. Formerly requiring a sacrifice in component space, the new microcomputers simply The new ProControl 2 from Motion Control -a microcomputer for electric hand and wrist control. The patented AutoCal® feature automatically adjusts to the strength of the wearer's signals during the first few seconds after it is turned on. When muscles get tired at the end of the day, the wearer can adjust for the change in muscle strength. The same control is now possible with a single muscle, or even a "pull" sensor in the harness. (Photo courtesy of Motion Control, Inc.) Hands and hooks - "terminal devices" in prosthetics vernacular - have also evolved greatly. New hands are being developed to fill several different market niches. The latest electric hand, the Motion Control Hand, promises quicker opening and closing, stronger fingers to resist bending, and a unique safety release switch that allows wearers to free themselves in an emergency if their hand "locks up." Soon, versions of the Motion Control Hand with a shorter frame will combine the stronger, quicker operation with smaller size and lighter weight. Traditional body-powered component manufacturer, Hosmer Dorrance, now offers the "Soft Voluntary Opening Hand," which is lightweight while still offering a secure grip when fully closed due to a novel cam-type mechanism. To complement their "meat-and-potatoes" line of sturdy, cable-operated arm components, Hosmer will soon offer a "Four-function Wrist" especially for bilateral amputees, which will offer spring-assisted wrist rotation, combined with wrist flexion - all controlled by the pull from the same cable that opens the hook.
The lighter hand, however, provides far less pinch force. Work-type devices like the Otto Bock Greifer and Hosmer Synergetic Prehensor can be interchanged with the artificial hand for rugged environments or where the tool-like gripping shapes better suit the task. Children's electric hands have proliferated widely, and are commonly used in most clinics, although the body-powered hooks will always be useful for kids' rugged activities. The Flexi-Wrist, by LTI, allows a hand to bend at the wrist, which is useful when grasping a tricycle handle bar or in other play activities. In combination with the electric terminal devices, electric wrist rotation is now used much more commonly and effectively with the new controllers allowing easy control of both hand and wrist. The Utah ProControl introduced co-contraction switching, which allows the wearer to turn on the electric wrist with a quick "snap" of the two control muscles. Co-contraction requires some training for the new wearer, but has proven to be the most convenient method for wrist control and is now more widely used even in other systems. The benefit to the wearer is the freedom to reposition the hand without the trouble of reaching over with the sound hand (for unilateral amputees) or awkward knee manipulation (by bilateral amputees). The result is a much more "natural" movement for the wearer. Progress in these technologies, as well as in the fitting techniques of prosthetists, has changed the traditional attitudes toward electric hands. Only a decade ago, electric hands were considered very specialized prostheses, and were rarely prescribed. Now, in up-to-date clinics serving arm amputees in the U.S. and Europe, the majority of arm prostheses utilize electric hands. In another relevant trend, a new breed of prosthetic specialists has emerged - those who fit upper limb prostheses predominately. These new "upper limb specialists" usually travel to the patient's location, allowing patients anywhere in the country to receive the highest level of prosthetic technology, and to be fitted by an experienced practitioner. The large prosthetic "chains" have such specialists, and smaller independent prosthetic laboratories can contract with either a manufacturer's specialist or a freelance specialist if their own experience is lacking. The electric hand and the Synergetic Prehensor may be used together effectively, as in this example, with the hook providing better purchase on the small cap, while the hand grasps the larger bottle more firmly. No one terminal device meets every need yet, so devices are often interchanged using a quick-disconnect wrist system. For bilateral amputees especially, the electric wrist allows much easier positioning of the hand, although the force generated by the electric wrist is not enough to actually twist off the bottle cap. (Photo courtesy of Motion Control, Inc.) Other new electric prostheses include the Utah Arm 2 (U2) by Motion Control, which reworks the sophisticated prosthesis with new sturdier circuit technology, stronger plastics for more rugged use, and new nickel-metal-hydride batteries for faster charging and longer wear. New technologies like the U2 offer consumers dependability and high performance with very little effort compared to that required for body-powered arms.
Body-powered developments and cosmetic covers Though progress in body-powered prosthetics is not celebrated as much as the high-tech electric arms, advances in this technology have the potential to reach many more amputees worldwide. The lightweight Advantage Arm by Sarcos, Inc., features internal cables that go directly from the harness into the top of the elbow unit. In addition, the flexible polymer cables that are used pull much more smoothly than steel cables. A mechanism inside the elbow allows "cable recovery," which means that after locking the elbow with a second cable, the wearer relaxes the pull on the elbow cable, then pulls again to open the hook or hand.
Another new mechanical elbow system, the Automatic Forearm Balance (AFB) features an internal spring-assist mechanism to lift the elbow. The wearer uses a "ballistic" motion to initiate lifting the elbow (i.e., from an extended hanging down position, the wearer will swing the elbow forward). At that point, the "forearm balance" kicks in and raises the elbow to a level position. One version of the AFB, called the Ergo Elbow, is designed to be used with the electric hand. Such hybrid systems, which combine a mechanical elbow with an electric hand, might offer lower weight and the independence of elbow and hand function. The Otto Bock Ergo Elbow is designed to be combined with an electric hand. No wires run outside the elbow. Silicone hand covers Silicone hand covers are now much higher in quality than those previously available. Prior to just a few years ago, the natural-looking silicone covers were not durable enough to be used with electric hands, which could pinch through the glove with their high force. Now, several manufacturers make high-strength silicones for the more functional electric hands, providing the best combination of high grip strength and near-natural appearance.
Fitting improvements for high-level shoulder amputees With the improvements in electric elbows, hands, and wrists, it has become possible to provide more function to even the most-challenged arm amputees - those who have amputations at the shoulder level. Prosthetists are also learning new ways to fit these difficult cases using new easily-formed yet strong plastic materials, which make new, innovative designs possible. A new shoulder component, the LTI-Collier Locking Shoulder Joint, also allows wearers to securely lock the shoulder to prevent front-to-back motion. When they want they can unlock it with a lever pushed with their other hand or chin to freely move the arm to other positions. Shoulder amputees are finding more success now with electric components, since better prosthetic techniques hold the prosthesis more securely on their body. Summary Arm amputees, who struggle to balance the needs of function, comfort, appearance, and cost of their prostheses, represent a great challenge to the manufacturers and prosthetists seeking to satisfy those needs. The fact that arm amputees represent a small fraction of the total prosthetic market discourages advances for several reasons. Besides the obvious economic problem, there are also the difficulties of educating decision-makers and prosthetists about the benefits of new technologies. Nonetheless, two trends are working to the advantage of arm amputees:
2. The trend toward specialization of prosthetic practice has resulted in an elite group of arm specialists and prosthetists whose motto is "Have Tools - Will Travel." Some are sponsored by manufacturers; some work for the major prosthetic service companies, and some are notable freelance independents. They provide the link needed to disseminate modern fitting techniques and the knowledge of the full range of electric and body-powered arm components. New techniques for fitting shoulder amputees, combined with more comfortable materials (ProFlex with Silicone pictured, from Fillauer, Inc.), allow much more successful suspension to proximal level amputees. (Photo courtesy of Advanced Arm Dynamics) Companies mentioned in "Advances in Arm Prosthetics" Motion Control, Salt Lake City, Utah Fillauer, Inc., Chattanooga, Tennessee Life-Like Laboratory, Dallas, Texas Hosmer, Inc., Campbell, California Sarcos, Inc., Salt Lake City, Utah Otto Bock Health Care Aesthetic Concerns, Middletown, New York Rimjet, Inc., Sarasota, Florida Liberating Technologies, Inc., Hopkinton, Massachusetts Advanced Arm Dynamics, Rolling Hills Estates, California
Harold H. Sears, PhD, is general manager of Motion Control, Inc., Salt Lake City, Utah. |
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