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Chapter 12D - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles Special Considerations: Trends in Upper-Extremity Prosthetics Development
Harold H. Sears, Ph.D.
INTRODUCTION AND BACKGROUND
Research and development of arm prostheses has historically been spurred either by great tragedies such as wars and birth defects or by the introduction of new technologies that allow new solutions to persistent problems. One can only hope that new technologies, supported by a more enlightened valuation of amputees' needs by society, will provide sufficient motivation in the next decade.
The Post-World War II Era
The late 1940s and early 1950s saw the application of new materials that had evolved from the aircraft and other industries during the war. Steel cables applied in the classic Bowden bicycle-type cable allowed the replacement of leather thongs and inefficient pulleys. Aluminum manufacturing made hook-type terminal devices more durable and light, and neoprene linings made of improved rubber materials allowed better fric-tional surfaces. Laminated sockets made of new resins with fiberglass and other materials allowed better-fitting, lighter-weight, and cosmetic sockets to be made for arm prostheses without long hours of hand labor. Locking elbow joints made of aluminum and steel finally provided active positioning with locking at the elbow for the transhumeral (above-elbow) amputee.
External Power Beginnings
In the late 1960s and early 1970s, the first generation of portable batteries, electronic circuits using transistors, and small electric motors allowed the first electric hands to be developed by the Viennatone and Otto Bock Company in Europe and the Veterans Administration/Northwestern University (VA/NU) electric hand in the United States. The Otto Bock hand survives from that era, although much changed and improved since its earliest versions.
Early electric elbows were developed at Massachusetts Institute of Technology (MIT) (sponsored by Liberty Mutual Insurance Company), as well as the Veteran's Administration, Rancho Los Amigos Hospital, the INAIL (Officina Orthopedia per Invalidi del Lavoro) Center in Italy, and several other centers.
Second-Generation Externally Powered Devices
Evolution of smaller, more powerful electric motors and better batteries allowed both hands and elbows to evolve to a more natural-appearing prosthesis. As mentioned, the Otto Bock hand became more efficient, with sufficient miniaturization so that a completely self-contained transradial (below-elbow) prosthesis can be made for most amputees. Very ambitious multiple-motion hands such as the Sven hand in Sweden as well as others in Yugoslavia, Japan, and Canada were developed. These hands, with a much more anthropomorphic design of multiply hinged fingers, have not yet proved to be commercially feasible.
The Utah Artificial Arm, a transhumeral prosthesis offering proportional control of both hand and elbow, utilized advanced techniques for electromyographic (EMG) control applied in a practical way via miniaturized electronics. Modern injection-molded composite plastics offered a strong but very light shell, while a modular design allowed rapid serviceability and upgrades as the design evolved.
Other electronic elbows include the Boston Elbow,the first proportionally EMG-controlled elbow, and a much less complex elbow developed at New York University (NYU). Providing a much simpler, lower-cost alternative, the NYU elbow has been used primarily as a switch control device. The one-speed drive simplifies both control and mechanism, although sacrificing a number of features.
Approaches Developed for EMG Control
Evolution of transistorized circuits finally allowed practical EMG amplifiers to be used in a prosthesis. Computers allowed researchers to investigate more sophisticated control methodologies in an effort to create a naturally performing arm with multiple degrees of freedom. Simpson and others, faced with the challenge of hundreds of thalidomide-induced birth defects, were the first to attempt a method of "natural" extension of remnant limb function called extended physiologic proprioception (EPP) by using pneumatic actuators without a great deal of electronic sophistication. Pattern recognition was an alternate technique that attempted to recognize the intent of the amputee based on the pattern of EMGs from several muscles in the remnant limb. Statistical analysis of the EMG from a single muscle by using autoregressive moving average (ARMA) techniques was attempted at the University of Illinois. Jacobsen's postulate control, pursued at the University of Utah, is based on the ability of the EMG to linearly predict the force in a muscle and thus for the muscles of the shoulder to predict the torques about the shoulder of the amputee. With the estimated force information, the commands to the prosthesis are computed by using kinematic equations of a normal arm linkage to produce a more or less "natural" control of the limb. Although no arms with simultaneous multiple degrees of freedom are commercially available, some of this work provided a theoretical basis and test bed for products that were eventually commercially available, e.g., the Utah Arm, and may form the basis for other developments in the future.
Sensory Feedback Systems
Several research groups have developed laboratory-tested systems and have even field-tested prototype feedback systems extensively. The group at the University of New Brunswick utilized an electrotactile display to the amputee, which represented the pinch force of the thumb vs. the first finger of the hand. A nerve stimulation technique was utilized at Duke University, with a telemetry system transmitting across the skin so that the stimulation of the nerve would be proportional to the pinch force on the tips of a hook terminal device. Some prototypes from the early field tests remain in place today. A vibrotactile skin interface was utilized by Shannon in Australia, who sensed pinch force of the hand tips via strain gauges. At the University of Utah, experiments were conducted with a mechanism that simply pushed against the skin with a force proportional to the pinch force at the tips of a hook terminal device. This method was dubbed extended physiologic taction (EPT). Laboratory tests demonstrated that this simple feedback was capable of improving a subject's control over the terminal device to near-normal levels.
None of the experimental systems described have achieved widespread commercial application due to limitations such as size, cost, technical stumbling blocks, or the lack of extended funding necessary to develop a practical system.
Terminal Device Development
Several new hook-type (or "nonhand") terminal devices have resulted from research in the 1970s. The Child Amputee Prosthetics Program (CAPP) terminal device, the work of the late Carl Sumida of UCLA, introduced replaceable soft plastic covers and a center-pull cable actuation, although some object to the "lobster claw" appearance. The Grip terminal device by Therapeutic Recreation Systems was the first new voluntary-closing terminal device to be offered since the American Prosthetic Research Laboratory (APRL) hook and hand developments of the early 1950s. The Grip voluntary-closing approach has now been expanded to child sizes as well as adult versions.
Other terminal device innovations have included the ACRU hook with classic Dorrance-type finger shapes, plus a special adapter attached to the user's own tools, and the "Contour Hook" by Hosmer, Inc. A myoelectric hook drive developed at Northwestern University in the early 1970s utilizes classic "lyre-shaped" hook shapes powered by a two-motor, two-speed drive that allows quick operation as well as a slower, high-force mode. This has been dubbed "synergetic" drive.
FEASIBLE DEVELOPMENTS WITHIN 10 YEARS
Body-Powered Arm Systems
Although the "sound and fury" over the last two decades of upper-limb prosthetics research has been generated by externally powered arm and hand research, a resurgence of interest in body-powered arm systems is beginning. It is apparent that externally powered systems have limitations in distribution (primarily due to a lack of third-party funding) and in applications in extremely rugged situations where environmental conditions would damage electronic components. Also, the weight and maintenance of a precise socket fit remain drawbacks to most myoelectric systems.
New materials have raised the possibility of more efficient actuation of body-powered systems. Fibrous cables woven of extremely high strength polymers promise to make possible a more efficient body-powered system of lighter weight. Better cosmesis may also be possible due to internal routing of the more flexible fibrous cables.
The new body-powered elbow under development at the University of Utah seeks to implement internally routed fibrous cables in a new mechanism that will allow cable recovery, i.e., limited cable excursion can be "reused" by a rachet-type mechanism. Strong and lightweight plastic shells are also in development, as well as plans for a multidirectional wrist.
Children's Hospital at Stanford has experimented with hydraulic actuation in which hydraulic pressure generated by a harness pull (usually between the amputee's scapulae), allows a hydraulic "slave" to drive the terminal device and/or other motions. A flexible tube containing hydraulic fluid connects the cylinder in the harness with the terminal device. At this time, however, hydraulic actuation is not considered to be practical by the Stanford group.
An alternative harnessing technique for transradial prostheses evolved from a student design project at Stanford. Triceps power capture (TPC) harnessing utilizes a latch that harnesses elbow extension directly to terminal device opening, but when unlatched allows the elbow to swing freely. The evaluation reports the expected benefit of freedom from shoulder harnessing, although accompanied by the awkwardness of the operation of the latch. Work at Delft University also seeks to harness elbow extension to operate a children's-sized hand that could be more comfortable and cosmetic by eliminating the shoulder harness.
Novel pulley-routing methods to eliminate the external cable housing (which adds weight and interferes with clothing) have been the topic of private investigations by arm amputee Joe Ivco. He too seeks a more efficient and lighter-weight cable actuation mechanism (see Fig 12D-1.).
The "lift pulley" by Carlson (see Fig 12D-2.) is another simple device that could increase the efficiency and lifetime of a body-powered control cable by eliminating the sharp bend of the traditional lift tab. Preliminary results by Carlson indicate from 20 to 100 times longer cable life over this particular wear point.
Terminal Device Designs
New materials and new designs hold the promise for improved terminal devices. Much current work continues to focus on nonhand approaches. A Stanford design (see Fig 12D-3.) allows both voluntary-closing and voluntary-opening actuation in a nonhook, nonhand pre-hensor shape. The CAPP terminal device is currently being developed in an adult size to allow a continuous utilization of this same terminal device shape by those amputees who started with the CAPP children's device. The Utah Terminal Device, developed by the author and others at the University of Utah (Fig 12D-4.), was designed to offer more efficient gripping shapes without sacrificing the advantages that have been proved in the Dorrance-type hooks.
New terminal device designs have several features in common, notably the application of modern materials to improve the weight, durability, and appearance of traditional hook-type terminal devices. There is promise that modern plastic materials may provide enough strength to replace the heavier metal terminal devices of the past, with more cosmetic colors and potentially greater durability of gripping surfaces utilizing newer polymer coatings rather than rubber. Present voluntary-closing, i.e., pulling the cable closes the hook, terminal devices may be improved and new versions available in the future. The Utah Terminal Device has been developed with the capability for a voluntary-closing mechanism as well as a voluntary-opening one.
Carlson at the University of Colorado in Boulder has also done work on a "holding assist" for body-powered terminal devices as well as a "synergetic" mechanism that could drive both a fast and slow (but more powerful) finger of a voluntary-closing terminal device.
Structures for body-powered arms may also be improved by the application of new materials. The experience with some myoelectric devices, e.g., the Utah Artificial Arm, has shown the potential for exoskeletal structures of modern composite plastics (reinforced with fiberglass and graphite). Surfaces can be smooth and aesthetic and yet allow the hollow interior to be used for routing of cables or installation of more efficient actuation mechanisms. Research at the University of Utah as well as other centers seeks to apply exoskeletal structures in body-powered prostheses.
Other components that may be improved by the application of new materials and design include the shoulder joint, which could potentially have a controllable lock to allow better positionability of the prosthesis at the shoulder joint. Micacorp, Inc. (Longview, Wash), is currently manufacturing a lockable shoulder joint, and Northwestern University has announced the development of a shoulder joint also. Prototype shoulder joints developed at the University of Utah that lock in 2 degrees of freedom are shown in Fig 12D-7..
Wrist components, positionable in multiple degrees of freedom, also are under development at the University of Utah. Studies of terminal device function have shown that since man-made devices have limited prehension capabilities, it is imperative that the amputee position them precisely for each particular prehension task. Lack of positionability at the wrist significantly limits the function available from any terminal device.
Socket Designs for Transhumeral and Shoulder Disarticulation
Modern materials for sockets may allow improvements in the comfort and weight required to be suspended on the amputees remnant limb. Flexible materials either molded (such as room-temperature vulcanization [RTV] silicone materials) or vacuum-formed (such as Surlyn and others) are being used regularly in lower-limb prosthetic sockets and are beginning to be applied to upper-limb sockets as well. Greater flexibility reduces hard edges and surfaces and allows the prosthetist to experiment with more intimately fitting techniques that promise better comfort, just as a snug-fitting ski boot provides better comfort and control than a loose one. New fibers such as Kev-lar, Spectra, and improved fiberglasses should allow prosthetists to make lighter-weight and stronger sockets since fewer layers of material will be required. Breathability, i.e., allowing amputees greater transpiration of heat and perspiration, may be possible eventually. Variations on the traditional double-wall socket are being explored currently by incorporating a flexible inner socket with a "skeletal" outer suspension. Much of the medial surface of the socket can be single walled, which proves to be somewhat cooler. New transhumeral socket shapes are also being developed with the more flexible materials mentioned above. Sockets narrow in the mediolateral dimension for transhumeral amputees apply techniques evolved for the new-style "ischial containment" sockets for transfemoral (above-knee) amputees. Such intimate-fitting sockets can often be self-suspending as well. Self-suspending suction sockets, routinely fitted to transfemoral amputees, have also proved feasible for some longer transhumeral amputees. Shoulder disarticulation designs are evolving to utilize newer, lightweight vacuum-formable materials and techniques that transfer the weight of the prosthesis over the load-bearing areas of the shoulder, with stabilizing "wings" around the lower part of the rib cage.Computer-aided design/computer-aided manufacturing (CAD/CAM) techniques being developed for the lower limb may soon be applied in upper-limb sockets. Sensing shapes for a transhumeral socket may be awkward since a circumferential apparatus will not be possible with the remnant limb in an anatomic position. Transradial sockets, however, should be feasible. The other promise of CAD/CAM techniques is easy modification of the shape by using the digitized image. Part of the challenge of using CAD/CAM techniques will be the intimate fittings being sought in the upper limb, especially for myoelectric prostheses.
External Power
The application of external power to artificial hands and elbows, thus eliminating the control cables (the most unpopular feature of body-powered arms), has had a great impact on upper-limb prosthetics in the last two decades. However, most commercially available devices must be considered firstor second-generation technology, and the next decade should see many continuing improvements on what has been an encouraging start.
Power Sources
Since batteries are a multibillion dollar consumer industry, this technology can be expected to continue to advance in the next 10 years. The technical improvements have increased the capacity of rechargeable batteries in recent years. Also, disposable alkaline batteries have become a viable alternative for many amputees. Recharging is not necessary, and the price per battery is usually low enough to compete with an expensive rechargeable battery pack. Whether rechargeable or disposable, the use of readily available consumer batteries is expected to become more and more commonplace.
Although pneumatic and hydraulic power sources are still considered in some centers, their application to arm prosthetics is not expected to expand due to the convenience of batteries and electric motors.
Control Methods
Nearly all of the currently used myoelectric prostheses utilize the classic two-site agonist-antagonist control method. This is the most physiologically natural control and is usually easy for an amputee to master. Research should improve some of the remaining difficulties. Improved resistance to electrical interference from outside sources is possible and would improve the performance of most myoelectric systems. The problem of inconsistent contact of electrodes with skin could be improved by the combination of more intimate-fitting socket designs plus improved electrode designs. Internally implanted EMG electrodes that transmit the EMG signal across the skin via telemetry have been used experimentally at the University of Alberta and may hold promise for the future since they eliminate the problems with the skin-electrode interface. Some work in this area continues at the University of New Brunswick. However, the issues of biocompatibility and additional surgeries are drawbacks for most patients.
Present externally powered arms offer powered degrees of freedom at the elbow, wrist, and hand. However, simultaneous control of more than 1 degree of freedom is not easily accomplished. As mentioned previously, despite extensive research in the past on several methods for control of multiple degrees of freedom, no practical application is currently available commercially. The postulate-based control developed at the University of Utah could possibly be refined into a practical system by simplifying the 14-muscle approach of the laboratory to a 4- to 5-muscle clinical system. Postulate control could conceivably provide simultaneous control of 2 or 3 degrees of freedom in a single prosthesis. Note that both postulate control and pattern recognition approaches require multiple EMG sites as well as a sophisticated calibration procedure to the amputee and the EMG signals that are produced.
Extended physiologic proprioception (EPP) is again being pursued as a method for providing control over an electric-powered motion by using the innate controllability the amputee has over an existing more proximal joint. For instance, the remnant motions of the shoulder or humerus could be used for patients without good control over residual EMG signals. Sensors for the tension in a control cable have been developed that use either load-cell-type force transducers or force-sensitive resistive material. Practical experiments have controlled an electric elbow by converting the force information to a command for the elbow. A mechanical link to the elbow-forearm motion is provided by connecting the control cable directly to the forearm around a pulley, as shown in Fig 12D-5. and Fig 12D-6.. This provides the "physiologic proprioception" of Simpson's theory, like power steering on a car, so that the position sensation is provided, although little actual force is required.
Fortunately, existing electric elbows will be adapted easily to a position controller input. The previously mentioned EPP controllers have been demonstrated with the Boston Elbow and the Hosmer Elbow. Fig 12D-7. shows position-controlled versions of the Utah Arm also. The joystick-type sensors actually control 2 degrees of freedom simultaneously by a bilateral fore-quarter amputee. Locking shoulder joints designed, with the other components, at the University of Utah, demonstrate the practicality of the concept and the large work envelope possible with them.
Position control and EPP are not without their drawbacks, however. Dedicating a remnant body motion to one or more motions of the prosthesis may involve a sacrifice of natural function for some patients. Also, if the shoulder motion (protraction) in longer transhum-eral amputations is dedicated to elbow control, then a second independent direction of shoulder motion must be harnessed for control of prehension. Alternatively, myoelectic control could be used from biceps and triceps, if available. Although EPP is certainly a feasible approach for control of multiple degrees of freedom, it is difficult to envision any significant simplification or reduction of the challenge. Any approach will require sophisticated control logic and electronics as well as multiple motors and an external power source.
By using time series analysis methods similar to Graupe's work described earlier, the group at the University of New Brunswick has claimed good success at distinguishing separate functions from a single EMG signal. When a computational technique known as a Hopfield network is used, the EMG signal can be rapidly analyzed and represented as a time series with numerical parameters that vary according to the function performed by the muscle (the biceps or triceps in this case). By using another mathematical device known as a "perceptron" the parameters can be analyzed to distinguish among the functions performed by the muscle, e.g., elbow flexion, elbow extension, and forearm pronation and supination. This method awaits a practical field trial, where muscle intent may be more difficult to decipher.
Externally Powered Hands
Progress is likely in externally powered hands because in this area (more than others) developments may be "market driven." Since amputees have a strong desire for improvements and since all prostheses require some type of terminal device, the market is large enough that manufacturers may realize a return on their investment. This area is also promising because several technical improvements are feasible.
Electric motors continue to improve each year. Innovations such as brushless dc motors and cobalt samarium magnets are lowering the size and weight required to deliver a specific torque output. Improved motors will allow not only smaller and lighter hands but also more efficient energy consumption for longer battery life.
Composite/plastic structural materials also offer promise for lowering the weight of artificial hands when used to replace metal structural elements and gearing. Heretofore, plastic materials have not had equivalent strength-weight ratios to metals, but the gap is narrowing.
New design approaches in hands should provide a greater range of gripping modes. Examples include the hand under development at Princess Margaret Rose Hospital in Scotland, as well as other hands under development that promise a compliant grip, (i.e., fingers that curl around an object). A modular system of knuckle and thumb drives is planned so that as many as six sizes could be produced from symmetrical structural components. A wrist-driven child's hand is also being produced (Fig 12D-8). Silicone production gloves are under development also, with the goal of more cosmetic and cleanable gloves (Fig 12D-9.). It is also likely that hands with tip prehension between the thumb and first finger will be developed so that two fingers may have a key-grip-type prehension that has not been available in electric hands.
Variations of currently available hands will be seen, likely with added improvements in reliability and lighter weight. The Otto Bock hand in 1990 has been introduced in a child's size with a direct drive from a two-motor, synergetic drive in the palm that eliminates some gearing used in previous adult hands (see Fig 12D-10.). A similar drive will also be made for the adult-sized Otto Bock hand.
Reviving the pneumatic drive approach used in previous decades, work at Delft University in The Netherlands is seeking to develop a child-sized hand powered by small gas canisters. Since greater energy storage is possible in such a canister than in an equivalent-weight battery, a lighter, faster, and smaller hand for children may be possible.
Gloves for externally powered hands should see the use of reinforced silicone materials that are more easily cleaned and more natural looking. A need exists for gloves that are more readily custom-colored to the skin tone of the amputee, as well as gloves that are more easily replaced by the users themselves.
Sensory Feedback in Artificial Hands
Although previously mentioned work showed promise for the feasibility of a practical sensory feedback system, the technology promises to be relatively expensive and thus less attractive for commercial application in an era of cost containment by third-party payers.
Pressure-sensing technologies are under development in the robotics industry, and "spin-off' from that area into prosthetics may make its application in prosthetics possible. Technologies utilizing reflection of light across a thin layer of polymer (polytetrafluoroeth-ylene [PTFE] or Teflon) have been experimented with, as has the application of strain gauges directly to the metallic fingers of an artificial hand.
Presentation of the pinch force information to the amputee is another side of the problem. As mentioned previously, extended physiologic taction (EPT) may prove feasible by using a small "pusher" actuator to present a pressure proportional to the pinch force on the amputee's skin, perhaps within the socket. However, this approach will require the development of a very small actuator that can be installed within a socket. Nerve stimulation has appeared promising in the past, although implantable materials are required that can transduce the action potentials of a nerve over a long period of time. Efficient telemetry electronics will also be necessary to transmit across the skin barrier. Other techniques such as electrotactile and vibro-tactile feedback may be possible as well.
New electric drive modules for upper limbs are being developed at the Princess Margaret Rose Hospital in Edinburgh. A few modules of different sizes are planned that will be used to drive different joints in various sizes of prostheses, e.g., an adult-sized elbow may be also used as a child's shoulder. As shown in Fig 12D-11., the motors will drive linear actuators mounted in a structural framework that will replace the pneumatic actuators in the early "Simpson" arm prostheses of the 1960s and use an updated EPP-type controller.
Partial-Hand Prostheses
One area that has been neglected in prosthetics research and development is the transcarpal, or partial-hand, prosthesis. Development is difficult because of the wide variety of loss suffered by these patients, from single digits to transcarpal. However, the feasibility of miniature motor and drive systems for individual fingers and a thumb has been demonstrated (Fig 12D-12.). Although the weight and size constraints remain daunting, Weir reports that by using a "syner-getic" drive, a pinch force of over 8 lb for each finger and a speed of 2 radii per second have been achieved.Future possibilities of small battery supplies, strong and lightweight plastics, and miniature electronics may allow a practical prosthesis in the future.
Elbow Prostheses
The trends toward smaller motors and improved plastics should also benefit transhumeral amputees. "Hybrid"-type fittings using one or more externally powered joints combined with body-powered components should continue to grow in popularity. An externally powered hand used with a body-powered elbow is commonly fitted at many centers and will be even more feasible when body-powered elbows offering greater efficiency of cable control become available.
Experimental work on EMG control theory is not presently being pursued widely. One might say that the multiple-degree-of-freedom control theories developed and demonstrated by Jacobsen and others await lighter and smaller actuators and computerized implementation.
Some more recent work at MIT uses a prosthesis control emulator to compare control methods for a myoelectric elbow (a Boston Elbow). A simulation of "natural" control was made, i.e., in this case a position controller commanded by the difference of two muscle EMG signals, combined with variable elbow joint impedance (resistance) controlled by the coactivation of the two muscles. The MIT group uses a crank-turning apparatus to compare this type of control with both the natural elbow and the high-impedance controller for the Boston Elbow. They found that their "natural" controller had performance closer to the intact natural elbow. The group hopes to compare other control schemes in the future such as the Utah Arm controller, etc.
Other Components
Improved shoulder joints should eventually be developed. A joint that may be locked or unlocked and repositioned easily by its wearer could add significant function for the high-level shoulder disarticulation or for the interscapulothoracic (forequarter) amputee. Externally powered solutions are being pursued by the Edinburgh group, but the energy and torque requirement to move an entire prosthesis at the shoulder joint is high and requires a large battery supply and large drive unit (see Fig 12D-11.).
Smaller, higher-torque wrist rotation modules seem feasible and attractive to many amputees. Ideally, a wrist rotation unit can be used with wrist flexion either proximal or distal to the rotation joint itself. Current externally powered wrist units require significant length (approximately 2½ in.), which makes installation difficult and makes it awkward to combine with a flexion joint.
External power of humeral rotation should be expected as well since a modular wrist rotation device could conceivably also be used for humeral rotation. However, control of humeral rotation simultaneous with other motions will require a more sophisticated control scheme than those available commercially. Perhaps a simplification of one of the experimental methods for control of multiple degrees of freedom will prove successful.
Direct attachment to remnant skeletal elements may yet see progress in the decade of the 1990s. Experiments conducted by using pyrolytic carbon materialsand hydroxyapatite materials show promise for allowing attachment of man-made materials directly to bone. However, the trans-skin interface may be a more difficult problem since the risk of infection threatens not only the viability of attachment but also the health of the patient.
COMMENTS ON THE RESEARCH AND DEVELOPMENT ENVIRONMENT IN UPPER-LIMB PROSTHETICS
Those interested in the development of new upper-limb prosthetic devices face a predicament: great possibilities without the availability of sufficient resources to achieve them. This shortage of resources can be traced directly to the small size of the patient population. Research funding, usually distributed according to the size of the population of need, allocates but a sliver of total medical research funds for the development of prosthetic devices. Also, industry cannot expect a high-volume return from their development efforts for the small upper-limb amputee population.
Development is also hindered by the fact that traditional reimbursement levels in prosthetics are based on devices made with older technologies, usually with lower manufacturing costs. New devices invariably cost more than the older devices they replace because of the capital costs of starting new products in addition to development costs. This situation is inherently frustrating for both the amputee and the developer, who can see the technology developed for other industries, e.g., aircraft, robotics, consumer electronics, etc., that still awaits application in artificial limbs. For example, an artificial hand with compliant gripping modes, sensory feedback, lifelike cleanable gloves, and a reasonable weight is now technically feasible with presently available technology. However, the price tag necessary to deliver such a prosthesis would probably not be reimbursed by any present funding sources, either private or governmental.
Another effect of the meager funding available for prosthetics research is that very little basic research can be pursued in this area. Rather, prosthetics must adapt technologies from other industries, e.g., electronics, composite plastics, batteries, etc., to problems in prosthetics.
Research centers as well as industrial research also have difficulty gaining and maintaining momentum because of limited funding in prosthetics research. A team with experience and a track record takes several years of continuous work to establish, and discontinuities in funding break up a development team so that the advantage of continuous experience in the field is lost along with the momentum.
However, one positive aspect of prosthetics research is that when new technologies become available, prosthetics is an area where significant progress can be made rapidly. Also, such improvements affect not just the performance of a mechanical device, but have a profound impact on an amputee's life and livelihood. Studies have shown the cost-effectiveness of successful rehabilitation. Potentially this can be used to influence both funding sources and reimbursement sources to value the improvements of research and development for their life-enhancing effects on an amputee. Advanced prosthetics research has the potential to improve productivity, independence, psychological outlook, and general health as a direct result of improvements in technology.
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- Rehabilitation Engineering Center, Children's Hospital at Stanford: Improvement of Body-Powered Upper-Limb Prostheses. Final Report, October 1989.
- Scott RN, Brittain RH, Caldwell RR, et al: Myoelectric control systems-Progress report No. 17. UNB Bio-Eng Inst Res Rep 1980; 80:2.
- Sears HH: Evaluation and Development of a New Hook-Type Terminal Device (dissertation). Department of Bio-engineering, University of Utah, Salt Lake City, 1983.
- Shannon GF: A myoelectrically controlled prosthesis with sensory feedback. Med Biol Eng Comput 1979; 17:73-80.
- Shaperman J, Setaguchi Y: The CAPP terminal device, size 2: A new alternative for adolescents and adults. Prosthet Orthot Int 1989; 13:25-28.
- Simpson DC: The choice of control system for the multi-movement prosthesis: Extended physiological proprioception (e.p.p.), in The Control of Upper-Extremity Prostheses and Orthoses. Springfield, Ill, Charles C. Thomas, 1974, pp 146-150.
- Stein RB, Charles D, Hoffer JA, et al: New approaches for the control of powered prostheses: Particularly by high-level arm amputees. Bull Prosthet Res 1980; 17:51-62.
- Weir RFF: The design and development of a synergetic partial hand prosthesis with powered fingers. Presented at the 12th Annual Rehabilitation Engineering Society of North America (RESNA) Conference, New Orleans, 1989, pp 473-474.
- Wirta RW, Taylor DR, Finley FR: Pattern recognition arm prosthesis: A historical perspective-final report. Bull Prosthet Res 1978; 10:8-35.
Chapter 12D - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
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