Externally Powered Prosthetics/ Orthotics Systems for Children: Present United States Status

John Lyman, Ph.D.

In this country the clinical application of children's prostheses and orthoses which are powered externally has been a rare and generally unsatisfactory occurrence. To the present it is probable that for children 14 years of age or younger fewer than 100 fittings of externally powered prosthetics systems have been made; and virtually no fittings of externally powered orthotics systems. An estimate of 50 actual child users of external power in the U.S. would be optimistic. With respect to prostheses the U.S. experience is in sharp contrast to that of Canada, Great Britain and various European populations where several hundred children have been fitted, in many instances with impressive success in terms of functional regain. Experience with externally powered orthoses in other countries has been essentially similar to our own.

As is well known, the impetus for the extensive use of external power in foreign populations came about in the early 1960s because of the thalidomide tragedy. But, while the relatively sudden appearance of a large number of congenital amputees sparked the initial interest, several factors have contributed to the direction taken by the technology that has emerged-a technology that has placed special emphasis on the use of external power for children's prostheses. The first of these factors stemmed from a general desire to do something special for the thalidomide children by achieving a breakthrough in the state of available appliances.

While the 1950s saw a major change in the prosthetics art through the use of aircraft materials and techniques in the United States, this change did not substantially affect general practice elsewhere. With a few notable exceptions, leather, wood, and, to some extent, light metals dominated foreign prosthetics designs; the upper-limb devices available were generally not designed for active function but as passive replacements with limited cosmetic utility. The chance to take a big step forward from the relatively primitive upper-limb replacements available was a compelling challenge and the political climate was right. The pioneering development of gas-powered upper-limb prosthetic systems by Marquardt5 and his associates at Heidelberg University had achieved considerable success in the rehabilitation of adults. The structure and actuators for pneumatic systems were lightweight enough to be adapted to children and crustacean-type plastic-socket structures could be efficiently fabricated using technology adapted from the U.S experience. Control valves and containers for the gas to power pneumatic devices were readily available. Within two years of the discovery of the thalidomide-caused population, virtually all countries affected were developing pneumatically powered devices along the general lines of the Heidelberg designs. The emotional wave was high and cost was not a restrictive consideration.

A second factor in the extensive development and use of externally powered prosthetic systems in Britain, Europe, and, to a slightly lesser degree, in Canada has been the manner in which the delivery of services has been organized. Powered limbs generally require more maintenance than conventional prostheses, partly because they are inherently more complex and partly because the source of power must be continuously available If the patient must travel long distances for repairs or has to wait for prolonged periods while his prosthesis is being repaired, he will quickly tend to become a non-wearer. The availability of power for electric prostheses is not as critical a problem as batteries can easily be recharged almost anywhere. However, electric devices tend to be even more complex and malfunction-prone than pneumatic units.

To solve maintenance and power-availability problems relatively large-scale resources must be provided for each patient over his lifetime. The prosthesis care and delivery system in Great Britain may be used as an example of the way in which this task is accomplished. The system applies to both children and adults but for the present purpose we will only consider children. A child is fitted at one of several regional centers and provided with a program of training and indoctrination at the center until he is proficient in all of the functions of which he is believed capable by his physician and therapist. On leaving the center the patient is supplied with a complete duplicate of his prosthetic system together with a stock of 42 bottles of C0 2 and prepaid mailers for both his prosthesis and his gas bottles. The turn-around time for the gas supply is about one week; the turnaround time for prosthesis repair may run to several weeks but if, in the meantime, the second prosthetic system breaks down and is also sent to the center, its repair will be given top priority and a functional system will be returned immediately. Incidently, a record is kept of the amount of gas used by each patient and this statistic provides a simple, useful index of the extent to which the prosthetic system is used. Variations on the maintenance system described are found in Europe and Canada. The essential point is that, without an organized follow-up for maintenance coordinated in an efficient social apparatus, no prosthetic (or orthotic) system, however sophisticated, can be expected to produce successful habilitation over the long run.

Money cost has only been referred to briefly in connection with the thalidomide episode and the emotional reaction which led to costs being virtually ignored. Both direct and hidden costs are necessarily high for the habilitation and rehabilitation of orthopedic problems in children whether officially recognized or not. As Lambert 3 has pointed out, because of growth a child needs a new prosthesis annually up to the age of five years, biennially from age 5 to 12, then one every 3-4 years until adulthood. Accurate estimates of cost cannot be made realistically because of many complex interactions involving the private and public sectors of society. If the child becomes an adult taxpayer, costs to the public sector may be recovered; costs to the private sector, in all likelihood, will not. So far as external power is concerned, the one thing reasonably certain is that the money costs for the equipment and its maintenance will easily be three times that of conventional equipment, and sometimes more. Unless these extra costs are offset by sufficient additional functional regain to assure a high probability that the patient will be more productive vocationally after he reaches adulthood, the extra commitment of money cannot be justified on a cost-effective basis alone. Increased patient satisfaction, personality adjustment, and related factors must certainly be considered On the basis of general social conscience, political expediency, etc., rather than on cold-blooded engineering and medical analyses, the necessary money costs may be justified. In other words, in matters such as we are discussing, the metafacts may provide utilities that dominate the facts.

To date, agencies in the United States have not chosen to take up the question of habilitation and rehabilitation of the orthopedic problems of children head on-to treat the problems systematically on the scale that is required and to arrange for provision of adequate organizational and economic backup. In the field of external power there are no U.S.-made components or systems for children which are commercially available. Otto Bock, Inc., and Viennatone both produce powered hands in women's and youth sizes for sale in this country, but these units each weigh over a pound and do not appear to have any utility whatsoever for children under 14 years of age. Components that have been used in American clinics have been "leftovers" from research programs, locally fabricated, special experimental devices or have been imported. The result of this situation is that reliable statistics and quantitative comparisons of the functional utility added, say, by a powered elbow, with an otherwise conventional fitting, are not available. At best the matter comes to the level of individual case studies.

With respect to acceptance or rejection of power-assisted prostheses we are again largely in the dark. Lundberg and her associates 4 at Children's Hospital, Newington, Conn., have recently reported on experience with six children fitted with C0 2 -powered equipment imported from Germany, indicating that all but one accepted and used their powered equipment. The length of follow-up time after fitting and training was not indicated. The authors, recognizing the maintenance problem, state:

"Facilities for servicing C0 2 equipment should be reasonably available When this sophisticated equipment gets out of order, it requires more than the services of an interested mechanic If the prosthetic shop is more than a day's travel from the patient, the practicality of the prosthesis is easily lost."

In a more extensive study, Robertson 7 made visits to the homes and schools of 53 children who had been fitted with upper-limb prostheses at The Children's Prosthetic Unit, Queen Mary's Hospital, London. Fifty-five percent of the children who had been issued bilateral upper-limb prostheses were still wearing them, compared with 80% of the children issued a single upper-limb prosthesis. These results must be qualified by the fact that among the 30 wearers included in the interviews 17 had been fitted with conventional prostheses; i.e., only 13 were fitted with gas-powered arms. It is of particular interest to note that of the children wearing upper-limb prostheses ten wore them routinely all day, twelve wore them only at school and eight wore them only occasionally or for specific activities. The majority of those wearing the C0 2 -powered systems used them only while at school. There are many factors that must be taken into account regarding acceptance but, above all, useful function coupled with the motivation to put up with the inconvenience of the "gadgetry" are predominant. Let us look now at some of the technical aspects of powered devices for children.

Ideally, a prosthesis or orthosis should be considered as a replacement, an intimately associated part of the patient's body, not simply an assistive nuisance. In the ultimate situation, the replacement system would indeed become so much a part of the patient that it would be with him 24 hours a day, just as an implanted hip or knee prosthesis is. Unfortunately, cybernetic technology has not advanced to this point and cannot be expected to do so within the reasonably near future. When and if we do reach such a happy state, it will undoubtedly be with external power. The problems of children's devices are especially difficult to solve not only because of the factor of growth but also because of the child's size and strength levels. While it has been possible, in some cases, to devise self-suspended, self-contained power, control and drive systems for adults, such systems have neither been available nor suitable for children below the age of 14 years. Fig. 1 shows that even the search to find a place to locate the gas bottles is not a trivial matter. Each small-sized bottle weighs in excess of 1 pound and the larger-sized bottle may weigh nearly 3 pounds. Socket fit, choice of control sites, and both suspension and control harnessing all interact to determine an optimum configuration for each patient. Extensive covering of the body may produce intolerable discomfort from thermal causes and/or pressure points. Since externally powered devices are inherently heavier than their conventional counterparts, every effort to produce lighter structures must be made. A good example of a deliberate effort to maximize strength and lightness while still achieving adequate support is shown in Fig. 2 . The Chailey Harness, developed by Ring 6 , is made of carbon-fiber reinforced plastic, a material which has a stiffness that is four times that of metal per unit weight with relatively little loss of strength. It is suitable for high above-elbow amputations, shoulder disarticulations, and some congenital abnormalities.

While cosmesis must necessarily take second place to function, especially with children, appearance can often be improved with little additional weight or structural cost as is shown in Fig. 3 . In the survey by Robertson 7 , appearance was more important to the parents than to the children.

The payoff for acceptability ultimately depends on the total-system's capability for providing functions that would not otherwise be available to the child and which are of substantial use to him. If control of such functions requires great effort and a high attention load, the child may get frustrated and discouraged to the point of rejection even though the system is capable of performing properly. There have been literally dozens of control schemes developed with the aim of allowing the patient to achieve unconscious control. With only one exception, to my knowledge, each available scheme, whether an on-off or proportional switch, produces a rate of motion for a given controller position. Fig. 4 shows some typical gas control valves. The joystick control may have the unique advantage that dual motions can sometimes be achieved simultaneously by choosing an appropriate angle vector. Normally, however, with the attention required by rate control, motions are performed sequentially rather than coordinated in parallel. Fig. 5 shows a valve operated by the acromion and fig. 6 shows an arrangement for using phocomelic fingers for control.

The exception is the system which has been worked out by David Simpson at the Orthopaedic Bioengineering Unit, Princess Margaret Rose Orthopedic Hospital in Edinburgh, Scotland 8 . Since 1965 he has used single- or double-acting pistons as actuators arranged to operate as force-position servos. The operator is given direct feedback of position from the angle through which the joint moves, as a result of his input, and of load in terms of the input force he has had to apply. Simpson observes that with his system the operator feels as though he is a part of the arm, that is, he has a mental image of the arm position much as an experienced driver has a pretty good idea where the boundaries of his automobile are. Simpson calls this type of control system e.p.p. for "extended physiological proprioception." He states that it takes only about one hour of practice before the child is proficient with the system, obtaining coordinated four-degree-of-freedom movement, plus prehension. His service unit has had one of the lowest, if not the lowest, patient rejection rate anywhere.

In summary, it appears that in the United States, as of Spring 1973, we have not established either the commercially available technology or the delivery and maintenance follow-up systems necessary for successful fitting and for achieving patient acceptance of externally powered systems applied to children's neuromuscular problems.


Illustrations used for Fig. 1 , Fig. 3 , and fig. 6 were taken from an article by Jean-nette Hutchison 2 ; Fig. 2 by N. D. Ring 6 ; and Fig. 4 and Fig. 5 by C. Corriveau1. Our thanks are expressed to these authors.

University of California Los Angeles, California

1. Corriveau, C, Prosthetic principles in upper-limb externally powered prostheses. In Aitken, G. T. (ed) The Child with an Acquired Amputaiion National Academy of Sciences, Washington, D.C., 1972, pp. 96-112.
2. Hutchison, Jeannette, The training of upper-limb amputees with conventional and externally powered prostheses In Aitken, G T (ed) The Child with an Acquired Amputation. National Academy of Sciences, Washington, D.C., 1972, pp. 139-159.
3. Lambert, C. N., R. C. Hamilton, and R. J. Pellicore, The juvenile amputee program: Its social and economic value. J. Bone and Joint Surg., 51-A:6:1135-1138, September 1969.
4. Lundberg, Constance, S. W Paul, E. E VanDerwerker, and J C Allen, Experience with carbon-dioxide-power-assisted prostheses Inter-Clin Inform Bull., 12:1:1, October 1972.
5. Marquardt, E., The Heidelberg pneumatic arm prosthesis. J. Bone and Joint Surg., 47-B:3:425-434, August 1965.
6. Ring, N. D., The Chailey harness with carbon-fibre reinforced plastic. Inter-Clin. Inform. Bull., 11:3:5, December 1971.
7. Robertson, Elizabeth S , Follow-up study into the functional abilities at home and at school of multiple limb deficient children London: Queen Mary's Hospital, Roe-hampton, February 1971.
8. Simpson, D. C, and G Kenworthy, The design of a complete arm prosthesis. Biomed Eng., 8:2:56-59, 1973.
Descriptors: External power; prosthetics; orthotics; children; gas-powered; electrically powered; C0 2 .