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Electric Limbs for Infants and Pre-School Children

Carl D. Brenner, CPO

Throughout the past 20 years, advancements within the field of electronic technology have had a steadily increasing impact on the field of upper-limb prosthetics. This has led to the use of electronic limbs by a broad segment of the adult amputee population as well as by increasing numbers of children and infants with acquired and congenital limb deficiencies. For the purpose of this article, the term "infant" will be used as defined in Stedman's Medical Dictionary: a child under the age of two (1).

The fitting of infants and pre-school children with electronic limbs had its beginnings in Sweden in 1971. At that time, a three-year-old girl named Asa, with a congenital below-elbow (BE) deficiency, was fitted by Rolf Sorbye at the Regional Hospital in Orebro, Sweden. Asa was the first pre-school child to be fitted with a myoelectric prosthesis using a 6 3/4-inch Otto Bock electronic hand (2).

Over the next 14 years, the successful experience in Sweden eventually generated similar activity in a few centers in North America, leading to the next breakthrough in infant electronic fittings. In 1985 a 12-month-old girl named Erin, with a BE congenital limb deficiency, was fitted at the Michigan Institute for Electronic Limb Development in Detroit (see Figure 1 ). Her prosthesis included a two-site, two-function electronic control system and the Systemtechnik electronic hand developed by Sorbye in Sweden (see Figure 2 ) (3). As a full-time wearer and active user of her prosthesis since the age of one year, Erin provides an encouraging example of the benefits to be gained by the early use of an electronic limb (see Figure 3 ).

Practical Considerations and Outcomes

In the past 10 years, more than 200 electronic limbs have been provided to children seen at Detroit's Variety Club Myoelectric Center. The ages of the patients fitted ranged from 12 months to 19 years, with about half of the prostheses provided to children between one and four years of age (see Table 1 ). When the program began in 1981, one of the overriding concerns centered on the expectation of frequent electromechanical failure of the prosthetic components used by small children. At the time, it seemed reasonable to assume that fitting infants or pre- school children with expensive electronic hardware could lead to many costly repairs. Hindsight has shown that those fears were largely unfounded since the electronics manufactured for use by children were very durable, and the children and their families took very good care of this precious equipment. The average frequency of electromechanical failure is about three times every two years (see Table 2 ) (4).

Another major area of concern was the longevity of the prosthetic fit. Before 1986, no technique for building growth liners in electronic prostheses existed (see Figure 4). Since that time, this has become a routine procedure, increasing electronic limbs' useful life by 24 percent (see Table 3 ).

A third consideration in fitting infants with electronic componentry was the total weight of the prosthesis. Since we fit most infants with a passive prosthesis between four and six months of age, they have sufficient time to acclimate to the weight and sensation. Thus far, the rejection rate has been less than two percent, based solely on the weight of the prosthesis (5). A one-year-old child can easily tolerate a prosthesis weighing 12 to 16 ounces (340 to 454 g), and the new lightweight, injection-molded hand, available from Variety Ability Systems Inc. in Toronto, Canada, makes it possible to build a prosthesis that weighs less than nine ounces (255 g) (see Table 4 ).

Lastly, it has become apparent that, of all the prosthetic components that undergo the normal wear and tear of an active child, the most vulnerable has proven to be the outer glove that provides both protection and a cosmetic appearance to the electronic limb. Based on a decade of experience with cosmetic gloves, sstatistics now show that children will require between two and three gloves per year (see Table 5 ).

Limb Banking

No discussion of electronic limbs would be complete without mention of the concept of limb banking (6). A limb bank is a collection of components-consisting of electronic hands, electrodes and electrode wires, batteries and battery chargers-that can provide a ready replacement for any component that is being used by an amputee. Limb banks are generally built up over a period of time as components are outgrown by children and donated to the limb bank by their families. Also, a limb bank can be developed initially by purchasing new componentry to provide additional backup systems when first starting a program. In Michigan, the Variety Club of Detroit has underwritten the original costs of developing a limb bank for the Variety Club Myoelectric Center.

A limb bank's most important benefit is that it reduces the downtime for repairs and maintenance of electronic prostheses. It is essential when providing electronic limbs to infants and children that the amount of time spent out of the prosthesis be held to a minimum.

A successful limb-fitting program must include the capability of doing in-house repairs for any of the electronic systems being used by the patients. In our early experience, it was necessary to ship components to the manufacturer for service, resulting in several weeks of delay before the prosthesis could be worn again. As a consequence, it was found that developing a comprehensive in-house inventory and a staff trained to deal with all electromechanical failures was the best solution. Now 80 percent of repairs and adjustments are completed within two hours or less (see Table 6 ). When a repair cannot be completed within this time frame, a component from the limb bank can be used so the patient still receives the prosthesis the same day.

A second advantage of a limb bank is the opportunity to provide a child with an electronic prosthesis, regardless of a family's ability to pay. Since most of the cost of electronic prostheses is related to the electronic hardware, the use of limb bank componentry in those instances where financial resources are limited can be of tremendous benefit to many families.

A third benefit is patients can use a preparatory electronic prosthesis. While two successful cases, one in Sweden and one in Michigan, have already been mentioned, it should not be assumed that all children or infants are suitable candidates for electronic prostheses. In cases where the' clinic team entertains doubts as to the successful outcome of an electronic fitting, the use of a preparatory electronic prosthesis can be very helpful in identifying the most likely result. Since limb bank components can be used, it is possible to provide a preparatory electronic prosthesis at a fraction of the cost of a totally new prosthesis.

Preparatory electronic prostheses have a three-fold purpose, consisting of preparation, evaluation and training (6). The preparatory objectives include establishing optimum electrode sites, improving myo-signal strength, and conditioning tissues to accept the self-suspended socket and weight of the prosthesis.

By way of evaluation, the preparatory electronic prosthesis helps to validate the practicality of the socket design and selected components, assess the motivation of both the patient and the parents, demonstrate the overall functional value of the prosthesis to the patient and family, and provide clinical evidence to support cost/benefit rationale.

In terms of training, this prosthesis helps the patient discover the operating characteristics of the prosthesis and lets the patient practice appropriate activities of daily living with a properly fitted electronic prosthesis (7). Although a preparatory electronic prosthesis should be fitted with the same care as any definitive prosthesis, the fabrication process and the components used provide a very cost-effective way of analyzing the patient's true needs.

Criteria for Electronic Fittings

The question of when to fit an electronic prosthesis to a limb-deficient infant has yet to be decided. Since applying electronic prostheses at the 12-month age level is a relatively new practice, having emerged within the last five years, the assessment of its long-range implications will not be evident for at least another 10 to 15 years.

While chronological age is the most common quantitative reference used when describing the time frame of intervention, it is the developmental readiness of the individual that is most crucial to a successful outcome. As Wendt and Shaperman indicated in their study of early infant fittings with a cable-controlled hook, each infant has his or her own timetable of neuromuscular maturation (8). Until the child reaches that level of neuromuscular potential, it is unlikely an activated prosthesis will provide additional function.

Based on the original research conducted by Halverson and Gesell, and more recent investigations by Erhardt, it is reasonable to assume that normal prehension in an infant is developed somewhere between 12 and 15 months of age (9-11). However, the findings of Halverson, Gesell and Erhardt focus primarily on unilateral development, leaving questions of bimanual function unanswered.

Aside from the issues associated with normal human development, psycho/social dynamics-particularly at the family level- can have great influence on the long-range results of early prosthetic intervention. As pointed out by Brooks and Shaperman in their study of infant prosthetic fittings, most children who reject a prosthesis do so because of their parents' lack of support and participation (12). Sorbye also identified the significance of positive parental involvement in his report on children's myoelectric fittings (13). We have found parental and family support to be an important issue affecting our treatment program's success as well.

Every effort should be made to maintain effective, open lines of communication with the parents as well as to design the treatment delivery system in such a way that even the most common stumbling blocks have been removed. For instance, there should be flexibility in scheduling appointments. O&P practitioners should try to identify potential problems as early as possible and work to resolve them.

Advantages and Disadvantages

Inevitably, the question of comparative advantages and disadvantages between the electronic prosthesis and the mechanical cable-driven prosthesis arises. Electronic limbs' greatest benefit is the more natural appearance of the electronic hand. Although an infant may have little or no appreciation for cosmetic appearance, our experience has shown that parents' acceptance of their child's prosthesis is closely related to its appearance.

Many parents have admitted that they have either delayed or indefinitely postponed previous prosthetic treatment when offered choices among hook terminal devices only. This information coincides with the early findings of Aitkin and Frantz, and Sharples' later study of more than 300 amputees, which identified cosmetic appearance as amputees' number-one priority (14, 15).

Secondly, because the electronic hand is electrically powered, it provides a grip force that more closely approximates the strength of an infant's natural hand. When compared to the one-quarter to one-half pound of pinch available on most cable-driven hooks, the four pounds of grip available with the smallest electronic hand provides a much more functional prehensor.

A third consideration is the potential ability of the prosthesis to be used in all spacial planes, compared to the limitations of the harness-controlled, cable-driven mechanical hook. In addition, the electronic prosthesis can be controlled easily by the infant. This is particularly true of the new electronic circuits that provide single-site, single-function control, whereby an infant's muscle contraction initiates hand opening and total relaxation of the musculature provides automatic closing.

Lastly, eliminating the shoulder harness provides greater comfort, less resistance to wearing the prosthesis, and as pointed out by Challenor, eliminates the need for unnatural gross body movements (16).

Among the disadvantages is cost. This problem can be overcome with a concentrated amount of time and effort to secure adequate funding. Today, most families have health insurance that covers the majority of expenses, and in cases where both parents work, there are frequently two insurance policies, which eliminates the need for any out-of-pocket expense.

A second disadvantage is the inability to use the prosthesis in certain environments, particularly in wet or sandy situations. Since children are inclined to play in sand boxes and usually develop a fascination with water, it is not surprising that these tendencies will contribute to an occasional malfunction of the electro-mechanical system. Under these circumstances, the cosmetic glove should be inspected often for cuts or holes since it provides the basic protection for the underlying components.

A third consideration is electronic devices' use of self-suspended socket designs which, in the absence of a suspension harness, facilitate the ease with which a child may remove the prosthesis at inappropriate times. This problem can be alleviated by using an elastic or neoprene suspension sleeve to help secure the prosthesis to the child.

Conclusion

Although modern-day technology has given us the means to substitute a normal human limb with an electronic surrogate, the wisdom of applying this technology to infants has yet to be sorted out. As caregivers, we are naturally inclined to provide the best we can. Our mandate now is to be as objective as possible in performing our duties while still holding on to the subjective instincts that allow us to provide high-tech treatment with a high-touch focus.

Editor's Note: This article originally appeared in "Infants and Myoelectric Prostheses," monograph #4 in the University of New Brunswick monographs series on myoelectric prostheses, edited by A.S. Muzumdar and published in January 1992. Reprinted with permission.

CARL D. BRENNER, CPO, is a prosthetist who has practiced in Detroit for the past 25 years. Mr. Brenner is director of prosthetic research at the Michigan institute for Electronic Limb Development and also serves as research prosthetist for the Variety Club Myoelectric Center. He can be reached at 17346 W. McNichols, Detroit, MI 48235; (313) 838-8556; fax (313) 838-4454.

References:

1. Stedman's Medical Dictionary. 21st ed. Baltimore, Md: Williams & Wilkins, 1966.
2. Sorbye R. Upper-extremity amputees: Swedish experiences concerning children. In: Atkins DJ, Meyer RH III, eds. Comprehensive Management of the Upper-Limb Amputee. New York: Springer-Verlag, 1989.
3. Brenner CD. Myoelectronic prostheses for infants and small children. Proceedings of the American Academy of Orthotists and Prosthetists Scientific Symposium. Tampa, Fla., February 1987.
4. Brenner CD. Comprehensive prosthetic management of the below-elbow amputee. Proceedings of the 1990 University of New Brunswick Myoelectric Controls Course and Symposium. Fredericton, New Brunswick. August 1990.
5. Brenner CD. Fitting infants and children with electronic limbs: the Detroit experience from 1981-1990. Journal of the Association of Children's Orthotic-Prosthetic Clinics 1990; 25:2.
6. Village, University of New Brunswick, Systemtechnik and Steeper components and control systems. Proceedings of the American Academy of Orthotists and Prosthetists Seminar on Current Clinical Concepts of Electrically Powered Upper-Limb Prostheses, Northwestern University Medical School, Chicago, Ill. September 1984.
7. Brenner CD. Electronic components and fitting considerations for children. Proceedings of the Seminar on Myoelectric Upper-Extremity Prosthetics, Rehabilitation Institute, Detroit Medical Center, Detroit, Mich. October 1987.
8. Wendt JD, Shaperman J. The infant with a cable-controlled hook: a study of development of prehension patterns. American Journal of Occupational Therapy 1970;24:6:393-402.
9. Erhardt RP. Developmental Hand Dysfunction. Tucson, Ariz.: Communication Skill Builders, 1982.
10. Gesell A. The First Five Years of Life. New York: Harper & Row, 1940.
11. Halverson HMM. An experimental study of prehension in infants by means of systematic cinema records. Genetic Psychology Monographs 1931 ;10:2-3: 107-284.
12. Brooks MB, Shaperman J. Infant prosthetic fitting: a study of results. American Journal of Occupational Therapy 1965 ;19:6:329-34.
13. Sorbye R. Myoelectric prosthetic fitting in young children. Clinical and Related Research May 1980;148:34-40.
14. Aitkin GUT, Frantz CH. Prostheses for the juvenile amputee. AMA American Journal of Diseases of Children 1955 ;89:137-43.
15. Sharples N. Prosthetic technology and patient use. Inquiry 1971;8:3:60-70.
16. Challenor BY. Limb deficiencies in children. In: Molar GE, ed. Pediatric Rehabilitation. Baltimore, Md.: Williams & Wilkins, 1985.