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Establishing Parameters Affecting the Use of Myoelectric Prostheses in Children: A Preliminary Investigation

Gary M. Berke, M.S., C.P.
Caroline C. Nielsen, Ph.D.

Abstract

Little research currently exists describing the factors that influence the use of myoelectric prostheses in children. A questionnaire was designed to evaluate the relationship between the patterns of use and function of the prosthesis and 1) length of residual limb, 2) age the child was first fit with a passive prosthesis, and 3) the age the myoelectric prosthesis was first fit. Personal interviews were conducted with the parents of 25 children between the ages of 11 months and 18 years who had been fit with a myoelectric prosthesis at a pediatric rehabilitation hospital. Results indicated that the length of the residual limb was a critical factor in continued use of the prosthesis. Results also showed that 22 percent of the below elbow amputees rejected their prosthesis completely. Suggestions for further study in related areas are discussed.

Introduction

The purpose of this study was to investigate parameters that affect the use of myoelectric upper extremity prostheses in children. In the mid-1960s myoelectric prostheses were introduced as an alternative to conventional body-powered prostheses. The conventional prosthesis is lacking in cosmetic qualities and requires extensive harnessing for function and suspension (1). Reported advantages of externally powered (myoelectric) prostheses are 1) superior pinch force of between 15 and 25 lbs. compared to 7 to 8 lbs. with a cable-operated hook, 2) improved cosmetic and social acceptance, 3) freedom from a harness and 4) improved function for high-level amputees (2).

However, little research exists describing the actual use and function of myoelectric prostheses with children. The fitting of myoelectric prostheses is currently justified on manufacturers' claims and clinical experimentation. The optimal age for fitting a child with a prosthesis has been controversial for many years. Previously, the accepted age of first fit of a myoelectric upper limb prosthesis on a child was between the ages of two-and-a-half and four years (1). Currently, between 80 and 100 myoelectric terminal devices for children under the age of three are sold in the country each year (3). Lack of documentation in the area of myoelectric fitting in children provides little guidance in determining successful candidates for myoelectric components.

In previous studies, some factors affecting the use of upper extremity prostheses have been identified, including level of amputation, age at first fitting of a passive prosthesis, and age at first fitting of a myoelectric prosthesis (4,5). The level of amputation has been considered a critical issue in the prediction of future myoelectric use (6). Unfortunately, the optimum level of amputation in elective situations, for the most effective use of a myoelectric prosthesis, has not been researched in children. Without this kind of data, the prosthetist is forced to rely on clinical experience and personal opinion.

Several studies have looked at children and the relationship between age and prosthetic acceptance. In 1983, Scotland and Galway investigated the use of conventional upper extremity prostheses in children (6). Their results showed that 50 percent of children over the age of two rejected their prosthesis, compared with only 22 percent of the patients who had been fit before the age of two. Sorbye showed that only one in 40 children over the age of 18 months rejected his prosthesis (1). Researched acceptance rates of upper extremity prostheses have varied considerably among authors and between myoelectric and conventional prostheses (2,7,8).

For this study, a chart review of the patients at a pediatric rehabilitation hospital revealed that only half of the children previously fit with a myoelectric prosthesis continue to make regular appointments for the required routine maintenance or repairs on the myoelectric prosthesis. This 50-percent return rate raised concerns because growing children require frequent socket changes, as well as occasional repairs due to prosthetic malfunction. A 50-percent return rate may indicate that only half of the children fit with myoelectric prostheses are continuing to use them. The effects of three factors were investigated: 1) level of amputation, 2) age at which a prosthesis was first fit and 3) age at which the first myoelectric prosthesis was fit.

Methods

Sample

Since congenital amputees account for only three percent of the population and upper extremity amputees make up less than 10 percent of the population, finding a significant sample size of young amputees for research purposes is difficult (9). The initial sample for this study consisted of the entire population of children at a pediatric rehabilitation hospital, under the age of 18, who had been previously fit with myoelectric prostheses (N 30). Of the 25 families contacted, 52 percent of the children were below the age of five and 56 percent of the children were male. Ninety-six percent of the children studied were amputees due to congenital malformation of one or more of their limbs (Table 1) .

Fifty-six percent of the children were below-elbow (BE) amputees, 24 percent above elbow (AE) and 20 percent were through-joint amputees. The latter group consisted of elbow disarticulation, wrist disarticulation and partial hand amputees.

Children in this facility are routinely fit at a young age with a passive prosthesis in an attempt to increase compliance by allowing the child to "get used to wearing a prosthesis." Ninety-six percent of the children investigated in this study were initially fit with the first myoelectric prosthesis under the age of two years, and 12 percent under the age of one.

An interview was carried out by telephone or in person with the parents of these 30 children. Four of the families were unavailable or refused to be interviewed. One young amputee was still wearing a temporary prosthesis and was excluded from the study because her current wear patterns would not reflect the actual use and wear. The final sample included 25 children.

Data Collection

To address the concern of prosthetic acceptance in child amputees, a questionnaire was designed to gather data on the child's prosthetic and medical history, patterns of use with the myoelectric prosthesis and pertinent parental information. The questionnaire consisted of open-ended questions, allowing parents to raise issues of concern for them, as well as questions soliciting more guided responses to provide data for comparison.

Results

As in previous studies, where patients used conventional or myoelectric prostheses, the number of hours that the prosthesis was worn was determined to be the primary indicator for prosthetic acceptance (10). The total number of hours that the prosthesis was worn at home and at school was categorized into full time, part time and none. Part-time use was defined as less than 10 percent daily wear time and use for special purposes and therapy only. A significant relationship (p<.01) was found between hours worn at school and hours worn at home, suggesting that the patients who wear their prosthesis full time at home will usually wear their prosthesis full time at school. A chi-square analysis was performed between "use" and 1) level of amputation, 2) age first fit with a passive prosthesis and 3) age when fit with a myoelectric prosthesis. Results showed a significant correlation (p<.05) between the level of amputation and use of a myoelectric prosthesis (Table 2) . In this study, 100 percent of all through-joint amputees (including partial hand, wrist disarticulation and elbow disarticulation amputees) no longer use their prosthesis. Twenty-two percent (N =4) of the BE amputees contacted rejected their prosthesis completely. The BE prosthetic acceptance rate, in this study, coincides directly with Millstein's 1982 study on adults with myoelectric prostheses (11).

Although the relationship between age at first fitting of a passive or myoelectric prosthesis and myoelectric prosthesis use was not statistically significant, the data suggest trends that should be researched further with a larger population. Over 50 percent of those fit with a passive prosthesis at less than one year of age still wear their myoelectric prosthesis full time. In comparison, less than 17 percent of those who were fit with a passive prosthesis after the age of one continue to wear their myoelectric prosthesis full time.

The age at which the myoelectric prosthesis was fit may also be associated with acceptance of the prosthesis. In this sample there are only eight children over the age of seven. However, 75 percent of those over seven years old rejected the myoelectric prosthesis. The age factor appears to be an important variable in prosthetic acceptance, but requires further study with a larger sample.

Discussion

Responses to open-ended questions provided descriptive information of value to the prosthetist. When parents were asked if there was any particular activity for which the myoelectric prosthesis MUST be worn, their responses varied considerably (Table 3) . Bicycle riding was the most frequent response, followed closely by cutting paper. While these are not usually thought of as bimanual activities, they were activities for which the children felt they needed to use their prosthesis. Stringing beads was the most popular activity used in therapy to enhance control and function of the myoelectric prosthesis. Many parents responded that there was no activity for which their child MUST wear his or her prosthesis. This report was particularly interesting, since one of the respondents was the parent of a shoulder disarticulation/short AE quadrimembral amputee, and one was the parent of a bilateral BE amputee. This suggests that upper extremity amputees, of any level, have the ability to adapt and function in the activities of daily living without the assistance of a prosthesis, either through the use of adaptive equipment or by independent adaptation. Further study should be pursued, investigating specific activities for which a myoelectric prosthesis is used.

When the parents were asked "for what reasons use of the myoelectric prosthesis might be suspended for a period of time," several responses were noteworthy. Fear of damage, while being the most common response, was the only response where the parents dictated when the prosthesis was not to be worn. Comments such as "She complained of it being very hot inside and her arm was very sweaty," or "He felt it was very heavy" were cited as reasons that children did not want to continue to wear their prosthesis. "Mood" was the most popular response among the parents of two-year-old patients (Table 4) .

There are several items that came up in the interview process and that may be important for prosthetists and require further study. Every patient who had previously worn a conventional prosthesis, but had had a time gap before the fitting of the myoelectric prosthesis, rejected both prostheses, even if the patient had been a consistent conventional wearer in the past. Although rejection may be a function of patient motivation, this finding suggests that it may be important for the prosthetist to anticipate the need for a new prosthesis and decrease the time lapse between proper-fitting prostheses.

Secondly, 88 percent of the people interviewed were the mothers of the children. Unfortunately, the mother was not always the one to answer the telephone. Fathers who were initially contacted deferred to their wives, saying "She knows more than I do about this," or "I better let you talk to my wife." One father attempted to complete the first half of the interview process prior to turning to his wife for "more accurate answers." For the healthcare professional, this information raises questions as to whether greater emphasis should be placed on incorporating both parents in the rehabilitation process. Future research may look at the role of the family in maintaining use and function of the prosthesis.

Conclusion

Several interesting trends were noted in this investigation. The length of the residual limb plays a significant role in the future acceptance of a myoelectric prosthesis. This information is essential for surgeons as well as prosthetists and appears to be an important factor affecting the acceptance and continued use of the myoelectric prosthesis. Future research with other samples of children would further substantiate this finding. In addition, continued investigation of the role of age at the final fitting and the timing of the fitting of the myoelectric prosthesis will provide further information on optimal conditions for prosthetic acceptance. With future research, it may be possible to specify parameters that predict successful use of a myoelectric prosthesis in children.

Acknowledgements

This study was completed with the generous assistance of Newington Children's Hospital, Dept. of Orthotics and Prosthetics, Newington, Conn.


Gary M. Berke, M.S., C.P., is director of prosthetics, California State University, Dominguez Hills, Calif.

Caroline C. Nielsen, Ph.D., is associate professor and director, Research and Graduate Studies, School of Allied Health Professions, 358 Mansfield Road, University of Connecticut, Storrs, Conn. 06269-2101, (203) 486-0018.

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