A Comparison of Conventional and Myoelectric Below-Elbow Prosthetic Use

FRANCIS J. TROST. MDFrancis J.Trost is a physician at the Evans and Riley Clinic, 25-15 Chicago Avenue South, Minneapolis, Minnesota 554(14).


Since 1975, forty-seven children from the Twin City Unit of the Shriners hospital have been fitted with below-elbow myoelectric prostheses.5 This study was generously funded by the Hospital's Women's Auxiliary and allowed for continuous provision of conventional prostheses while introducing myoelectric devices to the children's armamentarium. We were thus able to observe a natural selection process, unique and of critical importance to any study.

Materials and Methods

A questionnaire was sent to all forty-seven myoelectric recipients, of whom forty-five responded. The respondents consisted of twenty-six boys and nineteen girls who were fitted with below-elbow conventional prostheses between the ages of eight months and fifteen years (average age: 3.3 years). When these children's ages ranged from six to sixteen years (average age: 12.5 years) they were fitted with myoelectric prostheses. Thirty-four children wore conventional prostheses before being fitted with myoelectrics (Table 1 ). Other studies4,10 demonstrate that children as young as two years old can be fitted with myoelectric limbs. We did not, however, find this a practical age as children under ten experience a high incidence of damage to the prosthesis. Two factors support our preference for later fitting. First, as a result of the structural concessions necessary to adapt a child's hand from an adult size, the child's prosthesis is not as durable. Second, the younger child is less concerned with appearance and will not make the adjustments required to prevent breakage. Gloves, in particular, were frequently replaced. The results of our study corroborated these observations.

Although several myoelectric systems are available, the Otto Buck myoelectric prosthesis (Figures 1 , 2 ) was selected because of its suitability for the patients, its general reliability, the availability of four hand sizes (Figure 3 ) and convenient accessibility to ports and service.2

Fabrication and Repair

When the study began, in 1975, the average cost of each myoelectric unit was approximately $2000. Current inflation finds the price more than twice that. In general, the myoelectric limb is more expensive because of the additional time and labor required fur its production. The conventional below-elbow prosthesis, in comparison, costs approximately $1600. By collecting parts from those myoelectrics that have been outgrown or rejected and returned we have established a small prosthetic limb bank. Reusing components has helped control costs of the prostheses.

In this study, the number of repairs generally correlates to the amount of wear: an average of 1.9 repairs per year per patient. Repair time varied and was not quantified but, with some exceptions, did nut constitute much lost wear time. Gloves were the must common item to need repair or replacement since they are quite susceptible to soilage and damage. Batteries were the second item must commonly replaced. Other components needing frequent repair or replacement were the hand frame and thumb axis. Problems with the electrical system were uncommon, but require) longer repair time (Table 2 ).

Opinions as to the optimal length of training vary,6,8,10 but extensive additional instruction was nut necessary in our study population. Most of the children had worn conventional prostheses and knew about the operation of an artificial limb. The children were trained during the fabrication process of the prostheses and that seethed sufficient.

Results

As indicated in Table 1 , the study included thirty-four congenital amputees and eleven acquired (trauma and/or surgery) amputees. These children presented twenty-seven short below-elbow amputation limbs, four mid-length limbs, four long limbs and thirteen functional wrist disarticulation limbs. Limb length did not affect the eventual acceptance of the myoelectric prosthesis.

To classify further, the survey included three bilateral amputees who at this time consist of: one child with bilateral mid-length limbs who uses conventional prostheses and two children with bilateral wrist disarticulations who use no prostheses.

Prosthetic wear was divided into four categories based on percent of time: 0-25, 26-50, 51-75 and 76-100; the percentages were applied to the length of time that the children wore either the myoelectric, the conventional or no prosthesis.

A questionnaire was sent to the patients requesting information on comfort, function and appearance (Table 3 ).1-1 Comfort was defined by wearability and weight. Function related to speed of operation, control, utilization and energy expended. Appearance questions included psychological factors. A slight majority found the myoelectric more comfortable although most thought it heavier than a conventional limb. Patients were evenly divided as to which prosthesis was faster to operate. The myoelectric, however, was found easier to control. Again, patients were evenly split regarding utilization of the prostheses in daily activities and the amount of energy required. Appearance was heavily weighted toward the myoelectric limb.

The children were asked to list the advantages and disadvantages of the myoelectric and conventional prostheses. The must common observations are presented in Table 4 .

Overall opinion, then, favored the myoelectric limb, based on appearance and comfort, nut function. Specifically, it appears that the myoclectric prosthesis, which includes a prosthetic hand rather than a hook, has a powerful psychological impact. The nature of the unilateral limb loss suggests that the myoelectric prosthesis is useful primarily as an assist to the sound limb.

Rejections

Sixteen children, eleven boys and five girls, rejected the myoelectric prosthesis (Table 5 ). Of these, eleven are congenital amputees, five are post-traumatic.

Limb lengths included nine short below-elbow; six wrist disarticulations (including two bilateral amputees); two long below-elbow; and two mid-length below-elbow. These children were fitted conventionally when their ages ranged from eight months to eleven years (average age: 3.4 years). They were fitted myoelectrically when they were aged six to sixteen years (average: 13.2 years). These numbers generally coincide with the age at which the entire group was fitted. Currently nine wear conventional prostheses full time and seven wear none.

Overall, the children rejected myoelectric prostheses for the following reasons (listed in order of highest priority): insufficient function, fragility and heaviness. Other factors included expense, malfunction, slow operation, battery discharge, discomfort and soilage. Repair and malfunction seemed to be significant factors for only two patients. It would be informative to fit the rejecting patients, particularly the bilateral wrist disarticulation amputees, with powered hooks to see if that type of prosthesis would be more acceptable.3

Later Usage

Ten patients, six males and four females, are, at this writing, responsible for providing their own prosthetic care. Three wear myoelectric prostheses, three conventional prostheses, three wear no prostheses and one's preference is unknown. All were using myoelectric prostheses when discharged from the Shriners system. The major findings follow.

Myoelectric Prosthesis

  • Bilateral amputees do not wear myoelectric prostheses.9
  • Myoelectric limb wear was equally divided between those who wore them 25 percent of the time and 76-100 percent of the time, indicating that the number of casual cosmetic wearers equaled the number who wore the prosthesis for full functional use. One could infer, then, that the casual wearer might be tilted with a passive cosmetic prosthesis, at a savings of several thousand dollars.
  • More children wore the prosthesis over 50 percent of the time than did not.
  • Proportionally, more boys than girls rejected the myoelectrics.

No Prosthesis

  • Most below-elbow amputees wore a prosthesis functionally the majority of the time.
  • The length of the below-elbow amputation limb did not seem to relate to prosthetic acceptance, although it has been our clinical impression that wrist-disarticulation amputees frequently reject prostheses or wear them only cosmetically.
  • Unilateral below-elbow amputees occasionally go without their prostheses, particularly in the summer.

Conventional Prosthesis

  • Twice as many children wore conventional prostheses less than 50 percent of the time, as compared to those who wore them more than 50 percent of the time, indicating a shift toward myoelectric wear.

Additional Findings

  • Of the thirty-four children who wore conventional prostheses before being fitting with myoelectric limbs, seven appear to have adopted a pattern of dual functional use, wearing the myoelectric prosthesis and the conventional prosthesis equally.
  • Substantial additional training is not required.

Summary and Discussion

Forty-seven children were fitted at the Twin City Unit of the Shriners Hospital with below-elbow myoelectric prostheses since 1975. The patients were first conventionally fitted. Later, they were fitted myoelectrically and allowed to choose which, if any, prosthesis they will wear. Appreciation of function between the two prosthetic systems is subtle and requires trials using both.

Neither amputation limb length nor age of fitting is a significant factor in the acceptance of myoelectric prostheses. However, we now select children between ages nine to eleven for myoelectric fitting and ask, after providing appropriate instruction in the operation of the prostheses, for a commitment to wearing/using the limb for at least one year before deciding whether to continue its use.

Our study showed that myoelectric prostheses are a valuable, albeit expensive, adjunct in treating below-elbow amputees. However, myoelectrics are not a complete functional substitute for the conventional prosthesis.

Myoelectric prostheses with powered hands are, clearly, not suitable for bilateral amputees. Beyond this, guidelines for the selection of candidates who will choose to wear myoelectric prostheses are less. well-defined. We have found a general shift toward myoelectric limb wear and away from conventional prostheses in the unilateral amputee patient population. Of ten individuals wearing a myoelectric prosthesis at the time of their discharge approximately one-third continued in its use, one-third returned to conventional prostheses and one-third wore none.

A profound cosmetic advantage favors the myoelectric prosthesis. Patients and parents have an understandable desire to replace a missing part with one having a close resemblance to that part. However, in a situation where the child is very young and the parents are accepting and supportive of the amputee, the cosmetic advantage is not as critical.

In general, after the initial enthusiasm and a fair trial using both types of prostheses, a significant number returned to using conventional prostheses; a few to wearing none. Amputees who most depended on mechanical bimanuality, simplicity of operation and durability were the ones who returned to conventional devices. A few wore both prostheses equally but the economic feasibility of this remains in question.

For these reasons, we fit children conventionally first, adding a myoelectric prosthesis later. We will continue with this sequence until other prosthetic devices are developed.

References:

  1. Bergholtz, Susan G., Evaluation of the University of New Brunswick Myoelectric (land Control System. Prosthetics and Orthotics, New York University Post-Graduate Medical School, 1975
  2. Otto Bock Orthopedic Industry Inc., 6111 Indiana Avenue North, Minneapolis, Minnesota 55422
  3. Childress, Dudley S., and J.W. Billock, Self-Containment and Self-Suspension of Externally Powered Prostheses for the Forearm. Bull Prosthet Res 10-14:4-21, 1970.
  4. Day, H.J.B., The United Kingdom Trial of the Swedish Myoelectric Hand for Young Children: An Interim Report. Inter-Clin Inform Bull 17:5-8, 19811
  5. Jones, R.H., Cole-Chatterton Symposium. Minneapolis, Twin City, Shriners hospital, 1978. Unpublished paper
  6. Lund, Aida, Observations on a Very Young Upper Extremity Amputee. Amer J. Occup Ther 12:1522, 36, 1958
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  8. Rodgers, C.D., and R.N. Scott, Early Fitting of Congenital Amputees with Power Prostheses. Research Report 80-1: Bio-Engineering Institute, University of New Brunswick, 19811
  9. Schmeisser. Gerhard G., and William Scamone, A Five Year Review of Clinical Experience with Johns Hopkins University Externally Powered Upper-Limb Prostheses and Orthoses. Bull Prosthet Res 10-23:211-217. 1975
  10. Sorbye Rolf, Myoelectric Controlled Hand Prostheses in Children, Clinical Consultations. Second European Conference of Rehabilitation International, Brighton, England. Conference Proceedings, 1978