Evaluation of a myoelectric hand prosthesis for children with a below-elbow absence
M. A. Mendez *
Abstract
A clinical evaluation of a myoelectric hand prosthesis was carried out within a multicentre trial in three centres in the United Kingdom. The aim was to assess its effectiveness as an acceptable device for young children and to evaluate its technical efficiency. The trial ran for 2% years and included 87 children. The methodology used and the results obtained are presented with indications towards future developments.
Introduction
Myoelectric systems for adult arm amputees have been available and fitted in the United Kingdom, without much success, for many years. It was not until 1971 that Sorbye in Sweden started to promote the fitting of these devices to very young children (Sorbye, 1977). By 1977 the development was beginning to arouse interest overseas, with much media publicity in the U.K. In view of this in April 1978 the Department of Health and Social Security (DHSS) decided to assess the value of such prostheses and to mount a trial, on a national basis, in three centres, namely Roehampton, Manchester and Edinburgh.
The objectives of the trial were to evaluate the technical efficiency of the hardware and assess its functional ability and acceptance rate when fitted to young children.
It was agreed that a common policy regarding the selection of children, assessment, fitting and training methods should be established and by August 1978 these had been agreed.
As all children who fufilled the criteria for selection were eligible for inclusion a comparative study or random selection would have been unacceptable to parents and made the sample too small for valid results. Equally it was recognised that at the end of the project certain findings would be quantifiable by scientific methods and others would be the subjective views of experts in the field, supported by the views of the parents involved in the trial. Eventually the trial ran for two and three-quarter years-and was divided into three phases determined by the ages of the children eligible in each concurrent year.
Selection of children
Following the experiences in Sweden the criteria for selection of children were:
Age range: 3 1/2 - 4 1/2 years
A single below-elbow-amputation optimum length 5cm-12cm
A previous conventional prosthetic wearer
Cooperative and responsible parents
Children who fulfilled the selection criteria were seen for assessment at the appropriate centre by a doctor, occupational therapist and social worker and final selection was made. A myotester was used to determine response signals in the stump. An acceptable level was above 5 micro volts.
Table 1 shows the total number of children selected for each centre with the trial divided into three phases.
Prescription and prosthetic fitting
Having been selected each child, accompanied by a parent, attended the chosen centre for measurement and a cast to be taken. The socket was made and one week later the child returned for a fitting. If this was satisfactory delivery and training was initiated a week later.
Hardware
The prosthesis has a supracondylar socket with mounting points for a pair of electrodes/ amplifiers (Fig. 1, left). The latter have digital readings and can be set for flexion and extension sensitivity, a particularly useful adjustment during initial training. The prosthesis is provided with a passive friction wrist movement which allows the hand to rotate through 360°. An external 6 volt battery is worn connected by a cable to the prosthesis (Fig. 1, right).
Training programme
The training was carried out by occupational therapists experienced in Arm Training techniques. The mother and child attended for one week's intensive training and follow-up occurred at four and eight weeks, and thereafter at approximately three monthly intervals.
Initial training week
The initial training week involved delivery of the limb by the prosthetist and a structured training programme devised by the occupational therapist for the child and mother ending with a clinical review by the doctor. A comprehensive report was then written recording electrode sensitivity settings, Task Performance Test results and the child's and mother's acceptance levels and attitudes.
The child's programme included formal play activities which concentrated on manipulative skills. Free play was both individual and with groups of other children. Finally a Task Performance Test was carried out.
The mother was involved throughout as a co-therapist in practical aspects of putting the limb on, coping with battery changing, counselling in the use of appropriate activities to encourage the child to use the hand and in coping with the emotional pressures engendered by the trial. She was given a record sheet on which to note a daily diary of usage for the next 28 days.
Follow-up training
Follow-up training involved a one day visit to review the prosthesis, discuss with parents the diary of events recorded by them, observation in free play activity, further structured activities and another Task Performance Test.
Clinical evaluation
Clinical evaluation was concerned with skin reaction to wearing a close fitting socket, the Task Performance Test, interchange with conventional prosthesis and parents' expectations and reporting.
Task performance test
The Task Performance Test was devised by the occupational therapists based on experience with conventional limb users in the same age group. Its aim was to produce a competence baseline for each child which was scored and recorded. It was not used as a comparative test between different children. Structured activities covered in the training programme were used. Six activities were scored on successful achievement within a given time. A puzzle was scored on the time it took to take out and replace the pieces. Parents found the numerical results a useful yardstick on which to plot their child's progress.
Table 2 shows the scoring with a trend for progressive improvement on structured testing over a three month period. No test can identify spontaneous use in free play and the occupational therapists had to use observation techniques and parental reporting to assess this.
Conventional prosthesis
Each child was issued with a conventional prosthesis and parents were asked to keep it readily accessible for the child to make a free choice as to which prosthesis they used. Some interchanged frequently and 24%, at the time of reporting, still do.
Parents' expectations
From the onset it was recognised that parental attitudes, needs and expectations were vital factors in the evaluation process as no 3 1/2 year old makes independent decisions and parental influence is strong. Once all the children had been trained initially, a questionnaire with rating scores was sent to all parents, accepting that their comments would be based on differing periods of experience. A 95% response rate was received. The subjects covered in the parents' questionnaire are listed below.
Time worn
Child's acceptance of hand
Child's use of hand
Interchange with conventional prosthesis
Previous prosthetic achievement
Reliability
Fulfillment of expectations
Technical evaluation
For the technical evaluation, records were kept on computer of breakdown rates and their causes. Additionally an event counter was fitted into the hand to record closing impulses. This was mainly a tool to assess durability but dramatic changes in counts during training and follow-up did alert the occupational therapists to changed use and function.
Major causes of breakdown can be seen in Table 3, with glove wear and tear remaining throughout the major problem.
The time factor between breakdowns was reduced with design change following experience in Phase I from 20 days to 60 days on all repairs and 40 days to 120 days in hand repairs.
Results
The results evaluated from the project were as follows. The rejection rate was 20% (18 children). The reasons are difficult to define except in a few cases. Another 20% wore the arm either intermittently-mainly cosmetically-or for minimal functional use; 60% wore it continuously, used it effectively and derived benefit from it. In 75% of cases, parents' expectations were fulfilled-a significant factor as they found the package of cosmesis coupled with function an advantage; 84% of parents felt the breakdown rates had been at an acceptable level; 26% gave unsolicited comment that their child had gained psychologically.
With these results the DHSS decided to accept the myoelectric prosthesis for young children and it has now been available through the normal NHS Limb Fitting Service since September 1981 using basically the same clinical assessment criteria as for the trial.
Conclusion
The trial (DHSS, 1981) showed that children with a below-elbow absence who are between the ages of 3 1/2 to 4 1/2 years can be fitted successfully with a myoelectric prosthesis over the short term. Longer term results are still being evaluated. Indications are that as the children on the trial move on to the larger U.K. hands, which have quicker opening and closing responses, there are no further signs of rejection.
A research and development programme ran parallel with the trial and has made the range of hardware for upper limb amputees in the U.K. more extensive. Myoelectric hands are now being used in a variety of systems for other levels of amputation using different control strategies.
References:
- Department of Health and Social Security (1981). Report on the trial of the Swedish myoelectric hand for young children-London: DHSS
- Sorbye, R. (1977). Myoelectric controlled hand prosthesis in children. Int. J. Rehabil. Res. 1,15-25.
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