Bilaterally Controlled Neuromuscular Activity in Congenitally Malformed Children- An Electromyographic Study

Herbert W. Ladd Therese G. Simard


This study was supported by the Medical Research Council of Canada.

The neuromuscular development of the anatomically healthy child is part of his general development and is dependent, in part, on the interoceptive and proprioceptive reciprocal feedback between muscles and muscle segments5. It has been shown that both anatomically healthy children and thalidomide children were able to consciously control their neuromuscular activity3,4. The ability to exercise conscious control of single-motor unit activity, inhibition and other levels of neuromuscular activity in the muscles of the shoulder girdle was demonstrated by both of these groups, but to a much lesser degree in the thalidomide children. In these studies the neuromuscular activity was measured by the intramuscular electromyographic technique.

The research now being reported was based on the procedures developed in these two studies. It dealt with the extent and precision with which children with congenitally malformed upper limbs could consciously control the neuromuscular activity of both shoulder girdles. The possible long-range application of such research is the use of controlled neuromuscular activity to activate prosthetic and orthotic devices.

Subjects

Two different populations of upper-limb malformed children were available. In one sample the etiology of the malformation was due to thalidomide; and in the other sample it was unknown. The thalidomide sample involved seven subjects with a mean age of nine years; and the unknown-origin sample had 12 children with a mean age of nine plus. The rhomboid major muscle was selected for study in determining ability to control the neuromuscular activity of the shoulder girdle since this muscle was not generally deformed anatomically in the thalidomide children. The varying degrees of malformation for the two samples are shown in Fig. 1 .

In the thalidomide sample six of the seven children were involved bilaterally and one unilaterally. In the unknown-origin sample, two were involved bilaterally and ten unilaterally.

Experimental Equipment

The apparatus used consisted of a shielded, grounded subject room (6 ft. by 9 ft.), an eight-channel Honeywell ultraviolet polygraph, a four-channel oscilloscope (Tektronix type), an FM magnetic tape recorder (Sanborn type), and a ten-inch loudspeaker with amplifier. The oscilloscope was used for the visual feedback of neuromuscular activity to both the subject and the experimenters. The speaker system provided auditory feedback of the biological activity. This feedback system facilitated the learning procedure.

A bipolar intramuscular wire electrode was introduced into the two rhomboid muscles through a hypodermic needle (No. 27). This type of electrode has been described in detail elsewhere1. An additional surface electrode was positioned adjacent to one of the intramuscular electrodes for grounding purposes.

Procedure

Pre-training

The objectives of the research and the general procedures to be followed were first discussed with the child. The child was then seated comfortably at a small table about three feet from the oscilloscope. Next he was asked to fold his arms on the table and put his head down on them. The installation sites in the rhomboid were located by anatomical landmarks4. The sites were halfway between the spinal border of each scapula and the spinous process of the fourth dorsal vertebra and 1.25 cm. into the muscles.

The bipolar electrodes were then connected to the pre-amplifier by a special spring-clip lead4. The pre-amplifiers fed the oscilloscope and the auditory feedback system as well as the polygraph.

Once the electrodes were both installed and connected, the child was asked to lift his shoulder, push it backwards and return it to the resting position. This allowed the child to view and hear his own neuromuscular activity, and its absence, as well as to relate the visual and auditory feedback to his own shoulder movements. This procedure was done independently for each of the two muscles.

Training

The training for control over the neuromuscular activity of the two rhomboid muscles was conceptualized in three phases: 1) individual controls; 2) simultaneous control; and 3) consecutive simultaneous control.

In the first phase the ability to control the neuromuscular activity through shoulder movement at the levels of inhibition, moderate activity, light activity, and single-motor unit activity was determined in each of the two rhomboids taken one at a time. The child was asked to maintain each achieved level of control for approximately two minutes. Both the visual and the auditory signals of the neuromuscular activity were fed back during this phase.

In the second phase the goal was to determine whether neuromuscular activity could be simultaneously controlled in the two muscles at the same levels of control as were achieved with either one or both muscles in the first phase (Fig. 2 ). If the child was not capable of establishing any control over the neuromuscular activity in either one or both muscles in phase one, he was not asked to participate in phase two. The child was again required to maintain each simultaneous control for approximately two minutes. In phase two only the visual signals associated with the neuromuscular activity were fed back to the child.

If, at the completion of phase two, the child was capable of simultaneously controlling the neuromuscular activity of both muscles at two or more of the four different levels of control, he was then asked to participate in the third phase. In phase three the child was asked to consecutively evoke the two or more levels of control achieved in phase two, e.g., inhibition in both muscles, single-motor unit activity in both muscles, and continue the evocation of this consecutive control. Again, only visual signals were fed back.

Results

In general the majority of the children in both samples were able to establish at least either one or more of the four levels of control over their neuromuscular activity five of the seven thalidomide children and ten of the twelve unknown-origin children. In phase one a greater percentage of the children in the unknown-origin group achieved each of the four different levels of control (inhibition, moderate, light and single-motor unit activity); and they showed greater precision in their control as 75 per cent were able to control single-motor unit activity in contrast to 30 per cent for the thalidomide group. Using Chi square analysis, these differences were found to be statistically significant at the .01 level of confidence. The results of this analysis are presented in the table which follows. While more of the subjects in the unknown-origin group achieved simultaneous and consecutive simultaneous controls in phases two and three, the differences were not significant.

Table

In the five thalidomide children who could establish one or more levels of control in phase one, it was observed that the site of best control was bilaterally equal in four of the five. In the ten unknown-origin children the site of best control was bilaterally equal in only four of the cases; in six, one side was superior to the other. An example of this unilateral control is shown in Fig. 3 . The difficulty in achieving controlled inhibition in the muscles of the malformed side should be emphasized. This difficulty was noted in several of the unilaterally malformed children.

Discussion

The results of this study indicate that children whose upper limbs are con-genitally malformed can exercise conscious control over neuromuscular activity of the shoulder girdle. However, the extent of malformation of the upper extremities plays an important role in the control of the neuromuscular activity. This conclusion is substantiated by the fact that ten of the twelve children in the sample where the origin of the malformation was unknown were unilaterally involved only, and significantly more of them were able to establish the four required levels of neuromuscular control in phase one of the training procedure than was the case with the thalidomide children where six of seven were bilaterally involved. The percentage of subjects in the unknown-origin group achieving both simultaneous neuromuscular control in the two rhomboids and consecutive simultaneous control was greater than it was in the thalidomide group, but not significantly so. Two explanations may be advanced for these differences: 1) the anatomical defects in the upper extremities and shoulder girdles of the thalidomide children were generally more inclusive than those observed in the children where the cause of malformation was unknown, with a consequent greater loss of potential to control the neuromuscular activity; and 2) the neuromuscular activity per se of the affected muscles and/or muscle segments in the thalidomide child may be more impaired than in the other cases with a resulting decrement in both the ability to control neuromuscular activity and the precision with which it could be controlled2.

The need for visual feedback in the initial training and its effect is demonstrated in Fig. 4 . The lack of either controlled activity or inhibition in the muscle(s) whose neuromuscular response is not fed back to the subject is evident. This finding confirms clearly the previously advanced theory that audiovisual feedback facilitates the acquisition of conscious control of fine neuromuscular activity.

The psychological and social problems that these children endure may affect their performance as well. In a previous study3 it was observed that they did not have the same level of interest and motivation as normal children in performing the same experimental task.

Subsequent research employing other muscles of the shoulder girdle is indicated.

Summary

The ability to control neuromuscular activity bilaterally at various levels was studied by electromyography and audiovisual feedback in the rhomboid major muscles of two groups of children with congenitally malformed upper limbs. In one group the etiology of the malformation was thalidomide; in the second group it was unknown. Levels of neuromuscular control were studied, first on each side independently, then on both sides simultaneously, and finally in the consecutive evocation of the simultaneous controls. A greater number of children in the second group achieved the required neuromuscular controls than did those of the first group. They demonstrated also a greater capacity to establish both simultaneous and consecutive controls. The results are discussed in terms of the importance of anatomically sound upper limbs for the neuromuscular control of the shoulder girdle, possible effects of thalidomide on the neuromuscular activity of the involved muscles, and psychological and social factors.

Herbert Ladd is Assistant Professor, Dept. of Psychology, Loyola College of Montreal; and Research Associate, Dept. of Research, Rehabilitation Institute of Montreal, Montreal, Quebec, Canada.

Therese Simard is Associate Professor, Dept. of Anatomy, University of Montreal; and Senior Research Associate, Dept. of Research, Rehabilitation Institute of Montreal.

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