NEUROPHYSIOLOGY OF LOWER-LIMB FUNCTION IN HEMIPLEGIC CHILDREN J. K . Brown J. Rodda E. G . Walsh G . W . Wright

We have previously reported the clinical and neurophysiological correlates with function of the upper limb in a group of hemiplegic children (Brown et al. 1987). We demonstrated that function related particularly to speed of movement and distal power, that proximal power was well preserved and that muscle tone was statistically significantly related to measurement of the resonant frequency of the muscle. Function did not appear to be directly related to the changes in muscle tone. The present study was an attempt to measure similar parameters in the lower limb. In contrast to the upper limb, fine distal manipulative movements are not required; walking is more dependent on proximal movement. It is known that all purely hemiplegic children should eventually walk independently (Crothers and Paine 1959). The deformities and problems requiring physiotherapy for the lower limb of hemiplegic children usually relate to the ankle and not to the hip. Failure to walk, scoliosis, dislocation of the hip or adductor spasticity in a hemiplegic child suggest that the child has asymmetrical diplegia, associated ataxiaas often happens following subependymal haemorrhage, with consequent posthaemorrhagic hydrocephalus-or hemiplegia following perinatal asphyxia, when the opposite side is often also affected,

though there may be marked predominance of one side (Brown 1984). Hemiplegia accounts for one-third of all cases of cerebral palsy and many of these are due to perinatal strokes, causing a strictly unilateral brain lesion (Brown 1984). These children can be expected to walk, talk, have normal urinary and faecal continence and cope with school, although they may have fits, learning disorders or behaviour problems. m p'

Patients

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The study comprised 18 hemiplegic children. The inclusion criteria were: (1) all were within the age-group from five to 15 years; (2) all had a strictly unilateral lesion on neurological examination and the hemiplegia was the only motor disability; (3) all were receiving formal schooling; and (4) all could walk unaided. Informed consent was obtained from the parents, who were present during testing. All 18 children were examined with a number of neurophysiological tests. 16 underwent more detailed testing in cooperation with the Department of Physiology, University of Edinburgh. The mean age of the group was 9 . 3 5 (range six to 14) years. There were 13 boys and five girls. 12 of the 18 children had congenital hemiplegia; the other six were postnatally acquired. 11 children had right hemiplegia (seven congenital) and

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seven had left hemiplegia (five congenital). 17 of the 18 children attended normal school. 17 of the children had normal speech and one had very mild dysarthria, with some nasal escape. Epilepsy had been a problem for five of the children in the past, but none was taking anticonvulsant medication at the time of testing.

Method

the muscles were divided at the knee into proximal and distal muscles. Proximal muscles were tested during hip flexion, extension, abduction, adduction, knee flexion and knee extension. Distal muscles were tested during dorsiflexion and plantarflexion at the ankle, together with eversion and inversion. This gave a total power score of 30 for proximal muscle power and 20 for distal muscle power.*

Clinical and neurological tests .-e

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GROWTH AND AUTONOMIC FUNCTION

REFLEXES

Growth of the leg was measured from the anterior iliac spine to the medial malleolus. Mid-calf and mid-thigh circumferences were measured to assess distal and proximal wasting. Autonomic function was assessed by colour of the foot-whether it was white, pink or showed evidence of erythrocyanosis-and by temperature differences between the foot and thigh and between feet on the affected and normal side. Capillary refill time was measured by compression of the pulp of the big toe, and trophic changes were looked for in the skin and hairiness of the limb.

Reflexes were graded according to the following system: 0 = no response; 1 = diminished response; 2 = normal reflexes; 3 =brisk reflexes (wide afferent field, low amplitude stimulus); and 4 =very brisk reflexes with clonus. Also noted was whether muscle spasm could be induced by repetitive tapping or cross-spread, and the width of the afferent field. Reflexes were charted at the ankle, knee, hamstrings and adductors.

RANGE OF JOINT MOVEMENT

Range of movement at the ankle, knee and hip was determined using a simple goniometer and the results were charted. A scoring system was employed at the ankle, with 0" corresponding to the rightangle position. Measurements were then taken in dorsiflexion, plantarflexion, eversion and inversion with the knee flexed and then with the knee extended. At the hip, extension, flexion, internal and external rotation with the knee flexed and extended were measured. Abduction and adduction ranges were measured and any fixed contracture around the joint was documented. MUSCLE POWER

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Muscle power was charted using MRC grading (Medical Research Council 1943), in which 0 = no contraction, 1 = flicker or trace of contraction, 2 = active movement with gravity eliminated, 3 =active movement against gravity, 4 = active movement against gravity and resistance and 5 = normal power. Muscle power was charted for 10 muscle groups in the lower limb;

MUSCLE TONE

Muscle tone is notoriously difficult to assess clinically and a simple clinical grading was used from hypotonia through normal tone to mild, moderate and severe increase in resistance, i.e. hypertonia. Muscle tone was tested by rapid and slow stretch. The effects of body position in a prone and supine position with the head flexed and extended were observed. This allowed us to grade the muscles as hypotonic, normal, rigid, phasically spastic or tonically spastic. This grading was used to assess eight groups of muscles: gastrocnemius, tibialis anterior, quadriceps, hamstrings, iliopsoas, glutei, hip abductors and hip adductors. The majority of the children had mild phasic spasticity. A phasic spastic 'score' was obtained from a combination of type of hypertonus, score for brisk reflexes, presence of clonus and whether spasm could be elicited by repeated stimulation. A total score of 12 was given for a muscle that showed clonus, clasp-knife resistance to rapid stretch, ease of spasm and brisk reflexes. The score for a normal muscle was 4. *Power score = maximum MRC grade x number of muscle groups.

Neurophysiological tests The second component of the examination was simple neurophysiological tests to obtain a more objective assessment for comparison with the clinical assessments. These tests were administered to all children. MUSCLE POWER

Power of plantarflexion was measured with the child lying in a lateral position, with the leg straight and the foot in neutral position, pushing against a flat board. The board was attached hydraulically to a pressure transducer, which in turn was fed through an amplification system to a pen recorder so that maximum pressure exerted could be recorded for each foot. The leg was suspended in a sling, with the knee extended and the ankle stabilised to minimise any overflow from the quadriceps and hamstrings. FATIGUABILITY

Fatiguability was measured using the same apparatus. Once maximum pressure had been measured the child was asked to sustain this until pressure dropped to 50 per cent below maximum; this was used as the cut-off point. The ability to hold maximum power for more than 100 seconds was considered normal. MAXIMUM MOVEMENT

SPEED

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VOLUNTARY

A simple accelerometer was connected to the child’s big toe with micropore strapping. The child was asked to wiggle the toes as quickly as possible for 15 seconds and the maximum speed achieved was taken. The amplitude of the trace usually was greater for the non-hemiplegic side, but we did not attempt to use amplitude as part of the measurement. Proximal joints were stabilised as far as possible. REACTION TIME

Reaction time to an auditory stimulus was assessed, using a simple foot-switch connected to a randomised auditory stimulator which measures time taken to press a foot pedal after hearing an auditory stimulus. After a number of trial runs-as practise tended to reduce reaction timethe fastest of three stimulations was taken

for each side. In addition to the auditory stimulus, a visual reaction time to the appearance of a light was also measured, but was not found to give any helpful additional information.

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CLINICAL MOBILITY SCORE

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To assess hand function we had used a grading of various hand skills. We attempted to use stepping in the same way to test posture and mobility. The child’s ability to climb a specially constructed wooden stair, using alternate feet, the ability to hop on each leg, stand on one leg, tandem walk, walk on a 7.5cm beam and crouch without support or associated movements gave a total posture and mobility score of 11. Since the youngest child in the study was six years and all the children had independent mobility, they all achieved the highest score possible. The items were chosen from previous studies of test of posture and mobility (Minns et a/. 1981). Gait analysis Gait was assessed in all 18 children according to the method described by Law and Minns (1987). This is a simple, non-invasive task: the child pulls a tape through a photo-electric device which feeds into a microcomputer, allowing assessment of self-selected and maximum walking speed, cadence as steps per minute, double support time (when both feet are in contact with the ground simultaneously during a gait cycle), stride length and velocity of swing (which indicates the maximum velocity of a movement at the hip). Specialised neurophysiological testing Sixteen of the 18 children underwent specialised neurophysiological testing at the University Department of Physiology. A torque generator motor was used to supply a series of pre-set torques through the ankle which could be applied with increasing frequency. The child’s foot was placed in a clamp (Fig. 1) which was articulated to move passively into dorsiflexion and plantarflexion. This allowed measurement of the range of movement at the ankle joint: (a) passively, with the examiner moving the ankle through the maximum range with the child relaxed;

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TABLE I

Test results

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Test Power Distal Transducer (kg) Clinical (MRC) ( m a = 20) Fatigue time (s) Speed Accelerometer (Hz) Spasticity score (normal = 4) Resonant frequency (Hz) Gait analysis Walking speed (m/s) Cadence (steps/min) Double support time (s) Swing velocity (mh) Total mobility score (max = 1 1) Reaction times (ms)

N

Normal leg Mean (SO)

Hemiplegic leg Mean (SO)

16 18 14

26.00 20.00 60.14

(7.469) (38.50)

18.937 15.000 89.64

(5.831) (1.947) (24.80)

0-01 0.01 0.01

18 18 15

53-50 8.5 5.1

(0.96) (2-17) (0-590)

17.50 4.05 4.6

(0.89) (0-802) (0.498)

0.01 0.01 0.1

18 18 17 18 17

0.1771 2.973

1.50 100.27 (0.066) (0.67) 7.1765

(1.45) (15.32) 0.221 3-046 (2.5307)

(0.077) (0.66)

0.01 0.01

16

399

(1.53)

0.01

(0)

(143)

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.&, Fig. 1. Clamp holding child’s foot in position for measurement of resonant frequency at ankle joint.

(b) actively, with the child attempting maximum plantar and dorsiflexion; and (c) of the result of set forces externally applied by the torque generator motor. It was also possible to measure the maximum speed of voluntary movement at the ankle in a way similar to that used for speed of movement of the toes: with the accelerometer, using the torque generator motor sensors to record the maximum speed of voluntary dorsiflexion and plantarflexion. The resonant frequency is the frequency at which the most rapid speed and distance of excursion occurs for a given force (Walsh and Wright 1987). ELECTROMYOGRAPHY Electromyography (EMG),

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using surface electrodes applied by means of suction caps, was used over the origin of the

plantarflexors and dorsiflexors of the foot. We were able to assess whether there was electrical silence in response to passive plantar and dorsiflexion, both by the examiner and by the torque generator motor; and, if there was electrical activity on stretch, whether this was a phasic or tonic response. EMG activity at rest was also evaluated uising movements of the head or stimulation over the mid-face, to show whether there was still a dystonic element and also whether there was co-contraction of agonist and antagonist muscles. Normal muscle at rest should have complete electrical silence during passive stretch of the calf and dorsiflexors (lengthening and shortening reactions). To ascertain whether the child was relaxed, we measured EMG activity during passive movement of the normal leg: voluntary stiffening usually caused cocontraction, with EMG activity in flexors and extensors.

Results Muscle power Distal power was significantly weaker in the hemiplegic than in the normal leg @

Neurophysiology of lower-limb function in hemiplegic children.

Equinus in hemiplegic children is multifactorial. In some cases it is due to a short muscle, in others to simple foot-drop, tonic spasticity, rigidity...
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