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Published on: August 25, 2014
Electromyographic studies on flexor hypertonia of the extremities of newborn infants
Insights
Newborn flexor hypertonia may not be muscle strength but residual from uterine position. Electromyogram (EMG) data shows reduced muscle activity during initial days, suggesting passive tone rather than active contraction.
Area of Science:
- Neonatal neurology
- Developmental pediatrics
- Clinical neurophysiology
Background:
- Neonatal hypertonia is common but its underlying mechanisms require clarification.
- Understanding early muscle tone is crucial for assessing neurological development.
Purpose of the Study:
- To investigate the nature of flexor hypertonia in newborn extremities.
- To differentiate between active muscle contraction and passive tone in neonatal hypertonia.
Main Methods:
- Neurological examination and superficial electromyogram (EMG) recordings were performed on 50 full-term infants.
- Assessments were conducted within the first 48 hours of life and after this period.
Main Results:
- EMG amplitudes in the upper arm's traction response were low during the first 48 hours, despite observed hypertonia.
- After 48 hours, EMG amplitudes increased while elbow flexion decreased, indicating a shift from hypertonia to hypotonia.
- Popliteal angle measurements and thigh EMG amplitudes also showed changes, suggesting altered muscle tone patterns post-birth-shock period.
Conclusions:
- Neonatal flexor hypertonia appears to be primarily residual tone from the intrauterine position, not indicative of true muscle strength.
- The findings suggest that the initial reduced EMG activity points to passive rather than active muscle contraction in early neonatal hypertonia.
Abstract:
In order to investigate flexor hypertonia of the extremities in newborns, a neurological examination and superficial electromyogram (EMG) recordings were carried out on 50 full-term infants both before and after the first 48 hours of life (the 'birth-shock period). EMG amplituds on the flexor side of the upper arm in the traction response were low during the first 48 hours despite flexion of the elbow (hypertonia); after the first 48 hours EMG amplitudes increased in a large percentage of the infants although elbow flexion decreased (hypotonia). This finding suggests that the frflex response to passive movement (traction) is weaker during the first two days of life than after this time. Flexor tone of the upper arm in recoil of the forearm increased during the first 48 hours in spite of low EMG amplitudes; after the first 48 hours the amplitudes increased although flexor tone of the upper arm decreased. The popliteal angle was more than 90 degrees in 27 infants and less than 90 degrees in 23 infants during the first 48 hours; after this period the angle was more than 90 degrees in 11 infants and less than 90 degrees in 39 infants. EMG amplitudes on the flexor side of the thigh in most cases increased after the first 48 hours for both groups of infants, i.e. those with an angle more than 90 degrees and those with an angle less than 90 degrees. It is suggested that flexor hypertonia of the extremities in newborn infants is not a result of muscle contraction (i.e. real muscle strength) but rather is residual from the infant's position in utero.
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