Electrophysiological assessment of maturation of regenerating motor nerve fibres in infants with brachial plexus palsy.

Age-related changes ('maturation') of the distal latency (L) and conduction velocity (CV) along the axilla-to-wrist segment have been analysed in the regenerating median and ulnar nerves of 24 children with brachial plexus palsy and have been compared with developmental changes in healthy nerves. Results show that maturation of L and CV is more rapid after regeneration than during normal development. Up to three years of age, when L and CV in regenerating nerves reached their maximum maturity, CV values were within normal limits for both nerves in about half of the cases, indicating good regeneration ability in newborns. No specific differences were found between L and CV in the time taken to reach full maturation in the same and in different regenerating nerves, which is contrary to normally developing nerves. The results also demonstrate that the maturation process of regenerating nerves does not lead to the attainment of different specific L values characteristic of normally developing median and ulnar nerves, but to uniform non-specific values close to the mean between them. This was explained by the lack of specific afferent inflow to developing motor neurons (the result of a sensory fibre lesion), which causes the non-specific development of motor units.