The purpose of this study of infants with myelomeningoceles was to evaluate the effect of stimulation of the distal spinal cord, proximal to the neural placode, on functioning lower-extremity muscles distal to the placode.
In 13 infants with lumbosacral myelomeningoceles, the lateral spinal cord was stimulated, with a monopolar probe, between its exit from the spinal canal and the neural placode. Responses of functional muscles in the lower extremities were monitored with a neural integrity monitor.
Stimulation of the lateral spinal cord resulted in no contraction of lower-extremity muscles in 7 of 13 infants in whom no nerves exited the cord between the spinal canal and the neural placode. In those with exiting nerves in that location, stimulation of the cord resulted in the contraction of functional muscles. Distal cordectomies at the junction between the spinal cord and the neural placode, distal to any nerve roots exiting from the cord, resulted in no loss of movement.
Monopolar stimulation of the lateral spinal cord does not seem to cause contraction of functional lower-extremity muscles unless nerve roots to the lower extremities exit the cord distal to the spinal canal but before its junction with the neural placode. Muscle contraction in cases in which nerve roots exit the spinal cord between the canal and the placode may be caused by the spread of current from the monopolar stimulator.