The Journal of Bone and Joint Surgery, Vol 70, Issue 6 911-918, Copyright © 1988 by Journal of Bone and Joint Surgery, Inc
Monitoring of motor action potentials after stimulation of the spinal cord
M Machida, SL Weinstein, T Yamada, J Kimura, T Itagaki and T Usui
Department of Orthopaedic Surgery, Nihon University School of Medicine, Tokyo, Japan.
We recorded motor action potentials in cats, using surface electrodes
placed over the soleus muscle. The action potentials were generated by
stimulating the spinal cord with electrodes in the epidural space at the
level of the fifth or sixth thoracic vertebra. This also was done in
humans, using the same methods of stimulating and recording, but the
intensity of the stimulus was adjusted to produce little or no twitch of
the paraspinal muscles. In the animal experiment, the motor action
potential was abolished after transection of the pyramidal tract and was
progressively attenuated with effective doses of a curare-like agent. We
also tested the effect of distraction, using the same technique as is used
in Harrington instrumentation, and found that the amount of distraction
that caused reduction of the amplitude of the motor action potential of
more than 50 per cent, when sustained for longer than seven minutes, caused
permanent paraplegia in two cats. The evaluation of spinal evoked
potentials that were obtained from epidural electrodes placed caudad to the
level of distraction, and of motor action potentials that were recorded
over the soleus muscle, following the same stimulus, showed a similar
pattern of reduction after distraction in five of seven cats. The other two
cats had irreversible reduction of motor action potential associated with
unchanged spinal evoked potential, and both cats became
paraplegic.(ABSTRACT TRUNCATED AT 250 WORDS)
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