Nerve Action Potential Recording

Published on 08/03/2015 by admin

Filed under Neurosurgery

Last modified 08/03/2015

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Chapter 23 Nerve Action Potential Recording

Assessing Distal Motor Function

After external neurolysis, the next logical step in evaluation of any lesion in continuity is to stimulate the nerve both above and below the lesion, to determine whether there is any motor function distal to the lesion.

If there is muscle contraction, then enough axons have grown to the muscle in question to provide voluntary contraction, even though the patient may not be able to do it voluntarily at the time of the stimulation.

If stimulation above gives no muscular contraction distal to the lesion but stimulation below does, there is clearly an element of neurapraxic block involved.

If a few months have passed since the injury and there is no response, then the lesion is predominantly neurotmetic.

Alternatively, if the lesion is axonotmetic, either it is too far proximal to meaningful distal muscles to expect adequate regeneration, or it is too early to expect excellent regeneration to have reached them.

When using stimulation alone, care must be taken not to mistake contraction of muscles proximal to the lesion for distal contractions. One also has to be certain that the current does not spread to adjacent and often more intact muscles or nerves. The muscles seen to contract must be in the distribution of the injured nerve.

If one records as well as stimulates, the presence or absence of adequate regeneration can be detected relatively early after injury. Nevertheless, several months must elapse for even nerve action potential (NAP) recording to be useful. Thus, after external neurolysis and before internal neurolysis or repair (split or otherwise), we attempt to record NAPs.