What is the role of needle EMG in the evaluation of common peroneal nerve entrapment?

Updated: Oct 15, 2019
  • Author: Minoo Hadjari Hollis, MD; Chief Editor: Thomas M DeBerardino, MD  more...
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Answer

Needle EMG helps in confirming axonal loss and in assessing the degree of involvement of the muscles innervated by the superficial peroneal nerve. This portion of the nerve usually is less severely involved than the deep peroneal nerve. It is possible to localize the lesion to either the deep or the superficial peroneal nerve, specifically if appropriate abnormalities are detected in the proper distribution for each nerve.

The most valuable aspect of the needle EMG examination is that it can be used to define the proximal extent of the lesion. If an amplitude drop is lacking across the fibular head but the CMAP for the anterior tibial muscle is lower than that of the unaffected side (suggesting axonal loss), it is difficult to localize the lesion to the fibular head, even though this is the most common site of peroneal nerve injuries.

In any peroneal nerve injury, regardless of the suspected site of nerve compromise, examining the short head of the biceps femoris is important. If this muscle demonstrates membrane instability (positive sharp waves and fibrillations), the lesion is proximal to the fibular head.

Testing muscles innervated by the tibial nerve, particularly the flexor digitorum longus and the posterior tibial muscle, is also important because these muscles contain predominantly L5 neural innervation from the tibial nerve. If a radicular process is present, the muscles innervated by the peroneal and tibial nerves should demonstrate membrane instability.


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