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Median Sensory Nerve - Recording the thumb (antidromic)

Last updated on Wednesday, April 29 2009 by blondarb

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Origin:  C6-C7 root, upper and middle trunk and lateral cord of the brachial plexus, median nerve.

Recording Site:  Thumb

Reference Site:  Thumb

Ground:  Palm or top of hand

Stimulation Site:  Wrist

Procedure:  The recording electrode is placed on the proximal phalanx of the thumb.  The reference electrode is placed on the distal phalanx of the thumb.  A distance of 10 cm is measured from G1 to the distal wrist crease between the flexor carpi radialis and palmaris longus tendons and then extended an additional 3 cm by drawing a straight line along the course of the median nerve.  Stimulation occurs at the 13 cm wrist site. The nerve can also be stimulated at the elbow (above the elbow crease, medial to the brachial artery pulse or biceps tendon).

This study can also be performed orthodromically.  A bar electrode should be placed over the wrist site, with the recording electrode distal.  The finger electrodes should be connected to the stimulator with the former “G1” electrode acting as the cathode and the former “G2” electrode acting as the anode.

Useful for studying: Median nerve lesions, including CTS. Middle trunk and lateral cord brachial plexus lesions. Cervical radiculopathies.

Normal values *:

     Amp: >15 uV    

     Distal Latency: <3.6  mSec

     Conduction Velocity: >50 m/s 

     Temperature >32.0 C