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Median and Ulnar motor nerves- Recording the 2nd Lumbrical and interossei

Last updated on Tuesday, October 6 2009 by blondarb

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Origin:   

Median – C8-T1 roots, lower trunk and medial cord of the brachial plexus, median nerve.
Ulnar – C8-T1 roots, lower trunk and medial cord of the brachial plexus, ulnar nerve.

Recording Site:  Palm, between the 2nd and 3rd metacarpal bones.

Reference Site:  Index finger

Ground:  Top of hand

Stimulation Site:  Wrist (2 sites)

Procedure:  The recording electrode is placed in the palm in alignment with the space between the index and middle fingers, between the 2nd and 3rd metacarpal bones.  The reference electrode is placed on the proximal phalanx of the index finger.  The nerve is stimulated at two distal sites – at the median nerve wrist stimulation site, proximal to the wrist crease and between the flexor carpi radialis and palmaris longus tendons and then at the ulnar nerve wrist stimulation site, adjacent to the flexor carpi ulnaris tendon.  The nerves must be stimulated at identical distances, usually 8-10 cm.

The onset latencies should be recorded and the lumbrical response should be well defined.  Occasionally, the mixed nerve potential is seen before the median/lumbrical potential and care must be taken to record the proper latency measurement.  A latency difference of 0.6 msec or more between the median and ulnar latencies is considered abnormal.