There are two kinds of techniques in placement of stimulating and recording electrodes for the determination of distal latency of peripheral nerve; one method using anatomical landmark, the other utilizing premeasured distance between two electrodes.
The purpose of this study was to determine normal values of the distal latency of the median and ulnar nerve performing by two methods, and was find out their correlations.
Seventy sixx healthy adults, 39 males and 40 females were examined. Distal latency and active potential amplitude of the median and ulnar nerve of both hands were. performed twice according to two techniques in all subjects. In first exam (Anatomical Landmark Group) : Stimulating surface electrodes were placed to the proximal wrist crease across the lateral border of the palmaris longus tendon for the median nerve, and was placed at the proximal wrist crease across the lateral border of the floxor carpi ulnaris tendon for the ulnar nerve.
Recording electrodes were placed over the thenar eminence at midpoint of the line which is drawn between the stimulating site and the midportion of the flexor crease of metacarpophalangeal joint of the thumb for the median motor distal latency, and were placed over the hypothenar eminene one half way between stmiulating site and the distal-palmar crease across the ulnar border of the hand for the ulnar motor distal latency. For the distal sensory latency, surface ring electrodes were placed at the proximal interphalangeal joint of the index finger for the median nerve and little finger for the ulnar nerve.
In second exam (Premeasured Group) : Recording, reference ..nd ground electrodes were placed at the same site of anatomical landmark group. However, stimulating electrode was placed at the lateral border of the palmaris longus tendon, 7 cm proximal to recording electrode for median distal motor and 14cm for sensory latency, respectively. For the ulnar distal motor and sensory latency, placing stimulating electrodes also 7 cm and 14 cm proximal to recording electrode at the lateral border of the flexor carpi ulnaris tendon, respectively.
The results were as follows:
1) In anatomical landmak group, the distances between the stimulating and recording
electrodes for the median and ulnar distal motor latency were 5.36±0.64 cm, and 5.2240.63 cm, respectively and 13.38±1.19 cm, and 11.59±1.23 cm for median and ulnar distal sensory latency, respectively. .
2) In anatomical landmak group, the mean values of median and ulnar distal motor were 2.86±0.27 msec and 2.39±0.28 msec, respectively and 2.98±0.30 msec and 2.73±0.28 msec, for median and ulnar distal sensory latency, respectively.
3) In premeasured group, the mean values of median and ulnar distal motor latency were 3.19±0.27 msec, and 2.67±0.24 msec, respectively, and 3.10±0.23 msec, and 3.12±0.23 msec for median and ulnar distal sensory latency, respectively.
4) In premeasured group, the mean differences of distal motor and sensory latency between the median and ulnar nerves were 0.47±0.30 msec and 0.26±0.21 msec, respectively.
5) The mean values of median and ulnar distal motor and sensory latency in anatomical landmark group were shorter than those in premeasured group.
6) There were no significant differences of median and ulnar distal latency between sex and age, and no remarkable differences of action potential amplitude between median and ulnar nerve were observed.
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