G1 active recording electrode
G1: index finger
Place the active ring electrode around the proximal phalanx of digit II, just distal to the index-finger MCP joint.
Table 2 · p.373 ↗
Sensory study
Upper limb
Median sensory nerve conduction study
Place G1 on the index finger; stimulate at the wrist between the flexor carpi radialis and palmaris longus tendons.
01 · Placement
G1, G2, stimulation and ground landmarks
G2 reference electrode
G2: 4 cm distal to G1
Place the reference ring electrode 4 cm distal to G1 along digit II, toward the fingertip.
Distance · 4 cm distal to G1
Table 2 · p.373 ↗Stimulation site
Wrist stimulation: between FCR and PL tendons
Stimulate on the volar wrist 14 cm proximal to G1, centered between the flexor carpi radialis and palmaris longus tendons; orient the cathode distally.
Distance · 14 cm from G1
Table 2 · p.373 ↗Stimulation site
Palm stimulation: midpoint between wrist site and G1
Stimulate in the palm at the thenar crease and second metacarpal interspace, midway between the wrist site and G1, 7 cm from G1.
Distance · 7 cm from G1
Table 2 · p.373 ↗Ground region
Ground electrode region
Place the ground on the dorsum of the hand or palmar wrist between the stimulating and recording electrodes.
Table 2 · p.373 ↗02 · Reference values
Adult normal limits
| Measure | Reference limit | Basis |
|---|---|---|
| Wrist SNAP onset-to-peak | ≥11 µV | 3rd percentile lower limit |
| Wrist SNAP peak-to-peak | ≥13 µV | 3rd percentile lower limit |
| Wrist onset latency | ≤3.3 ms | 97th percentile upper limit |
| Wrist peak latency | ≤4.0 ms | 97th percentile upper limit |
| Palm onset latency | ≤1.6 ms | 7 cm segment |
| Palm peak latency | ≤2.3 ms | 7 cm segment |
| Conduction velocity | ≥43 m/s | Published 3rd percentile |
03 · Technique
Acquisition conditions
Fixed distance
Wrist to G1: 14 cm; palm to G1: 7 cm
Sensitivity
20 µV/div
Filter
20 Hz–2 kHz
Sweep
1 ms/div
Temperature
Maintain dorsal hand skin temperature >32°C
Ground
Place the ground between the stimulating and recording electrodes
Primary evidence
Method-matched AANEM reference data
Adult antidromic median sensory reference values for digit II; amplitude is also affected by age and BMI.