G1 active recording electrode
G1: extensor pollicis longus tendon
Place G1 in the anatomical snuffbox on the dorsolateral wrist, directly over the superficial radial nerve as it crosses the thumb extensor tendons.
Table 2 · p.373 ↗
Sensory study
Upper limb
Superficial radial sensory nerve conduction study
Record over the extensor pollicis longus tendon near the anatomical snuffbox and stimulate proximally along the radius.
01 · Placement
G1, G2, stimulation and ground landmarks
G2 reference electrode
G2: base of the thumb
Place G2 on the dorsal thumb 3–4 cm distal to G1, continuing along the same line over the thumb extensor tendons.
Distance · 3–4 cm distal to G1
Superficial radial sensory technique · p.19 ↗Stimulation site
Stimulation: along the radius
Stimulate over the distal mid-radius, 10 cm proximal to G1 along the radial border of the forearm; orient the cathode toward G1.
Distance · 10 cm proximal to G1
Table 2 · p.373 ↗Ground region
Ground electrode region
Place the ground on the dorsal radial wrist or distal forearm between S1 and G1, clear of the recording electrodes.
Table 2 · p.373 ↗02 · Reference values
Adult normal limits
| Measure | Reference limit | Basis |
|---|---|---|
| SNAP onset-to-peak | ≥7 µV | 3rd percentile lower limit |
| SNAP peak-to-peak | ≥11 µV | 3rd percentile lower limit |
| Onset latency | ≤2.2 ms | 97th percentile upper limit |
| Peak latency | ≤2.8 ms | 97th percentile upper limit |
| Conduction velocity | ≥50 m/s | Published 3rd percentile |
03 · Technique
Acquisition conditions
Fixed distance
G1 to stimulation site: 10 cm
Sensitivity
5–10 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 superficial radial sensory reference values.