G1 active recording electrode
G1: EIP muscle belly
With the forearm pronated, place G1 over the extensor indicis proprius belly approximately two fingerbreadths proximal to the ulnar styloid.
Radial motor study · p.18 ↗
Motor study
Upper limb
Radial motor to extensor indicis proprius nerve conduction study
Record over EIP and stimulate at the forearm, elbow, below the spiral groove and above the spiral groove.
01 · Placement
G1, G2, stimulation and ground landmarks
G2 reference electrode
G2: ulnar styloid over the EIP tendon
Place G2 over the ulnar styloid on the distal extensor indicis tendon, at least 3 cm distal to G1 and completely off the muscle belly.
Distance · At least 3 cm distal to G1
Radial motor technique · p.19 ↗Stimulation site
Forearm stimulation: over the ulna
Stimulate over the dorsal ulna 4–6 cm proximal to G1 with the cathode directed toward the recording electrode.
Distance · 4–6 cm proximal to G1
Radial motor study · p.18 ↗Stimulation site
Elbow stimulation: between biceps and brachioradialis
Stimulate the radial nerve at the lateral elbow in the groove between the distal biceps tendon and brachioradialis.
Distance · Variable—measure the S1–S2 segment on the patient
Radial motor study · p.18 ↗Stimulation site
Below spiral groove: lateral mid-arm
Stimulate at the lateral mid-arm between biceps and triceps, immediately distal to the radial nerve's spiral-groove segment.
Distance · Variable—measure the S2–S3 segment on the patient
Radial motor study · p.18 ↗Stimulation site
Above spiral groove: proximal posterior humerus
Stimulate over the proximal posterior humerus near the axilla, proximal to the spiral groove; measure this segment directly on the patient.
Distance · Variable—measure the S3–S4 segment on the patient
Radial motor study · p.18 ↗Ground region
Ground electrode region
Place the ground on the dorsal forearm between the distal forearm stimulation site and the EIP recording electrodes.
Table 2 · p.373 ↗02 · Reference values
Adult normal limits
| Measure | Reference limit | Basis |
|---|---|---|
| Distal CMAP amplitude | ≥2 mV | AANEM educational reference |
| Conduction velocity | ≥49 m/s | Method-matched segment |
| Distal motor latency | ≤2.9 ms | 4–6 cm distal distance |
03 · Technique
Acquisition conditions
Fixed distance
G1 to distal forearm stimulation: 4–6 cm; measure every proximal segment on the patient
Sensitivity
5 mV/div
Sweep
2 ms/div
Limb position
Hand pronated; confirm a negative CMAP onset at EIP
Filter
2–3 Hz–10 kHz
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
Radial motor reference values recorded from extensor indicis with a 4–6 cm distal segment.