Radial sensory innervation to index and middle fingers: electrophysiologic considerations

Antidromic radial and median compound sensory nerve action potentials (CSNAPs) were recorded from the index and middle fingers in 20 subjects. No appreciable radial sensory response can be seen at the middle finger. Seventy-five percent of subjects had radial CSNAPs at the index finger, seen to a variable extent along the finger, with 40% having a response limited only to the base of the first phalanx. Radial CSNAP amplitude was small compared to median CSNAP (ratio = 0.16). Because of the small size and wide variability among individuals, radial CSNAPs from index and middle fingers seem to have limited direct clinical utility. Contamination of median CSNAPs by radial CSNAPs is negligible or absent (when there is unavoidable spread of the stimulus to the radial nerve), if median sensory responses are recorded from the distal half of the index or middle finger.