The sensory innervation pattern of the fingers.

In 32 subjects without signs or symptoms of peripheral nerve disorder, sensory nerve action potentials (SNAPs), elicited by stimulation at the wrist, were recorded from the fingers of both hands with ring electrodes. Recordings from the volar proper digital nerves confirmed the standard distribution of the median and ulnar cutaneous innervation. Recordings from the dorsal digital nerves, however, showed that the contribution of the dorsal cutaneous branch of the ulnar nerve (DCUN) strongly decreases from the little finger (always a SNAP) to the middle finger (rarely a SNAP), and that the contribution of the radial nerve decreases in an identical way from the thumb to the middle finger. Anatomical studies have shown that small branches from the DCUN and the radial nerve contribute to the innervation of the dorsal aspect of the proximal part of the middle finger, but it seems likely from our data that the predominant innervation of this area is usually provided by the median nerve. Furthermore, we found that the dorsal aspect of the proximal part of the ring finger is mainly supplied by the DCUN. These findings differ from the standard cutaneous innervation pattern as depicted in neurological textbooks, but they are in agreement with earlier anatomical studies.