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.

Nerve conduction studies show no exclusive ulnar or median innervation of the ring finger.

In 2047 hands of 1260 patients referred for an analysis of their brachialgia, distal antidromic sensory conduction was investigated in the median and ulnar nerves. No median sensory nerve action potentials (SNAPs) were obtained from the ring finger (D4) in 257 hands, while ulnar D4 SNAPs were lacking in 38 hands. An obvious lesion of the relevant nerve could be demonstrated in each of these cases. In all remaining cases, in which D4 SNAPs were obtained with both median and ulnar stimulation, it could be excluded that they were due to co-stimulation. These findings are not in agreement with the occurrence of mononeural innervation of D4 as a physiological variation, which has been reported in some clinical and experimental studies. Comparison of SNAP parameters in 183 hands with increased median nerve distal latencies showed conduction to be more impaired in the fibers innervating D4 than in those supplying D3.

The lateral femoral cutaneous nerve: nerve conduction technique.

In 58 subjects without signs or symptoms of peripheral nerve disorders, an antidromic sensory nerve conduction study was performed on the lateral femoral cutaneous nerve. Anatomic dissections were performed on two cadavers to reveal the course of the nerve and to localize the optimal stimulation and recording sites. Mean sensory nerve action potential latency was measured at 1.7 msec (SD = 0.23) with a mean amplitude of 10.5 microV (SD = 4.0). The optimal localization of recording and stimulating surface electrodes and nerve conduction technique procedures are discussed. Reliable electrophysiologic criteria, according to age and body mass index, are obtained.