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.