Mapping of dermatomes of the lower extremities based on an animal model.

Previous dermatome drawings have been developed on the basis of investigations in humans and thus differ among investigators. The authors recently reported detailed dermatomes of the rat hindlimb that were mapped by electrical stimulation of spinal nerves and observation of plasma extravasation in the corresponding skin. In this paper a new human dermatome chart is proposed that has been reconstructed from rat dermatomes; the accuracy of previously reported dermatomes is also discussed. These newly defined dermatomes are arranged as serial semicircles, not as bands extending spirally from the low back down to the lower extremity as shown by Keegan. The posterior pattern differs markedly from that of any previously described charts in that the S-2 dermatome is "interposed" within the S-1 dermatome. This study clarifies the basic arrangement of lower-extremity dermatomes. Based on the present chart, it is concluded that Bonica's dermatomes are the most accurate among those previously reported.