EXCITATION OF DORSAL-ROOT FIBERS IN SPINAL-CORD STIMULATION - A THEORETICAL-STUDY

In epidural spinal cord stimulation it is likely that not only dorsal column fibers are activated, but that dorsal root fibers will be invol ved as well. In this investigation a volume conductor model of the spi nal cord was used and dorsal root fibers were modeled by an electrical network including fiber excitation. The effects of varying some geome trical fiber characteristics, as well as the influence of the dorsal c erebrospinal fluid layer and the electrode configuration on the thresh old stimulus for their excitation, were assessed. The threshold values were compared with those of dorsal column fibers. The results of this modeling study predict that, besides the well known influence of fibe r diameter, the curvature of the dorsal root fibers and the angle betw een these fibers and the spinal cord axis were of major influence on t heir threshold values. Because of these effects, threshold stimuli of dorsal root fibers were relatively low as compared to dorsal column fi bers. Excitation of the dorsal root fibers occurred near the entry poi nt of the fibers.