The contribution of the dorsal and ventral roots of the tibial nerve in the propagation of the spinal somatosensory evoked potential in cats.

This study employed selective unilateral dorsal and ventral rhizotomy to examine the contribution of both the dorsal and ventral roots of the tibial nerve in the induction of the spinal somatosensory evoked potential (SSEP) in the cat. The spinal roots of origin of the tibial nerve in the cat were determined by retrograde transport of horseradish peroxidase (HRP). Spinal roots L6, L7, and S1 were found to give rise to the cat tibial nerve. Physiologic monitoring showed that the dorsal roots at these levels primarily contribute to the induction of the SSEP, but the ventral roots also make a small contribution. Because bilateral tibial nerve stimulation was found to mask a root injury on one side, we recommend sequential unilateral peripheral nerve stimulation when using SSEP during operations on the spine.