Calculated spinal cord electric fields and current densities for possible neurite regrowth from quasi-DC electrical stimulation.

The prime goal of this work was to model essentially steady (DC) fields from electrodes, implanted in several ways, which have been suggested as possible means to encourage nerve fiber regrowth in spinal cord injuries. A simplified model of the human spinal cord in the lumbar region and the SEMCAD-X computer program were used to calculate electric field and current density patterns from electrodes outside vertebrae and those inserted extradurally within the spinal canal. DC electric fields guide nerve growth in developing organisms and in vitro. They also have been shown to encourage healing of injured peripheral nerves, and application of a longitudinal field has been used in attempts to bridge spinal cord injuries. When calculated results are scaled to the experimental level used in the literature, all modeled electrodes produced fields in the spinal cord below fields needed in the literature for stimulation of spinal as well as peripheral nerve growth in vitro, in dogs, and in a published clinical human trial. The highly-conducting cerebrospinal fluid appeared to provide effective shielding; there was also a very high degree of polarization at electrodes.