Field distribution in vertebral bodies of the rat during electrical stimulation: a parameter study

Electrical-field and current-density distributions were found in various tissues of a mathematical model of an experimental rat used to study systemic osteoporosis. The finite-element method was used to solve the boundary value problem derived from Maxwell´s equations using a quasistatic approximation for a 60-kHz external output signal applied by means of skin electrodes. A parametric study was done initially to determine the principle factors which effect the solution of the field in the vertebral bodies. Grid coarseness, model length, intervertebral space width had little effect on the solution while trabecular bone and abdominal cavity conductivity values had strong effects. The two pairs of transversely placed electrodes spaced by at least three vertebral bodies produced the most uniform field distributions and were used in the experimental rat model. The range of current density values in the trabecular bone was determined to be 3.0-5.0 mu A/cm ² at the external output signal where evidence of a reversal of bone loss due to castration osteoporosis had been found in the experimental rat.