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Abstract
Electrical stimulation with a 60 kHz sinewave input signal, supplied via electrodes on the skin surface, is presently being studied as a treatment for human systemic osteoporosis. The purpose of this thesis is to determine the ideal electrical stimulation device design in terms of the type and placement of the electrodes and magnitude of the input current necessary to produce reversal of the osteoporotic process. Initially, the electric field and current density distributions were found in the various tissues of a mathematical model of the experimental Sprague Dawley breeder 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 input signal applied via skin electrodes. A parametric study was done to determine the principle factors which effect the field in the vertebral bodies. Two pair of transversely placed stainless steel electrodes spaced by at least three vertebral bodies, produced the most uniform field distributions. This was the electrode system used by Luessenhop to show significant reversal of osteoporosis in the experimental Sprague Dawley breeder rat with a 100 microamps, 60 kHz sinewave signal applied to each pair of electrodes. This thesis then determined the range of current density values in the trabecular bone of the rats in that experiment to be 3.0 $\times$ 10$\sp{-6}$ to 5 $\times$ 10$\sp{-6}$ amps/cm$\sp2$.
Based on these experimental and theoretical determinations, the magnitude of the input current to the electrodes necessary to induce a response in the human vertebral body was determined. Using the same finite element methods as in the rat study, the potential and current density values at nodal points were found in a three-dimensional, anatomically-based, finite element grid model of the human, constructed from T$\sb5$ to L$\sb5$. Four different electrode systems in current clinical use were evaluated, and the optimal input current (that which produced the current density found in the experimental rat to reverse osteoporosis) was determined. A single pair of transversely placed strip electrodes with high electrical conductivity was determined to be optimal.
