Electrical properties of bone as a function of age, immobilization and vibration

Changes in electrical characteristics of rat tibiae were investigated as a function of age, immobilization, and vibration and were related to compositional and structural changes in the femurs of these animals. The increase in cortical bone conductivity corresponds to the age-dependent increase in the inorganic portion of bone and bone density. This suggests that since physiological electric fields would be dissipated more quickly in older bone, bone growth responds to the electric fields rather than current. Conductivity is decreased following bone demineralization by immobilization. Since the bone is being adapted to the immobilization by decreasing growth in terms of bone weight, volume, and cortical area, the results indicate, as in bone growth with age, that the physiological electric fields are the important parameter in directing bone growth. Conductivity, as well as bone growth, is unaffected in rat limbs following prolonged exposure to vibration.