[Effects of 1.8 mT sinusoidal alternating electromagnetic fields of different frequencies on bone biomechanics of young rats].

To study the effects of 1.8 mT sinusoidal electromagnetic fields of different frequencies on bone mineral density (BMD) and biomechanical properties in young rats. A total of 32 female SD rats (6-week-old) were randomly divided into 4 groups (8 in each):control group, 10 Hz group, 25 Hz group and 40 Hz group. The experimental groups were given 1.8 mT sinusoidal electromagnetic field intervention 90 min per day. The whole body BMD of rats was detected with dual-energy X-ray absorptiometry after 4 and 8 weeks of intervention. After 8 weeks of intervention, all rats were sacrificed, and the BMD of femur and lumbar vertebra, the length and diameter of femur, the width between medial and lateral malleolus were measured. Electronic universal material testing machine was used to obtain biomechanical properties of femur and lumbar vertebra, and micro CT scan was performed to observe micro structures of tibial cancellous bone. Compared with the control group, rats in 10 Hz and 40 Hz groups had higher whole body BMD, BMD of femur, maximum load and yield strength of femur, as well as maximum load and elastic modulus of lumbar vertebra (all <0.05). But no significant differences in the length and diameter of femur, and the width between medial and lateral malleolus were observed between control group and experimental groups (all >0.05). Micro CT scan showed that the trabecular number and separation degree, bone volume percentage were significantly increased in 10 Hz and 40 Hz groups (all <0.01). Rats in 25 Hz group also had higher BMD and better in biomechanical properties than control group, but the differences were not statistically significant (all >0.05). 10 and 40 Hz of 1.8 mT sinusoidal electromagnetic field can significantly improve the bone density, microstructure and biomechanical properties in young rats.