| Objective: Bone quality and bone morphogenesia are determined by its genetic background, but the structure and function of bone depend much on its stress environment, which has been widely accepted. In Wolff's Law of Bone Turnover, it is thought that there is an exactly correspondent relationship between bone structure and its stress environment, and bone has an adaptation to its external stress condition. A number of experimental studies have revealed that mechanical stress can result in the correspondent changes of bone structure through inducing bone remodeling (a dynamic equilibrium between bone resorption and bone formation).In this study, we investigated the effects of different stress environments on bone growth, bone remodeling and biomechanical properties in growing female rats by creating a new animal experimental model.Materials and methods: Sixty 5-week-old female Sprague-Dawley rats, 150-170g body weight, were used in this study. Right hindlimbs of 40 rats were performed sciatic neurectomy to become cripple and served as unloading group; left hind limbs thus bore excess load and were served as overloading group. The left 20 rats were served as control group after their right sciatic nerves were exposed without resection. After operation, all rats were housed individually and provided standard rat chow. Every day the animals were encouraged to exercise for half an hour in the morning, at noon and in the evening. The bone mineral density (BMD) of femur and body mass were measured once a week. The study period was 7 weeks. On the last day of the 7th week, the femurs and tibias were removed from each rat .The tibial samples were used for histological analyses after HE staining and Masson staining. The femoral samples were performed computed tomography measurement, morphometric measurement and biomechanical testing. Data were presented as means±SD. Dunnet-t test was used in the statistical analysis. Result: The body weight of rats increased gradually every week, the increasement of the first week was lower than other time and the difference had no statistical significance (p>0.05). Femoral BMD of the three groups all decreased at the first week and then gradually increased until the 6th week when the femoral BMD became stable. The overloading group had a higher femoral BMD meanwhile the unloading group had a lower femoral BMD as compared with the control group. The differences between groups both had statistical significance (p<0.05).There was no difference between the femoral length of the three groups. The femoral wet mass, dry mass, ashed mass and ash density were lower in the unloading group and higher in the overloading group as compared with the control group (p<0.05). Significant differences were observed in the biomechanical properties: The femurs of the unloading group had a lower maximum load, maximum stress, maximum strain, Young's modulus and maximum deformation, but a higher stiffness than the control group; however the femurs of the overloading group had a higher maximum load , maximum stress, maximum strain and Young's modulus than the control group. HE staining showed that the tibial trabecula of the unloading group became less and thinner which was more and thicker in the overloading group in comparison with the control group. Masson staining indicated that the unloading group had less bone mineral components than the control group and its bone matrix had been malmineralized, in contrast, the overloading group had much more bone mineral content than the control group and its bone matrix had been well mineralized.Conclusion: Different stress environments can result in the changes of bone mineral density, bone mophometric and biomechanical properties of rapidly growing female rats. High stress induces bone remodeling and mainly through bone formation, as a result, the BMD, the morphometric properties and biomechanical parameters are higher than that of the normal rats; low stress produces bone remodeling mainly through bone resorption thus result in a lower BMD, morphometric a...
|
PDF Full Text Request