BACKGROUND: The changes in trabecular bone microarchitecture in osteoporosis have aroused much attention. The decrease in the number of trabecular nodes and increase in the number of free ends are found in osteoporosis, but the mechanism is still unclear.OBJECTIVE: To observe the trabecular remodeling process in ovariectomized rats as the osteoporosis models electron microscopically, and to explore the reasons for the decrease in the number of trabecular nodes and increase in the number of free ends.DESIGN: Randomized and controlled animal trial.SETTING: Department of Orthopedics, Third Hospital of Peking University.MATERIALS: The experiment was conducted in the Animal Laboratory, Third Hospital of Peking University from September 1999 to February 2000. Thirty-six female Wistar rats of 3 months old and 240-280 g were selected and randomly divided into ovariectomized group and control group with 18 rats in each group. The rats were observed at 4,8, and 12 weeks postoperatively with 6 rats at each time point.METHODS: The rats of ovariectomized group were subjected to ovariectomy 1 week after feeding, but the control group was not. The changes of proximal tibia trabecular microarchitecture was observed under scanning electron microscope at 4, 8 and 12 weeks, respectively, and the osteoclast, osteoblast, and structure of cell organs were observed under transmission electron microscope.MAIN OUTCOME MEASURES: [1]The re modeling process after ovariectomy by electron microscope; ②morphological changes of trabecular bone.RESULTS: [1]Scanning electron microscope observation showed that trabecular bone remodeling was distributed in every region of trabecular microarchitecture, especially St and Nd-St region. After ovariectomy, the transverse trabecular was easier to be perforated and broken; the trabecular network was almost intact at 4 weeks, but gradually damaged at weeks 8 and 12; moreover, the collagen fibers on the surface of trabecular bone were scrappy, disorder and thinner. ②By the transmission electron microscopic study, the tibial osteoclast were found active at 12 weeks. When absorbing cancellous bone, osteoclast closely adhered to its surface, and digitations stretched into the cancellous bone. The shape and size of digitations were significantly different, and around them, lucent area was observed. Osteoclast was polynucleation with abundant kytoplasm, and there were plenty of Golgi complex, smooth endoplasmic reticulum and mitochondrium. Lysosome inclusion compounds with different sizes and electron density were found in cells. Osteoblast was rarely found, and cell edge was rough, with bone lacuna.CONCLUSION: Bone remodeling is significantly active in St and Nd-St region of trabecular bone in ovariectomized rats.This may be the reason for the decrease in the number of trabecular nodes and increase in the number of free ends.