Effects of internal fixation with simvastatin coating on healing of rat osteoporotic fractures at late period / 中国组织工程研究

ABSTRACT

BACKGROUND:As a lipid-lowering drug, simvastatin has been proved to be effective in promoting bone formation. Previous studies have demonstrated that local y applied simvastation accelerated fracture healing at middle phase in osteoporotic rats, while no study focuses on the influence of local y applied simvastatin on fracture healing at late period in an osteoporotic rat. OBJECTIVE:To investigate the effect of simvastatin local y applied from a bioactive polymer coating of implants on osteoporotic fracture healing at late period. METHODS:Female Sprague-Dawley rats were divided into sham group, osteoporotic fracture group and simvastatin group. In the sham group, the abdominal cavity was exposed without ovariectomy. Six weeks later, femur fracture models were established in normal or osteotoporotic Sprague-Dawley rats, and intramedul ary stabilization was achieved with uncoated titanium Kirschner wires in normal rats (sham group),with polylactic acid coated titanium Kirschner wires (osteoporotic fracture group) and with simvastatin/polylactic acid coated titanium Kirschner wires (simvastatin group). Femurs were harvested after 12 weeks, bone mineral density was determined with dual X-ray absorptiometry, and then radiographic and histological analysis was performed for analysis of fracture healing. Immunohistochemical evaluation was employed for bone morphogenetic protein 2 expression. RESULTS AND CONCLUSION:The bone mineral densities of both the total fractured femur and fractured site 12 weeks after fracture in the osteoporotic fracture group and simvastatin group were markedly decreased compared to normal fractured rats. The bone mineral density of the fractured site was significantly higher in the simvastatin group than the osteoporotic fracture group. Radiographic results demonstrated completely finished cal us remodeling in the sham group;poor healing, pale cal us density and blurred fracture line were seen in the osteoporotic fracture group;disappearance of fracture line, bone defects fil ed with cal us, and deep periosteal reaction were found in the simvastatin group. X-ray scores in the sham and simvastatin groups were significantly higher than that in the osteoporotic group (P<0.05). Hematoxylin-eosin staining showed a delayed healing process in the osteoporotic group, and revealed a significantly processed cal us with regular-shaped newly formed bone trabeculae in the simvastatin group. Immunohistochemical evaluation showed no significant difference in the bone morphogenetic protein 2 expression between any two groups. These findings suggest an improved fracture healing under local application of simvastatin in osteoporotic rats.