Histomorphometry Of Distraction Osteognesis By Modificated Hoffman External Fixators In Rabbit: Model And Effect Of The Active Weight-bearing

[Abstract] Purpose : Made the animal model of Distraction Osteognesis by modificated Hoffman external fixators in rabbit tibia. To investigate the mode and influential factor of new bone formation following Distraction Osteognesis in tibial distraction.Materials and methods : Forty-five rabbit were osteotomied on right tibia shaft,were fixed with custom-made Hoffman fixators. Distraction was started 7 days after operation, at rate of 0.5mm/12h for 10 days (total 10mm elongation). The rabbits were evaluated with radiographs every week until the eighth week after distraction. Five of them were killed just after the distraction,and every week of consolidation until the eighth week. The specimens performed histomorphometric analysis,radiographs analysis and mechanical test. All specimens were stained with hematoxlin-eosin and masson. Another 10 rabbits were distraction on right tibia as the same methods,were allocted to two group. One group were fixed with telescoping fixators just after distraction, for two weeks consolidation, allow them active weight-bearing. Two group were killed after two weeks consolidation. Contrast the two group with histomorphometry, radiographs and torsional stiffness.Results :The model of Distraction Osteognesis in rabbit tibia by Hoffman fixator is successful. The findings of histomorphometryshow that the Distraction Osteognesis includes intrameubranous ossification, enchondral ossification, bone regeneration,and bone remodeling. The intrameubranous is the predominant mechanism of ossification. At the location of the distraction formed a new bone growing center. The local stress focus bring about the enchondral ossification taking place. The new bone tissue derived from the periosteum, so protecting the periosteum whole is most important. The ossification and remodeling spend at22004least 6 weeks. We found a significant increase of ossification take place in the group with active weight-bearing. And the stiffness of the callus is higher than the contrast(p<0.05). Active weight-bearing accelerate regenerate bone healing and remodeling.Conclusions : In Distraction Osteognesis, avoiding the stress focus and protecting the periosteum whole are most important. These findings suggest the active weight-bearing to be quite effective in early bony consolidation in Distraction Osteognesis. Additional studies will be required to determine the optimal loading for new bone formation.