Non-invasive densitometric and histomorphometric study of the regenerated bone in the distraction gap in rabbits.

The long period of external fixation after the completion of distraction, which is necessary to obtain enough strength for resisting without fixation is a significant disadvantage of distraction osteogenesis. The purpose of this study is to understand the mechanical property of the regenerated bone and try to find an appropriate timing for safely removing the fixation device. An external fixation device was applied to the right tibia in rabbits and transverse osteotomy was performed just below the tibio-fibula junction. The tibiae were lengthened 7.2 mm at 0.72 mm a day for 10 days after surgery. A bone mineral density (BMD) and stress strain index (SSI) analyzed by peripheral quantitative computed tomography showed a significant increase on day 40, but returned to the control level at day 64 after the completion of distraction. Therefore, the newly formed bone between the host cortical bone seemed to be enough to resist the mechanical stress on day 40 during the consolidation period in this study. The present results suggested the possibility of removing the fixation device during the period when the BMD and SSI showed a significantly high level during the consolidation period.