Background: This study was designed to investigate the process of bone formation caused by implantation of octa calcium phosphate (OCP) in rat tibiae.

Methods: We used 25 young male Sprague-Dawley rats. A full thickness standardized trephine defect, 3-mm in diameter, was surgically created on the superior end of right and left tibia. Amount of 6-mg synthetic Octa calcium Phosphate was implanted into a bony defect on the right tibia as a experimental group. No OCP particles were implanted in the left tibia as a control group that was otherwise treated identically. Bone formation was examined histologically on 7th, 10th, 14th, 21st, 28th days after implantation.

Results: In the experimental group, on the 7th day after implantation, a few clusters of cartilage cells were observed between the OCP particles near the defects margin. Osteogenesis was initiated locally between the OCP particles in central position of the defects on 10th day after implantation. By 14th day after implantation, Alcian blue staining showed hypertrophic chondrocytes that replaced by new bone. In addition to bone formation locally around the OCP particles, more apposition of new bone was observed near the defects margin on 14th and 21st days after implantation. At the end of study implanted OCP was surrounded by newly formed bone. In the control group, at the end of study, bone formation was observed only along and near the defects margin.

Conclusion: These results demonstrate that octa calcium phosphate could be used in the repair of the long bone defects.