Comparison of bone regeneration rate in flat and long bone defects: Calvarial and tibial bone

An ideal scaffold for bone tissue regeneration should be dissolved at the same rate of host bone growth into the defect. Therefore, to produce such a scaffold, it is necessary to obtain a standard healing rate of bone defects. In this study, we compared healing rate of bone defects in calvarial and long bones, which have differential developmental and regenerative mechanisms. In the calvaria and tibia, 3 mm defects were made, and healing was analyzed using microcomputed tomography (microCT) and histology up to six weeks. MicroCT analysis showed that in calvarial defects, an unhealed gap remained until six weeks, whereas tibial defects had healed after three weeks. H&E and Trichrome staining consistently showed that calvarial defects were not completely healed by six weeks, however, a tibial defect started to heal from three weeks. Results of histomorphometric analysis showed that 60% of calvarial defects had healed at six weeks after surgery, whereas 80% of tibial defects showed regeneration at three weeks. Cartilage formation was detected only in tibial defects, suggesting endochondral regeneration in long bone, but not in flat bone. Collectively, these results demonstrate that healing of a long bone defect is faster than that of flat bone by approximately two folds. Therefore, our data suggest that dissolution of scaffold should be optimized based on the type of bone defect.