Beschreibung:
<jats:sec><jats:title>Purpose</jats:title><jats:p>In humans, fractures of the long bones mainly occur in the metaphysis such as distal radius. However, most studies of the bone repair process have focused on the diaphysis region, thus little has been reported on the metaphysis repair process. In this study, we compared the bone repair process between the metaphysis and the diaphysis of the mouse tibia.</jats:p></jats:sec><jats:sec><jats:title>Materials and Methods</jats:title><jats:p>Bone apertures were formed in the tibial metaphysis and diaphysis of mice by 0.8mm drill hole. At indicated times after the surgery, samples were collected, and examined by histomorphometrical (micro‐computed tomography), histological (toluidine blue), histochemical (alkaline phosphatase (ALP)), and immunohistochemical (osteocalcin and type I collagen) analyses. Quantitative real‐time PCR was used to analyze the expression of mRNAs in the periosteum (<jats:italic>sox9</jats:italic>, <jats:italic>type 2 collagen</jats:italic>) and bone marrow (<jats:italic>osterix</jats:italic>, <jats:italic>runx2</jats:italic>, <jats:italic>type 1 collagen</jats:italic>).</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>In the metaphysis, cartilage formation was not detected during the repair period on the periosteum side. The bone aperture was filled with newly formed bone developed from bone marrow at 7 days, and then gradually decreased. In the diaphysis, cartilage was formed around the bone aperture at day 4 and sequentially replaced by bone on the periosteal side. Periosteal callus peaked at day 14, and then remodeled to original architecture. Medullary callus gradually increased to day 14, and the aperture filled with medullary callus transiently at day 14, then medullary callus rapidly resorbed at day 21. In both sites, bone mineral density (BMD) was gradually restored at the bone aperture. At day 14, BMD was higher in the metaphysis than in the diaphysis, but the diaphysis showed significantly high BMD at day 42. In diaphysis, the expression of <jats:italic>type 2 collagen</jats:italic> mRNA reached to the peak at day 5 following the peak expression of <jats:italic>sox9</jats:italic> mRNA reached to the peak at day 4 on the periosteum. However, in the metaphysis, expression of those mRNAs was lower than the diaphysis. Expression of the osteogenic markers in bone marrow, alkaline phosphatase, osteocalcin and type I collagen, appeared earlier in the metaphysis than the diaphysis. In the metaphysis, <jats:italic>osterix</jats:italic>, <jats:italic>runx2</jats:italic> and <jats:italic>type 1 collagen</jats:italic> mRNAs were markedly upregulated compared with the diaphysis.</jats:p></jats:sec><jats:sec><jats:title>Discussion</jats:title><jats:p>These results indicate a difference in the bone repair process between the metaphysis and the diaphysis, suggesting a functional heterogeneity of the periosteum and bone marrow mesenchymal cells in response to bone fracture.</jats:p></jats:sec>