The cellular events of intramembranous and endochondral ossification in rat fracture healing

Objective: To observe the changes of cellular events in intramembranous and endochondral ossification during fracture repair in rats. Methods:Closed rat femoral fractures were produced. The callus specimens were excised from the 3rd to the 17th day after fracture, and were stained to observe the histological changes of cells in newly formed trabecular bone, cartilage, endochondral ossifications, and bone remodeling. Results:Intramembranous ossification started from the 3rd day,and mature trabecular bone was observed on the 7th day. Cartilage tissue appeared 3 to 5 days after fracture. Endochondral ossification was observed 7 to 9 days after fracture. Remodeling in newly formed trabecular bone and underling cortical bone started on the 7th and the 9th day, respectively. Conclusion:The histological changes of cells during the process of fracture healing are highly ordered. The cellular events of intramembranous ossification, cartilage formation, endochondral ossifications,and bone remodeling appear in the callus simultaneously or sequentially.