Role of fracture hematoma and periosteum during fracture healing in rats: interaction of fracture hematoma and the periosteum in the initial step of the healing process.

To study the mechanisms of fracture healing, we investigated the interaction between fracture hematoma and periosteum during the early phase of fracture healing in rats. Experimentally induced fractures of the tibia in untreated rats were compared histologically with such fractures in rats in which either the bone marrow or the periosteum had been removed. The extent of periosteal cell proliferation and chondrogenesis in the fracture hematoma was evaluated on experimental days 3, 6, 10, and 14. On day 3, periosteal cell proliferation at the tibial fracture site was decreased in the bone marrow-removed rats compared with the proliferation in untreated rats. Little chondrogenesis in the fracture hematoma was seen through day 6 in the periosteum-removed rats. These results suggest that the periosteum is important for mediating the primary steps of chondrogenesis and enchondral ossification in the fracture hematoma and that the fracture hematoma may be essential for periosteal cell proliferation during fracture healing.