EXPRESSION OF 4 GROWTH-FACTORS DURING FRACTURE REPAIR

Fracture repair offers an opportunity to study the physiology of bone formation at the fracture site. Isolation of growth factors from bone matrix has implicated growth factors as participants in bone physiolog y. We therefore examined the expression patterns of aFGF, IGF-I, PDGF, and TGF-beta during fracture repair. An animal model has been develop ed to study repair of tibial fractures. The model provides both reprod ucible and quantifiable results, allowing the fracture repair process to be divided into four stages (Bourque ef al., Lab. Anim. Sci 42: 369 -374, 1992). Fractured tibiae were examined immunohistochemically with polyclonal antibodies to four growth factors. PDGF was visualized in macrophages in close proximity to the periosteum during stage 1. aFGF was visualized in cells of the expanded cambial layer and was associat ed with a rapid increase in the population of fibroblast-like mesenchy mal cells during stage 2. IGF-I was visualized in young chondroblasts at the edge of the cartilage mass replacing the fibrous callus during stage 3. TGF-beta was visualized in calcified matrix producing chondro cytes at the edge of ossification fronts penetrating the cartilage cal lus during stage 4. The immunohistochemical results suggest that these growth factors act as local simulators of the repair process.