Mast cells in fracture healing: an experimental study using rat model.

To investigate the role of mast cells in wound healing process, the time course of appearance and distribution of mast cells were examined during fracture healing in rats. In the early phase of fracture healing, mast cells appeared in the original marrow adjacent to the internal callus. In later phases, mast cells appeared in the newly formed marrow in the external callus. In the external callus the number of mast cells reached a peak at around 5 weeks after fracture when remodeling was progressing. At this phase, the number of mast cells in the convex side of the fracture was significantly greater than that in the concave side. These results suggest that mast cells promote bone resorption, especially during remodeling of callus formed at the fractured site.