An ultrastructural observation of macrophages in rabbits' radius callus.

The ultrastructure of macrophages in rabbits' radius callus at the 14th and 31st day after fracture had been observed in the study. It was found that macrophages mostly appeared in the early stage callus where there were inflammation, clot, and bone chips. Commonly seen macrophages were active phagocytes with single nucleus, but they could evolve to form multinuclear macrophages or fuse into foreign body giant cells. We are therefore led to conclude that the functions performed by macrophages in healing callus are to phagocytize and digest damaged cellular fragments, small bone chips, clot and foreign body; to disrupt larger dead bone matrix extracellularly and to resorb them by microvilli-like processes on the surface of foreign body giant cells.