Restoration of fracture callus in osteopetrotic (op/op) mice by injection of macrophage colony-stimulating factor

Morphological studies on bone callus after fracture were carried out in nor mal and osteopetrotic mutant (op/op) mice, in which the tibiae diaphysis we re subjected to subperiosteal osteotomy. The fracture callus passed through apparently normal stages in normal mice. Normal osteogenesis with woven bo ne and occasional cartilage islands were observed in the absence of osteocl asts on the bone surface in op/op mice when macrophage colony-stimulating f actor (M-CSF) was not injected. When M-CSF was injected into the op/op mice , the bone fracture callus passed through the healing stages that resembled to the stages in the normal mice. These results indicate that the fracture callus in the op/op mice may be secondary to abnormalities in bone resorpt ion.