Bone healing.

Secondary fracture healing with callus fomation involves the immediate reaction of this special kind of connective tissue (as well as others) with rapid increase in the reduplication of periosteal, paraosseal, and, to a lesser extent, endosteal cells. There is increased metabolism of glycosaminoglycan collagen synthesis, and transformation of fibrous and cartilaginous callus, combined with mineralization of the latter and intensified vascular invasion into bone. The glycosaminoglycan content decreases with progressing ossification, while the collagen content increases. In the beginning stages of whole bone fracture healing, vascularization is the first step responsible in part for the several maxima of synthesis and total contents of the specific cell products. Extension of ossification and remodeling in the final phases of bone fracture healing depend on other local and general factors, as well as biophysical and biological factors.