In an effort to define and characterize the initial mineralization
product of fracture-healing, we studied the mineral components within a
model of endochondral osseous repair. Fracture calluses from the tibiae of
rats and rabbits undergoing endochondral fracture-healing were analyzed, in
toto and following density fractionation, by physicochemical and
crystallographic techniques. Significant changes in mineral composition,
crystal size, and density occurred in the early phases of fracture repair.
In the rat, two weeks after fracture, the calcium-to-phosphorus ratio was
higher than that of the mineral component, possibly due to calcium-binding
to some of the macromolecules known to be present. The earliest mineral was
poorly crystallized hydroxyapatite with a high carbonate content. Crystal
perfection improved rapidly and approached that of normal diaphyseal bone
within eight weeks after endochondral fracture in both the rabbit and the
rat.