MICROSTRUCTURAL INVESTIGATION OF THE EARLY EXTERNAL CALLUS AFTER DIAPHYSEAL FRACTURES OF HUMAN LONG-BONE

Microstructures of the early external callus after diaphyseal fracture s of human long bone were investigated by using scanning electron micr oscopy, X-ray diffraction, and transmission electron microscopy, It wa s found that the main structural framework of the human early callus c onsists of disordered, mineralized collagen fibrils with a small fract ion of regions of ordered collagen fibrils, X-ray diffraction analyses show that hydroxyapatite containing some carbonate impurity has been the dominant crystalline phase in the human early callus. In addition, a small amount of brushite phase was detected, Selected area diffract ion analyses indicated that hydroxyapatite microcrystals were embedded in microfibrils with a diameter of 4.5 nm and well-banded fibrils, wh ereas brushite particles of 15-20 nm in an irregular shape were locate d in the noncollagenous organic matter around the nonmineralized, orde red collagen fibrils, The spatial distribution of the brushite particl es in the human early callus was for the first time determined. The br ushite particles probably serve as the reservoir of calcium and phosph ate ions for subsequent mineralized periods rather than the precursor of hydroxyapatite. (C) 1995 Academic Press, Inc.