Comparative biochemical studies of the callus matrix in immobilized and non-immobilized fractures

Fracture healing in both non-immobilized and immobilized rat fracture callus, though different radiographically and histologically; is characterized by similar biochemical changes in the ground substance. Although the callus formed in the immobilized model is appreciably smaller than that formed when the fracture is not immobilized, the chemical composition of the organic matrix of the existing callus undergoes similar modifications regardless of fixation and histological response. Previous studies of endochondral fracture repair have demonstrated an elevation in fracture callus hexosamine content during the early stages of healing of the non-immobilized fracture. This corresponded histologically to a predominance of cartilaginous tissue in the callus matrix. In the present study, the biochemistry, histology, and roentgenographic features of stabilized and non-stabilized rat fractures are compared. Similar elevations in hexosamine are noted at two weeks in both models. These elevations are attributed to changes in proteoglycan rather than glycoprotein concentration of the tissue.