The healing of experimental fractures by compression osteosynthesis. II. Morphometric and chemical analysis.

The effects of rigid plate fixation on the structure and chemical composition of bones during healing of experimental fractures were studied by morphometric and chemical analysis at intervals of 3 to 24 weeks after attachment of six-hole AO plates to osteotomized rabbit tibiae. After fracture union gradual porotic transformation could be observed from 9 weeks onwards, with rapid excavation and breakdown of the cortical wall. During the study over 24 weeks the degree of porosity increased from 9.0 +/- 4.8 per cent to 37.5 +/- 10.2 per cent (P less than 0.001). This osteoporosis was accompanied by formation of new subperiosteal bone. The changes in the tubular bone led to a progressive increase in overall diameter and in the area occupied by the medullary cavity throughout the experiment. In the osteotomy area increased values were found for the content of hexosamines and the ratio of hexosamines to hydroxyproline at 3 weeks, indicating formation of connective tissue in the fracture area. Later on, no chemical signs of callus formation could be detected. In spite of the slight increase in the content by hydroxyproline, reflecting the formation of new bone subperiosteally, the chemical composition of the unresorbed cortical bone remained unchanged.