BONE REGENERATION AND FRACTURE-HEALING - EXPERIENCE WITH DISTRACTION OSTEOGENESIS MODEL

The relation between physical forces and the professes of bone regener ation and healing remains incompletely understood. Gaps in understandi ng of these processes stem in part from models that produce inadequate amounts of new bone for study. Bone created through the use of distra ction osteogenesis provides an attractive substrate for the study of m echanical forces and their effects on bone formation because this tech nique produces large volumes of new bone in a controlled fashion. The optimal mechanical environment in which bone formation occurs clinical ly has not been fully determined. In laboratory studies, however, the mechanical environment can be manipulated, and resultant changes in bo ne formation can be measured. To investigate how changes in strain env ironment influence patterns of bone formation, a bilateral New Zealand White rabbit model of bilateral distraction osteogenesis was implemen ted. When a stiffener was applied to the external distracter, computat ion analyses predicted a sevenfold to eightfold decrease in all strain measures. These reductions in gap strains appeared to induce signific ant decreases in bone volume fraction and mean trabecular thickness. W hen osteotomies were created at a 30 degrees angle to the bony axis to generate more shear within the gap tissue, changes in the distributio n of gap strains and resultant new bone architecture were observed. Sp ecific correlations between changes in tissue level strains and the pa ttern of bone regeneration were seen in both experiments. These result s provide direct in vivo evidence that pluripotential gap tissues are sensitive to their physical surroundings. Mechanisms responsible for t his sensitivity might include vascularity, stem cell supply, and scaff olding architecture. The process of bone formation in distraction oste ogenesis appears to be related to bone formation processes associated with more common conditions. The distraction osteogenesis model descri bed suggests a mechanism for bone formation that seems applicable to o ther more common processes associated with bone formation, including f racture hearing and impaired fracture healing.