Reduced gap strains induce changes in bone regeneration during distraction

A bilateral New Zealand white rabbit model of distraction osteogenesis (DO) was used to investigate the relationship between strain environment and bo ne regeneration during limb lengthening. In seven (n = 7) rabbits, a stiffe ner was applied to the fixator on one side to reduce strains within the gap tissue after lengthening was completed. Animals were euthanized six days l ater and their distraction zones were harvested and analyzed for changes in new bone volume and architecture. Nonlinear finite element analyses (FEA) were performed to predict changes in the gap strain environment. FEA result s predicted a nearly uniform sevenfold decrease in average strain measures within the distraction zone. No change in total average new bone volume and significant decreases in both bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) were observed in tibiae in which gap strains were reduced experimentally, compared to contralateral controls. These results suggest that fixator stiffening influenced the architecture but not the amount of n ewly formed bone. This animal model of distraction might by used to study t he mechanisms by which strain fields affect events in bone repair and regen eration, such as cell proliferation, precursor tissue differentiation, and altered growth factor and nutrient delivery to tissues.