EVALUATION OF THE MECHANICAL ENVIRONMENT DURING DISTRACTION OSTEOGENESIS

Physical forces have been hypothesized to direct the process of bone r egeneration during distraction osteogenesis. However, despite signific ant clinical experience, relatively little is known about how the mech anics of distraction influence bone formation. This study investigated net fixator forces and strains in the distraction callus during bilat eral lengthening of tibiae in New Zealand White rabbits, Distractions yielded a classic viscoelastic response with a sharp increase in fixat or force, followed immediately by significant relaxation. Tension acti ng on mesenchymal gap tissue caused by distraction was estimated to re ach more than 30 N by the time full lengthening was achieved, Average maximum cyclic strains within the distraction zone during ambulation w ere estimated to be 14% to 15% and supported by the results of fluoros copic imaging, Paradigms for fracture healing have hypothesized that s uch strains are incompatible with new bone formation. The documented c linical success of distraction osteogenesis at stimulating large volum es of new bone suggests that other mechanisms that warrant additional investigation may be at work during distraction.