A distraction osteogenesis model to investigate the influence of the mechanical environment on bone formation.

Abstract

Bone formation is an important physiologic process for skeletal growth, maintenance, and repair. The purpose of this work was to investigate the influence of the mechanical environment on bone formation using a distraction osteogenesis model. The first study investigated the morphology and timing of bone formation in a canine tibial lengthening model of distraction osteogenesis. The results of this study indicated the immediate post-distraction period as a time of active bone formation. After the development of a New Zealand white rabbit model of bilateral tibial lengthening, subsequent studies investigated the histology of the bone formation process and the mechanical environment acting during this period. The bone formation of distraction osteogenesis is focused at the interface between existing proximal and distal masses of longitudinally oriented trabeculated new bone and the central unmineralized fibrous and canilaginous tissues. The mechanical environment in the post-distraction period is dominated by the relatively stiff external fixator and the loads applied during functional activity. The low stiffness gap tissues experience relatively constant tension and cyclic strains on the order of 15%. The final study investigated the effect of stiffening the external fixator to reduce the cyclic strains and found a significant change in the bone formation process in terms of new bone architecture and cellular activity. The results of these studies have important implications for our understanding of bone formation in distraction osteogenesis, for the clinical use of distraction osteogenesis, and for future research investigating bone formation.