Strain-related bone remodeling in distraction osteogenesis of the mandible.

Distraction osteogenesis has become a mainstay in craniofacial surgery. However, there are several unresolved problems concerning the biology of bone regeneration. We investigated the biomechanical effects of mandibular lengthening in 32 rabbits on a cellular and histologic level. The mandible was subjected to a corticotomy, held in a neutral position for 4 days, and then lengthened at various strain rates and frequencies for 10 days. Radiographic, histologic, and electron microscopic examinations showed a strain-related bone regeneration. Application of physiologic strain rates (2000 microstrains or 0.2 percent) led to a bridging of the artificial fracture exhibiting woven ossification, whereas at 20,000 microstrains trabecular bone formation was demonstrated. In contrast, hyperphysiologic strain magnitudes (200,000 microstrains and 300,000 microstrains) showed a fibrous tissue formation. Multiple strain applications (10 cycles/day versus 1 cycle/day) increased the width of the distraction gap without changing the stage of bone regeneration. The gradual distraction of bone in physiologic magnitudes at higher frequencies seems to be desirable for a bony differentiation and may help to improve clinical applications.