Reverse Dynamization Accelerates Regenerate Bone Formation and Remodeling in a Goat Distraction Osteogenesis Model

Background: The concept of reverse dynamization involves modifying the mechanical environment surrounding a fracture to influence the healing response. Initially, less rigid stabilization is performed to allow micromotion, encouraging cartilaginous callus formation. This is followed by a conversion to more rigid fixation to prevent the disruption of neovascularization, thereby accelerating bone healing and remodeling. The effect of reverse dynamization in distraction osteogenesis has not been studied, to our knowledge. The aim of this study was to determine whether reverse dynamization can accelerate the formation and maturation of regenerate bone in a goat distraction osteogenesis model. Methods: Midshaft tibial osteotomies were created in 18 goats and stabilized using circular external fixation. After a 5-day latency period, 4 weeks of limb distraction began to obtain a 2-cm gap; this was followed by 8 weeks of regenerate consolidation. The goats were divided into 3 groups: static (rigid) fixation (SF, n = 6); dynamic fixation (DF, n = 6), consisting of continuous micromotion using dynamizers; and reverse dynamization (RD, n = 6), consisting of initial micromotion during the distraction period using dynamizers followed by rigid fixation during the consolidation period. Healing was assessed using radiographs, micro-computed tomography, histological analysis, and mechanical testing. Results: Radiographic evaluation showed earlier regenerate formation in the DF and RD groups compared with the SF group. After the distraction and consolidation periods were completed, the regenerate formed under the conditions of RD had less trabeculation, higher bone mineral density, and smaller total and bone volumes, and were stronger in torsion compared with the SF and DF groups. This appearance is characteristic of advanced remodeling, returning closest to the values of intact bone. The DF group also had evidence of an interzone (radiolucent fibrous zone) at the end of the consolidation period. Conclusions: Application of the reverse dynamization regimen during distraction osteogenesis accelerated formation, maturation, and remodeling of regenerate bone. Clinical Relevance: The findings of this study have important implications in the clinical setting, as reverse dynamization may lead to shorter treatment times and potentially lower prevalence of complications for patients needing distraction osteogenesis.