engleski

Improved Healing of Large Segmental Defects in the Rat Femur by Reverse Dynamization in the Presence of Bone Morphogenetic Protein-2

Large segmental defects in bone do not heal well and continue to present clinical challenges. This study investigated the effects of modulating the mechanical environment as a means of improving healing. Although the influence of mechanical forces on the healing of fractures is well established, there are no previous papers describing their influence on the healing of large segmental defects. Based upon theoretical considerations, we hypothesized that healing would be improved by initial, low stiffness fixation of the defect, followed by high stiffness fixation during the healing process. We call this “reverse dynamization”. A rat, femoral, critical size defect model was used. External fixators were constructed to provide different degrees of stiffness and, importantly, the ability to change stiffness during the healing process in vivo. Healing of the critical size defects was initiated by the implantation of 11 g recombinant, human BMP-2 on a collagen sponge. Groups of rats were allowed to heal under conditions of low, medium and high stiffness, as well as under conditions of reverse dynamization where the stiffness was changed from low to high at 2 weeks. Healing was assessed at 8 weeks by X-ray, histology, micro-computed tomography, dual energy X-ray absorptiometry, and mechanical testing. Under conditions of constant stiffness, the low stiffness fixator produced the best healing after 8 weeks. However, reverse dynamization considerably improved upon this, and resulted in a dramatic acceleration of the healing process by all the criteria of this study. The histological data suggest that this was the result of intramembranous, rather than endochondral, ossification. Reverse dynamization accelerated healing in this rat femoral model and is worthy of further investigation as a means of improving the healing of large segmental defects. Clinical Relevance These data provide the basis of a novel, simple and inexpensive way to improve the healing of critical size defects in long bones. The data may also be applicable to other circumstances where bone healing is problematic

bone healing; BMP-2; bone defects

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