AN ANIMAL MODEL TO EVALUATE THE EFFECT OF ECCENTRIC CORTEX OVERDRILLING IN THE DYNAMIZATION OF LOCKING PLATE SYSTEM

This research focuses on application of the over-drilling technique in an animal model to evaluate its biological impact on fracture healing. While synthetic bone models provide a reliable platform for assessing biomechanical effects, they lack the ability to replicate the biological processes critical for bone repair, such as cellular activity, vascularization, and remodeling. In this study, a rabbit tibial osteotomy model was utilized to investigate the mechanical and biological outcomes of fixation with and without near cortex over-drilling of varying diameters. Following sacrifice, radiological analysis via quantitative computed tomography, histological evaluation, and mechanical testing upon torsional loading were performed. The findings revealed no significant differences in BV/TV, Tb.Th, Tb.Sp, or bone stiffness between the control and over-drilled groups. However, the over-drilled constructs demonstrated statistically significant improvements in mechanical properties, with failure occurring at twice the torque and four times the peak rotational energy compared to controls. The control group exhibited greater resistance to deformation under torsional loading, likely due to the denser, immature woven bone present during earlier phases of healing. Conversely, the brittle nature of this bone possibly resulted in lower peak torque to failure under torsion. Superior peak torque and rotational energy observed in the over-drilled group suggest increased toughness and enhanced ability to absorb energy before fracture. Histological analysis further indicated that the over-drilled group had progressed to the remodeling phase, characterized by trabecular formation and a supportive granulation tissue environment. In contrast, the control group remained in earlier stages of repair, with signs of necrosis. These results suggest that over-drilling the near cortex promotes advanced fracture healing by reducing construct stiffness and enhancing bone remodeling. This technique offers a simple, cost-effective approach to dynamize the locking plate system and optimize the mechanical environment for fracture repair, alternative to dynamic locking screws as demonstrated in this animal model.