Flexure-Based Locking Plates Can Modulate Interfragmentary Motion in Distal Femur and Diaphyseal Fractures: A Parametric Finite Element Analysis

Axial interfragmentary motion is known to stimulate fracture healing. A mechanically compliant fracture fixation plate incorporating flexures is proposed to provide controlled axial micromotion to long bone fractures. To explore the concept's feasibility, computational modeling of general diaphyseal and distal femur fractures treated with both rigid and compliant plates is conducted. In Part I of this study, a diaphyseal fracture finite element model for novel compliant plates is validated against experimental data with good agreement. In Part II, a parametric analysis is conducted using the validated model to characterize the performance of many compliant plate designs with varying geometry and materials. Under axial loading, all compliant plate configurations provided greater magnitude (1.03mm vs. 0.22mm) and symmetry (270-390%) of axial interfragmentary motion than rigid plates. Steel compliant plates with thicker flexures (0.3-0.6mm) may provide the best performance given their enhanced motion and comparable bending/torsional rigidity. In Part III, compliant plates are adapted for use in treating distal femur fractures. Results demonstrate that compared to a rigid plate, a compliant distal femur plate with increased thickness can effectively modulate interfragmentary motion - that is, increase the insufficient near cortex motion under low loads (from 0.14mm to 0.23mm) and reduce the excessive far cortex motion under large loads (from 7.96mm to 2.54mm). Flexure-based locking plates represent a promising new approach to treating diaphyseal and/or distal femur fractures. Additional research is needed to investigate vivo performance.