Background: Decreasing the stiffness of locked plating constructs can promote natural fracture healing by controlled dynamization of the fracture. This biomechanical study compared the effect of four different stiffness reduction methods on interfragmentary motion by measuring axial motion and shear motion at the fracture site.
Methods: Distal femur locking plates were applied to bridge a metadiaphyseal fracture in femur surrogates. A locked construct with a short bridge span served as the non-dynamized control group (LOCKED). Four different methods for stiffness reduction were evaluated: replacing diaphyseal locking screws with non-locked screws (NON-LOCKED); bridge dynamization (BRIDGE) with two empty screw holes proximal to the fracture; screw dynamization with Far Cortical Locking screws (FCL); and plate dynamization with active locking plates (ACTIVE). Construct stiffness, axial motion and shear motion at the fracture site were measured to characterize each dynamization methods.
Results: Compared to LOCKED control constructs, NON-LOCKED constructs had a similar stiffness (p=0.08), axial motion (p=0.07), and shear motion (p=0.97). BRIDGE constructs reduced stiffness by 45% compared to LOCKED constructs (p<0.001), but interfragmentary motion was dominated by shear. Compared to LOCKED constructs, FCL and ACTIVE constructs reduced stiffness by 62% (p<0.001) and 75% (p<0.001), respectively, and significantly increased axial motion, but not shear motion.
Conclusions: In a surrogate model of a distal femur fracture, replacing locked with non-locked diaphyseal screws does not significantly decrease construct stiffness and does not enhance interfragmentary motion. A longer bridge span primarily increases shear motion, not axial motion. The use of FCL screws or active plating delivers axial dynamization without introducing shear motion.
This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.
Copyright (C) 2017 Wolters Kluwer Health, Inc. All rights reserved.
