Preventing Iatrogenic Fibula Fractures Using the Push-Pull Technique: A Biomechanical Comparison of Unicortical Versus Bicortical Post Screws.

Abstract

Displaced diaphyseal fractures can be reduced using the push-pull technique, wherein a plate is affixed to the distal fragment of the fracture, a post screw is placed proximal to the plate, and a lamina spreader creates distraction. This study evaluated the load to failure and mechanism of failure of bicortical and unicortical post screws during reduction. Four matched pairs of cadaver legs were subjected to a 2-cm oblique osteotomy simulating a displaced, oblique diaphyseal fracture. A 6-hole compression plate was affixed to the distal fragment with 2 unicortical locking screws, and a 12-mm uni-cortical or 20-mm bicortical screw was inserted as a post screw proximal to the plate. A lamina bone spreader was used to exert a distraction force between the plate and the post screw. A mechanical actuator simulated the distraction procedure until failure. Maximum applied load, displacement, and absorbed energy were recorded and compared across unicortical and bicortical groups by paired t tests. At maximum load, we found statistically significant differences in displacement (P=.003) and energy absorbed (P=.022) between the two groups. All unicortical screws failed through screw toggle and bone cut-out. Bicortical screws failed through bending, with no visible damage to the bone at the screw site. When diaphyseal fractures are significantly shortened and require a greater distraction force to achieve reduction, bicortical screws demonstrate a higher mechanical load to failure and increased bone loss from the screw-removal site. A unicortical post screw may be used if minimal distraction is needed. [Orthopedics. 202x;4x(x):xx-xx.].