Biomechanical Comparison of Bicortical Versus Unicortical Screw Placement of Proximal Tibia Locking Plates: A Cadaveric Model

Abstract

OBJECTIVE: The purpose of this study was to compare the biomechanical properties of bicortical with unicortical screws in a proximal tibial fracture cadaveric model. SETTING: Biomechanics laboratory at a Level 1 trauma center. PATIENTS/PARTICIPANTS: Eight pairs (4 male and 4 female) of elderly (average age, 79 years; range, 63 to 104 years) cadaveric tibiae. INTERVENTION: Osteotomies were performed in the proximal tibia to reproduce a 41-C2 bicondylar fracture pattern. The 4.5-mm proximal tibial periarticular locking plates (Smith-Nephew, Memphis, TN) were applied to the tibiae with 4 proximal bicortical or unicortical locking screws and 3 screws distal to the fracture site. The fixed tibiae were tested by using a materials testing machine (Instron, Canton, MA) with the axial load on the medial condyle. OUTCOME MEASUREMENTS: The bicortical and unicortical constructs were compared for stiffness, yield load and displacement, and maximum load and displacement to failure. RESULTS: : Bicortical screw placement significantly outperformed unicortical screw placement in stiffness (53.1 +/- 6.7 N/mm versus 35.6 +/- 7.2 N/mm, P < 0.002) and maximum load (476.5 +/- 83.8 N versus 258.9 +/- 62.1 N, P < 0.001) but the yield properties and the ultimate displacement were not significantly different. CONCLUSION: Bicortical screw placement may provide a biomechanically superior construct than unicortical screw placement for the stabilization of unstable proximal tibia fractures.