Biomechanical comparison of bicortical versus unicortical screw placement of proximal tibia locking plates: a cadaveric model.

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.