Transfixion wire positioning within the bone: an option to control proximal tibia external fixation stiffness.

Abstract

The greatest angle that can be formed by the crossing wires at the proximal tibia level without altering safe corridors approaches only 60 degrees. Consequently, the wires are positioned more in the coronal than the sagittal plane. Looking for an increase in sagittal bending stiffness, we evaluated different wire positioning within the proximal tibia and their effect on the stiffness of external fixation of proximal tibia. A fiberglass composite tibia fixed into an idealized ring external frame was tested with a servohydraulic test frame. Load-deformation behavior was compared among the different wire positioning within the proximal tibia under identical conditions of central axial compression, medial compression-bending, posterior compression-bending, posteromedial compression-bending, and torsion. Stiffness values were calculated from the load-deformation and the torque-angle curves. The sample with 3 wires positioned within the bone-2 wires crossed 1 cm posteriorly from the center of the tibia and the third wire placed in coronal plane 1 cm anteriorly from the center of the tibia-was significantly (P < 0.05) stiffer in posterior, posteromedial, and torsional loading configurations compared with all other wire positions within the bone. This new wire positioning within the proximal tibia-2 wires crossed 1 cm posteriorly from the center of the tibia and the third wire placed in coronal plane 1 cm anteriorly from the center of the tibia-increased overall stiffness of external fixation, predominantly in sagittal plane. This work provides a rationale to control proximal tibia external fixation stiffness in sagittal plane.