KINEMATIC EVALUATION OF LUMBAR FUSION TECHNIQUES

Study Design, Eight human cadaveric lumbosacral spines were biomechani cally and kinematically tested in torsion and compression-flexion. The y were retested after simulated posterolateral fusion, anterior lumbar interbody fusion, and circumferential fusion. Objectives. To analyze stiffness and motion in the anterior and posterior columns of the inde x and contiguous spinal motion units of anterior, posterolateral, and circumferential fusions. Summary of Background Data. Previous biomecha nical studies have not incorporated analysis of motion with six degree s of freedom, consideration of contiguous levels, and comparisons of a nterior and posterior column motion. Methods. Eight human cadaveric lu mbosacral spines were biomechanically tested in compression-flexion an d torsion using an advanced biplanar radiography technique. Each speci men underwent either a simulated posterolateral fusion or anterior fus ion followed by a circumferential fusion. Motion and stiffness at the level of the fusion and at contiguous levels were analyzed independent ly in the anterior and posterior columns of the spine. Results. At the level of fusion, the simulated posterolateral and anterior fusions pr evented more motion in torsion compared with compression-flexion. With all specimens, it was shown that circumferential fusions were stiffer than the intact specimen. Our comparison of motion in the anterior an d posterior columns found no significant differences within the column s of a single vertebral motion segment. Compared with posterolateral f usions, anterior fusions were found to have the greatest effect in inc reasing motion at contiguous levels. The effect of circumferential fus ions on adjacent level kinematics was not significantly greater than t hat of anterior fusions. Conclusion. There are major biomechanical dif ferences between different fusion techniques, This information should be considered in patients undergoing lumbar spinal fusion.