Biomechanical evaluation of occipitocervical fixation devices

Human cadaveric occipitocervical specimens were implanted with three types of instrumentation. The devices were tested biomechanically under three modes of loading to determine the stiffness of spinal constructs and the failure mechanisms of the constructs under extreme flexion. The devices tested were the AXIS Fixation System (with custom plate), the Y-Plate, and the Luque rectangle. No significant differences in stiffness among the devices were found under compression and flexion. The stiffnesses of the plate systems were statistically higher than the Luque rectangle in extension and torsion. In extreme flexion, the plate systems failed by fracture of the C2 pedicles. Modern plate systems, for occipitocervical fixation, provide more stiffness and stability than traditional wiring techniques. This study provides surgeons with information on the relative merits of modern plate and screw systems compared with traditional rod and wire constructs.