Biomechanical evaluation of occipitocervical fixation devices

Human cadaveric occipitocervical specimens were implanted with three types of instrumentation The devices were tested biomechanically under three mode s of loading to determine the stiffness of spinal constructs and the failur e mechanisms of the constructs under extreme flexion. The devices tested we re 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 w ere statistically higher than the Luque rectangle in extension and torsion. In extreme flexion, the plate systems failed by fracture of the C2 pedicle s. Modem plate systems, for occipitocervical fixation, provide more stiffne ss and stability than traditional wiring techniques. This study provides su rgeons with information on the relative merits of modern plate and screw sy stems compared with traditional rod and wire constructs.