Biomechanical comparison of anterior instrumentation for the cervical spine

Metal fixation has been advocated to achieve immediate local stabilization during anterior cervical fusion surgery. Screw loosening, screw backout, and breakage of screws or plates remain clinical complications that warrant concern. This study examined the biomechanical characteristics of a prototype anterior cervical plating system with unique screw and plate geometries in comparison to a fixation system currently used clinically. Compared with a standard screw design, a taper screw design resulted in increased ultimate strength and fatigue life. The addition of a locking pin hole in the tapered screw made the screw's fatigue life comparable to the standard design. Pullout strength was comparable in all screw designs. The prototype fixation system had higher strength in pure compression and compression with bending than the comparative system, while also demonstrating improved fatigue characteristics. The tensile bending stiffness of the prototype was double that of the comparative system and within the anatomical range of cervical vertebrae, the bending moment was greater. Torsional yield strength was greater than the reported breaking strength of cervical disc in situ for both systems. The unique designs of the screw and plate geometry resulted in an anterior cervical plate fixation system that is stronger with decreased risk of fatigue failure than a currently used system. Clinical evaluation in patients requiring immediate stabilization is warranted.