BIOMECHANICAL COMPARISON OF ANTERIOR INSTRUMENTATION FOR THE CERVICAL-SPINE

Metal fixation has been advocated to achieve immediate local stabiliza tion during anterior cervical fusion surgery. Screw loosening, screw b ackout, and breakage of screws or plates remain clinical complications that warrant concern. This study examined the biomechanical character istics of a prototype anterior cervical plating system with unique scr ew and plate geometries in comparison to a fixation system currently u sed clinically. Compared with a standard screw design, a taper screw d esign resulted in increased ultimate strength and fatigue life. The ad dition of a locking pin hole in the tapered screw made the screw's fat igue life comparable to the standard design. Pullout strength was comp arable in all screw designs. The prototype fixation system had higher strength in pure compression and compression with bending than the com parative system, while also demonstrating improved fatigue characteris tics. The tensile bending stiffness of the prototype was double that o f the comparative system and within the anatomical range of cervical v ertebrae, 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 r esulted 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 w arranted.