Anterior cervical plate fixation: biomechanical effectiveness as a function of posterior element injury.

OBJECT: The primary goal of this study was to determine if the stabilization provided to the spine by anterior cervical fixation with plating (ACFP) was dependent on the degree of posterior element injury. The secondary goal was to evaluate the effectiveness of additional posterior screw/rod stabilization in these injuries.
METHODS: Following ACFP with interbody bone graft and stepwise transection of the posterior ligaments and facets at C5-6, eight fresh-frozen human C4-7 spine segments were loaded using pure moments of +/- 1.5 Nm in flexion-extension, axial rotation, and lateral bending in the intact state. Posterior screw/rod fixation was performed after complete ligamentous destruction and complete removal of the facets. Repeated-measures analysis of variance and pairwise Student-Newman-Keuls tests were used to detect changes in the range of motion (ROM) and neutral zone (NZ). Statistical significance was assumed at a 95% level. Significant increases in ROM occurred in each loading direction after transection of the capsular ligaments (p < 0.001) and again following facetectomy (p < 0.001) compared with the ACFP condition. Additional posterior fixation resulted in a significant decrease in ROM in all loading directions (p < 0.001). There was a significant increase in NZ for complete ligamentous destruction compared with ACFP (p < 0.05) and facetectomy compared with ACFP (p < 0.05) for flexion-extension. In lateral bending, a significant increase in NZ was found for facetectomy compared with ACFP (p < 0.05).
CONCLUSIONS: Capsular ligaments and articular facets are important structures in limiting three-dimensional vertebral motion in the presence of an anterior plate. Supplementary posterior fixation does reduce motion for all injury conditions.