Biomechanical comparison of five different atlantoaxial posterior fixationtechniques

Study Design. Five different reconstructions of the atlantoaxial complex we re biomechanically compared in vitro in a nondestructive test. Objectives. To determine whether non-bone graft-dependent one-point fixatio n affords stability levels equivalent to three-point reconstructions. Summary of Background Data. Previous investigations have demonstrated that three-point fixation, using bilateral transarticular screws in combination with posterior wiring, provide the most effective resistance to minimize mo tion around C1-C2. However, placement of transarticular screws is technical ly demanding. Posterior wiring techniques affording one-point fixation have failures of similar to 15%, with failure considered to be secondary to str uctural bone-graft failures. One-point, non-bone graft-dependent fixations have not been tested. Methods. Eight human cervical specimens, C0-C3 were loaded: nondestructivel y, Unconstrained three-dimensional segmental motion was measured. The recon structions tested were two one-point fixations, one two-point fixation; and two three-point fixations. Results. Under axial rotation two and three-point reconstructions provided better stiffness than the one-point reconstructions (P < 0.05), During flex ion-extension, higher stiffness levels were observed in one- and three-poin t fixations when compared with the intact spine (P < 0.05). In lateral bend ing no significant differences were observed among the six groups, although the trend was that reconstructions including transarticular screws provide d greater stability than one-point fixations. Conclusion. The current findings substantiate the use of three-point fixati on as the treatment of choice for C1-C2 instability.