Posterior atlantoaxial fixation: biomechanical in vitro comparison of six different techniques.

STUDY DESIGN: Six different techniques for atlantoaxial fixation were biomechanically compared in vitro by nondestructive testing.

OBJECTIVE: To evaluate the immediate three-dimensional stability of a new atlas claw combined with transarticular screws and alternative techniques for transarticular screw fixation in comparison with established techniques.

SUMMARY OF BACKGROUND DATA: Posterior transarticular screw fixation in combination with wire-bone graft constructs is frequently used for C1-C2 fixation. Sublaminar wire passage carries the potential risk of neurologic complication. Transarticular screw fixation is technically demanding and, for anatomic reasons, not always feasible.

METHODS: Six human cervical specimens were loaded nondestructively with pure moments, and unconstrained motion at C1-C2 was measured. The six specimens were instrumented with each of the following fixation techniques: Gallie fixation, transarticular screws and Gallie fixation, transarticular screws, transarticular screws and a new atlas claw, isthmic screws in the axis and the atlas claw, and lateral mass screws in the atlas and isthmic screws in the axis connected with rods.

RESULTS: The transarticular screws restricted lateral bending and axial rotation best. The three-point fixations (transarticular + Gallie and transarticular + claw) additionally restricted flexion-extension, with lowest values for transarticular screws and the atlas claw. The alternative techniques were not as stable as the three-point fixations, but more stable than the Gallie fixation.

CONCLUSIONS: Biomechanically, the three-point fixation with transarticular screws and the atlas claw provides a rigid internal fixation that is not dependent on bone graft and sublaminar wiring. In cases wherein transarticular screws are not feasible, the isthmic screws and claw or the lateral mass screws and isthmic screws are biomechanical alternatives with less immediate stability.