Safe angle scope for posterior atlanto-occipital transarticular screw fixation.

Abstract

To study the technical parameters related to, and explore the clinical significance of, posterior atlanto-occipital transarticular screw fixation. Posterior implantation of Kirschner wires via the atlanto-occipital joint was performed on 20 dry bone specimens with complete atlanto-occipital joints. The angle of the Kirschner wire was measured on a postimplantation x-ray. Three-dimensional computed tomographic reconstruction of the atlanto-occipital joint of 30 healthy adults was performed to measure the simulative safety range for screw placement in posterior atlanto-occipital transarticular screw fixation. The procedure was then conducted on 12 fresh cadaver occipitocervical specimens. X-rays and 3-dimensional computed tomographic reconstruction were performed postsurgery to verify exact screw positioning. The ideal angles for screw placement were cephalocaudal angle in the sagittal plane of 53.3 +/- 3.4 degrees, mediolateral angle in the coronal plane of 20.0 +/- 2.6 degrees, a maximum allowable cephalocaudal angle of 74.6 +/- 2.8 degrees (67.9-80.5 degrees), a minimum allowable cephalocaudal angle of 24.9 +/- 1.9 degrees (22.1-29.4 degrees), a maximum allowable mediolateral angle of 40.5 +/- 2.9 degrees (31.1-49.4 degrees), and a minimum allowable mediolateral angle of 0.7 +/- 1.6 degrees (-4.1-5.9 degrees). Surgery simulation in the fresh cadaver specimens indicated that this safe scope is reliable. There is a safe scope for the angle of the screw placement in posterior atlanto-occipital transarticular screw fixation. Posterior transarticular screw fixation can be safely performed for occipitocervical fusion fixation when utilizing careful screw placement.