The Feasibility Study Of Atlanto-axial Transarticular Fixation In Children Using Multipanar Reconstruction Of Helical Computed Tomography

Objectives: The aims of this study were to observe and measure the correlate coefficient of pediatric C1C2 and atlanto-axial transarticular screw fixation, to investigate the influence factors of appropriate placement of screws, and to evaluate the capability of 3.5mm screw trajectory in bone dimensions within different age groups of children, to prevent complications and improve the safety during operation.Methods: The 3D images were observed on CT taken from 80 children objects, whom were equally divided into 4 age groups. Group 1 aged from 0-2 years, group 2 aged from 2-4 years, group 3 aged from 4-8 years, and group 4 aged from 8-12 years. The bilateral isthmus widths and heights, distances between optimal screw path and artery groove, optimal screw lengths, medial angles and sagittal angles were measured in the appropriate oblique axial planes and oblique parasagittal planes by using 3D reconstruction of the image on CT workstation. SPSS10.0 was used for statistical analysis. The Least—significant difference(LSD) t test was applied to the comparisons within groups.Results: (1) 160 CT images taken on the oblique parasagittal planes were observed. Type I vertebral artery groove contributed to 76.25%, type II contributed to 6.25%, type III contributed to 12.5%, and type IV contributed to 5%. (2) Significant statistical differences within groups were found in the bilateral linear parameters—isthmus width and height and optimal screw length, which were the indicators of bone development. No significant statistical difference within groups was found in the linear parameter—the distance between optimal screw path and artery groove, which was the indicator of variance of vertebral artery groove. No significant statistical difference found in angular parameters. (3) The acceptance rates of screws on at least one side in group 1 was respectively 15% and 40% according to criteria 1 and 2. The criteria 1 was set as both isthmus width and height were greater than 5mm, and the distance between optimal screw path and vertebral artery groove was greater than 2.5mm. The criteria 2 was set as both isthmus width and height were greater than 4.5mm, and the distance between optimal screw path and artery groove was greater than 2.5mm. The acceptance rates in group 2 were 55% and 85%, the rates in group 3 were 85% and 95%, and the rates in group 4 were 90% and 90%. The youngest margin age of being capable of placing screws was 1 year old according to criteria 1, but the age was only 9 months according to criteria 2.Conclusions: The distance between OSP and VAG could provide better evaluation of the influence that the vertebral artery groove variation had on the atlanto-axial transarticular screws fixation. (1) The isthmus width and height and optimal screw length were increasing with age. The vertebral artery groove variation and angles of placing screw had no relationship with age. (2) The average medial angle and sagittal angle were about 10°and 40°respectively, and that could be used as reference values. (3) Most of the children aged over 4 years could accept the 3.5mm transarticular screw on at least one side. (4) The individual variance should be considered before operation. Doctors should have efficient imageology data analyzed, be aware of the variations on C2 pedicle and vertebral artery groove, adjust the plan, and achieve the individualized operations.