Study design: Tomographic analysis of occipitocervical (OC) instability in children aged between 2 and 6 years.
Objective: To assess the feasibility of screw placement in various bone anchors in the OC region in young children.
Summary of background data: The use of rigid stabilization in the pediatric patients is gradually increasing. No study has comprehensively assessed the suitability of bony anatomy of the OC region for screw placement, especially in younger children.
Methods: A total of 50 patients (2-6 y, 10 each) who underwent skull and cervical CT scanning were randomly queried using an x-ray database. Screw placement was considered feasible if there was at least 0.5 mm of bone around a 3.5 mm screw through its trajectory. When the bony channel measured 3.5-4.0 mm, placement was considered possible, but difficult.
Results: Statistically, most measures were similar from the right to left sides. External occipital protuberance thickness increased from a mean value of 8.60 mm to a mean value of 10.73 mm. The mean C1 lateral mass length and width varied from 15.26 to 16.67 mm (P=0.056) and 7.34 to 8.58 mm (P=0.0005), respectively, with age. The mean C2 pedicle width and length varied from 3.85 to 4.18 and 17.11 to 19.8 mm, respectively, with age. The mean C2 laminar screw length increased from 20.4 to 22.66 mm with age (P<0.001). C2 lamina widths did not vary much by age. The mean C1-C2 transarticular path length and height increased from 26.7 to 33.6 mm and 2.58 to 3.09 mm, respectively, with age. The width was less directly variable by age (2.68-3.09 mm).
Conclusions: Standard 3.5 mm screws can be used for OC and upper cervical instabilities in children aged between 2 and 6 years. Some anchor points appeared safer compared with others. The occipital keel, C1 lateral mass, and C2 laminae offered adequate space for screw placement in almost all cases. C2 pedicles offered adequate space in 49 sides and barely adequate space in 25 pedicles. Transarticular screws could be safely placed in only 4 of 100 sides. Close radiographic assessment of the vertebral artery course and bony architecture are recommended before surgery in pediatric patients with OC and upper cervical instability.