Image measurements of os odontoideum in children

BACKGROUND: Conservative therapy is used for children with odontoid fracture; however, when the odontoid fracture is complicated by significant displacement and unstable, surgery is required. Anterior cervical hollow lag screw fixation has been successfully used in adult patients, but until now, there has not been any relevant image measurement research in children with os odontoideum. The aim of the present study was to identify the morphometric changes of normal os odontoideum in children of different ages and to discuss parameters for screw fixation. METHODS: Computed tomography (CT) scanning data of normal os odontoideum in 120 children of different ages were measured. The parameters were as follows: transverse and vertical diameters of cancellous bone and cortical bone in os odontoideum basilar part, angle and distance from simulation screw insertion point (anterior mid-point of C2 vertebral body) to os odontoideum anterior angle as well as posterior angle, the optimal insertion angle, and the optimal screw length. RESULTS: The basilar part of normal os odontoideum was roughly round, and vertical diameter was slightly larger than transverse diameter. All parameters measured in the present study increased with age. The safety screw insertion angle range was 16–36°, and the optimal insertion angle ranged from 19° to 22°. The safety screw path length ranges in the 3–5-, 6–9-, and 10–14-year groups were 8–14, 10–16, and 12–21 mm, respectively, and the optimal screw length ranges were 13–14, 15–16, and 19–20 mm, respectively. The height of the axis showed a growing dimension followed by the advancing age in all groups. In each group, the height of the axis of the male is greater than the female. CONCLUSIONS: For children undergoing odontoid screw fixation for the treatment of type II odontoid fracture, it is important to select the appropriate screw diameter, length, and direction according to parameter changes of os odontoideum based on their age.