Ideal entry point and trajectory for C2 pedicle screw placement in children: a 3D computed tomography study.

PURPOSE: To identify the ideal entry point for pediatric C2 pedicle screw and to obtain parameters of it for the indication of pediatric atlantoaxial fusion arthrodesis.

METHODS

The pediatric cervical CT images were reconstructed into the 3D digital models and the C2 vertebrae were separated. The location of ideal entry point and screw placement related linear and angular parameters were assessed on the 3D digital models.

RESULTS

A total of 214 pedicles from 107 C2 digital models were analyzed. The average entry point for C2 was 3.80 ± 2.78 mm medial to the lateral notch (LN) and 2.57 ± 1.70 mm superior to the LN. The average pedicle diameter (PD) was 6.02 ± 1.31 mm, and the average pedicle screw length (PSL) was 25.63 ± 3.46 mm. Statistical differences were found between different sex for PD and PSL (P < 0.05). As patient age increases, using the most lateral and inferior edge of the lateral mass as a reference marker, the entry point tends to move medial and cephalad, when using the LN as a reference marker, the entry point tends to move medial and slightly caudad. Univariate linear regression analysis suggested that these linear parameters were associated with age (P < 0.01).

CONCLUSION

In this study, we found that the measurement results of C2 pedicle screw varied based on sex, laterality, and ages for children younger than 18 years. The entry point of the screws facilitating ideal trajectory tends to change in a linear way as a function of age. This information helps the surgeon to establish the specific anatomy related to C2 pedicle screw placement to facilitate fixation in the pediatric patients.