Cortical bone trajectory screws placement via pedicle or pedicle rib unit in the pediatric thoracic spine (T9-T12) A 2-dimensional multiplanar reconstruction study using computed tomography

Thoracic cortical bone trajectory (CBT) screw fixation can maximize the thread contact with cortical bone, and it is 53.8% higher than that of the traditional pedicle screws. Moreover, it can also enable less tissue dissection and retraction for reduced muscle disruption. Eighty pediatric patients are divided into 4 age groups and their thoracic vertebrae are analyzed on computed tomography (CT) images. The maximal screw length, maximal screw diameter, screw diameter, and the cephalad angle are measured. The statistical analysis is performed using the Student's t-test and Pearson's correlation analysis. Maximal screw length increases from T9 to T12 and there are significant differences between girls and boys at T9, T10, T11, and T12 in majority of groups (P<0.05). The maximal screw diameter and screw diameter increase from T9 to T12. The maximal screw diameter ranges from 6.27mm to 10.20mm, whereas the screw diameter ranges from 3.87mm to 6.75mm. Meanwhile, the maximum cephalad angle is 23.06 degrees and the minimum is 13.11 degrees. No statistically significant differences in the cephalad angle are found at all levels. Our study establishes the feasibility of 4.5 to 5.5mm CBT screws fixation via pedicle or pedicle rib unit in the pediatric thoracic spine. The entry point of the pediatric thoracic CBT screws is 6 o'clock orientation of the pedicle. Findings of our study also provide insights into the screw insertion angle and screw size decision. Abbreviations: CA = cephalad angle, CBT = cortical bone trajectory, MSD = maximal screw diameter, MSL = maximal screw length, SD = screw diameter.