Feasibility of anterior screw fixation in children: a tomographic study

Feasibility of Anterior Fixation with Single Screw for Odontoid Fractures in Pediatrics: A Computed Tomographic Study

OBJECTIVE

Although it is an effective fixation technique for an unstable odontoid, anterior fixation remains challenging in pediatric populations. Our study measures the anatomical parameters of the odontoid to identify the feasibility of anterior fixation with a single screw for children.

METHODS

We retrospectively collected data from 112 normal male and female children (aged between 2 and 18) in our institute from January 1, 2022 to December 31, 2022. Subjects were divided into a youth group (2-6 years old), a juvenile group (7-12 years old), and an adolescent group (13-18 years old). Sagittal and coronal computed tomography images of the upper cervical spine were used to measure the screw length, angle, and inner and outer diameters of the odontoid. One-way analysis of variance with the Tukey test was used to analyze the parameters among the groups, while the t-test was used to analyze gender differences. Correlations between parameters and age were assessed using Pearson's test.

RESULTS

There were significant differences between male and female subjects in screw length and inner and outer diameters (of both sagittal and coronal views) but not in screw angle. The narrowest diameter of the odontoid was 4.0 ± 1.5 mm in the youth group, 5.5 ± 1.5 mm in the juvenile group, and 5.6 ± 1.1 mm in the adolescent group, respectively. There were significant differences among the three groups in screw length (p < 0.0001). The screw angle of the adolescent group was significantly smaller than that of the youth and juvenile groups. More than 90% of children aged 7-18 years old had an odontoid diameter greater than 4 mm, while only half of the youth group had an odontoid with diameter >4 mm. Screw length and inner and outer diameters in lateral view were positively correlated with age, and screw angle was negatively correlated with age.

CONCLUSION

It is feasible to insert a standard single screw (Φ 3.5 mm) into the odontoid of children aged 7-18 years old but not those aged 2-6 years old. How the anatomical parameters of the odontoid change with age, especially the narrowest diameters, is worthy of attention.

Exploring the micromorphological characteristics of adult lower cervical vertebrae based on micro-computed tomography

We will use micro-computed tomography to scan 31 sets of the adult lower cervical vertebrae (155 vertebrae) to observe the morphological characteristics and direction of trabeculae in the lower cervical vertebrae by outlining and reconstructing the regions of interest and to calculate the variation laws of the microstructure in the regions of interest to reveal their structural characteristics and weak areas. As a result, the images showed that the trabeculae in the lower cervical pedicle near the medial and lateral cortices were relatively dense, and their bone plates were lamellar. There were cavities between the superior and inferior articular processes where the ossification centers had not been absorbed after ossified. The lamellar trabeculae in the vertebral plates near the cortical bones were only 1-2 layers, extended and transformed into rod-shaped trabeculae in a radial shape toward the medullary space. The lamellar trabeculae of the vertebral plate extend over the spinous process near the cortical bone. The statistical results of the trabeculae's morphological parameters showed significant differences in bone volume fraction values among the four parts (P < 0.05). There were substantial differences in BS/BV, except for no differences between the pedicle and the vertebral plate (P < 0.05). There was a significant difference in trabecular pattern factor values between the articular process, the spinous process, and the vertebral plate (P < 0.05) and a significant difference between the pedicle, the spinous process, and the vertebral plate (P < 0.05). There were no significant differences in trabecular bone thickness and trabecular space values among the four parts (P < 0.05). The anatomical microstructural perspective confirms that the optimal choice is internal fixation via the pedicle. If using pedicle screws, the nail tract needs to be placed into the spinous process to increase its holding power and resistance to extraction.

Feasibility analysis of the use of anterior screw fixation in the treatment of pediatric odontoid fracture

BACKGROUND

This study aimed to determine the feasibility of using anterior percutaneous screw fixation to treat odontoid fractures in children of different ages based on computed tomography (CT) measurements.

METHODS

A total of 176 children were enrolled and divided into 3 groups: group A (<6 years of age; 18 males and 22 females), group B (6 to 12 years old; 40 males and 35 females), and group C (12 to 18 years old; 34 males and 27 females). Using 2-dimensional CT reconstruction technology, we measured the children's odontoid parameters, including the coronal external diameter of the base of the odontoid process, the sagittal external diameter of the base of the odontoid process, the length of the odontoid process, the height of the axis vertebral body, and the angle between the axial line of the odontoid process and the vertical line of the anterosuperior border of the C3 vertebral body.

RESULTS

The mean coronal external diameter of the odontoid process base in children under 6 years old was 4.21±1.62 mm, which was not sufficient to accommodate a single screw. Among children aged 6 to 12 years old, this parameter varied widely, and the mean diameter was 5.50±2.80 mm. In the 12- to 18-year-old group, the diameter was 8.64±1.68 mm, which is similar to that of adults. The values of the total height of the axis, and the angle between the axial line of the and the vertical line of the anterosuperior C3 vertebral body border were lower than those for adults.

CONCLUSIONS

The percutaneous odontoid screw fixation technique is not recommended for children under 6 years old. For children aged 6 to 18 years old, this technique is feasible, but individual differences must be considered preoperatively. Selecting the appropriate screw diameter, length, and angle according to the actual CT measurement result is critical.