Computed tomography morphometric analysis for axial and subaxial translaminar screw placement in the pediatric cervical spine

Clinical article

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Object

The management of upper cervical spinal instability in children continues to represent a technical challenge. Traditionally, a number of wiring techniques followed by halo orthosis have been applied; however, they have been associated with a high rate of nonunion and poor tolerance for the halo. Alternatively, C1–2 transarticular screws and C-2 pars/pedicle screws allow more rigid fixation, but their placement is technically demanding and associated with vertebral artery injuries. Recently, C-2 translaminar screws have been added to the armamentarium of the pediatric spine surgeon as a technically simple and biomechanically efficient means of fixation. However, the use of subaxial translaminar screws have not been described in the general pediatric population. There are no published data that describe the anatomical considerations and potential limitations of this technique in the pediatric population.

Methods

The cervical vertebrae of 69 pediatric patients were studied on CT scans. Laminar height and thickness were measured. Statistical analysis was performed using unpaired Student t-tests (p < 0.05) and linear regression analysis.

Results

The mean laminar heights at C-2, C-3, C-4, C-5, C-6, and C-7, respectively, were 9.76 ± 2.22 mm, 8.22 ± 2.24 mm, 8.09 ± 2.38 mm, 8.51 ± 2.34 mm, 9.30 ± 2.54 mm, and 11.65 ± 2.65 mm. Mean laminar thickness at C-2, C-3, C-4, C-5, C-6, and C-7, respectively, were 5.07 ± 1.07 mm, 2.67 ± 0.79 mm, 2.18 ± 0.73 mm, 2.04 ± 0.60 mm, 2.52 ± 0.66 mm, and 3.84 ± 0.96 mm. In 50.7% of C-2 laminae, the anatomy could accept at least 1 translaminar screw (laminar thickness ≥ 4 mm).

Conclusions

Overall, the anatomy in 30.4% of patients younger than 16 years old could accept bilateral C-2 translaminar screws. However, the anatomy of the subaxial cervical spine only rarely could accept translaminar screws. This study establishes anatomical guidelines to allow for accurate and safe screw selection and insertion. Preoperative planning with thin-cut CT and sagittal reconstruction is essential for safe screw placement using this technique.

Article Information

Address correspondence to: Andrew Jea, M.D., Division of Pediatric Neurosurgery, Department of Neurosurgery, Texas Children's Hospital, Baylor College of Medicine, 6621 Fannin Street, CCC 1230.01, Houston, Texas 77030. email: ajea@bcm.tmc.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Measurement of the pediatric cervical spine. A: Parasagittal reconstruction of CT scan showing the height, or cranial-caudal dimension, of the laminae. B: Axial CT scan showing the laminar thickness at its isthmus.

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    Axial CT scan showing the C-2 laminae with crossing translaminar screws.

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    Graphs plotting laminar height (A–F) and thickness (G–L) against age at each cervical level. (See Results for the estimated growth rates.) A trend toward increase in height with increase in patient age was observed in all levels. In contrast, the laminar thickness changed minimally in the studied ages. Note that at the C3–6 levels, most of the laminar thickness measurement fell under the 4.5 mm threshold.

  • View in gallery

    Graphs plotting laminar height (upper) and thickness (lower) against cervical levels from C-2 through C-7 for all patients in the study population. The laminar height threshold for bilateral translaminar screw placement is defined at 9 mm; the thickness threshold, 4.5 mm.

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    Graphs plotting laminar height (upper) and thickness (lower) against cervical level with patients stratified by sex. The differences between male and female patients in both laminar height and thickness were not statistically significant.

  • View in gallery

    Graphs plotting laminar height (upper) and thickness (lower) against cervical level with patients stratified by age (< 8 years and ≥ 8 years). The differences in laminar height in the 2 age groups were statistically significant in all levels. The differences in laminar thickness were not significant except at C-7.

  • View in gallery

    Graph showing the distribution of patients whose anatomy was able to accept bilateral translaminar screws at the C-2 level. In 21 (30.4%) of 69 patients the anatomy could accept bilateral C-2 screws (bilateral laminar height ≥ 9 mm and laminar thickness ≥ 4.5 mm). In only 9.4% of patients (3 of 32) who were younger than 8 years old could the anatomy accept bilateral C-2 screws. In contrast, in 48.6% of patients (18 of 37) who were at least 8 years old bilateral C-2 translaminar screws could be accommodated. No = bilateral C-2 laminar screws could not be accommodated; Yes = bilateral C-2 translaminar screws could be accommodated.

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