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

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>or=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.