Introduction: Placement of translaminar screws in the cervical spine has emerged as a useful fixation technique for managing cervical spinal instability. Previous anatomic studies have demonstrated the feasibility of such a procedure at the C2-C7 vertebral levels. Thus far, C1 translaminar screw fixation has received limited attention in the literature. To assess the feasibility of translaminar fixation at the atlas, we have described the dimensions of C1 lamina in the general adult population.
Methods: We retrospectively analyzed 502 consecutive CT scans of the cervical spine performed on patients >18 years of age at a single institution over a 3 month period. C1 laminar diameter, length, height, and trajectory were measured bilaterally. Laminar and screw dimensions were compared to assess instrumentation feasibility.
Results: Average minimum left and right bicortical diameters were 5.62 ± 1.18 mm and 5.58 ± 1.19 mm, respectively. Minimum left and right C1 laminar heights were 10.03 ± 1.72 mm and 10.01 ± 1.74 mm, respectively. Mean left and right C1 laminar lengths were 24.39 ± 2.76 mm and 24.21 ± 2.85 mm, respectively. The average trajectories from midline for left and right laminae were 64.60 ± 4.49 ° and 66.19 ± 4.62 °, respectively. 75.9% of C1 lamina had sufficient bicortical diameter to accept bilateral screw placement. 63.7% of C1 lamina had sufficient height to accept bilateral screw placement.
Conclusions: CT based measurement of atlas morphology revealed that the majority of C1 lamina had sufficient dimensions to accept translaminar screw placement. These findings expand upon previous studies at the C2-C7 vertebral levels by describing the anatomic constraints present at C1. Further study is necessary to assess whether rigid fixation using translaminar screws has comparable fixation strength to more traditional instrumentation methods, such as lateral mass or transarticular screws.
Patient Care: Translaminar screws have been demonstrated to be a useful method of fixation in the subaxial, thoracic and lumbar spine. Translaminar screws may be a useful method for fixation at the atlas in patients who cannot undergo traditional methods of C1 fixation such as lateral mass or transarticular screw placement.
Learning Objectives: By the conclusion of this session, participants should be able to describe the morphology and anatomy of the C1 lamina and be able to identify criteria for feasibility of translaminar screw placement.