Translaminar screw fixation in the subaxial cervical spine: quantitative laminar analysis and feasibility of unilateral and bilateral translaminar virtual screw placement.

Study Design: Morphometric and volumetric analyses and virtual screw placement.
Objective: The aim of the study was to (1) define the morphometric and volumetric dimensions of the laminae of C3-C7 and (2) analyze the feasibility of unilateral and bilateral translaminar screw placement at C3-C7.
Summary of Background Data: Previous studies on translaminar screw fixation have primarily focused on upper cervical and thoracic fixation. Most studies have been conducted on the subaxial cervical vertebrae in the pediatric population and a few in the adult population. In this study, we used computed tomographic (CT) scans to calculate the spatial anatomical environment for translaminar screws at C3-C7. We also determined the feasibility of translaminar screw placement at C3-C7 for clinical applicability.
Methods: Morphometric and volumetric analyses were performed on CT scans of the C3-C7 laminae in 25 male and 25 female patients. A total of 2000 morphometric and 1000 volumetric measurements were performed. The feasibility analysis was performed using unilateral and bilateral virtual screw placement via BrainLAB software (BrainLAB AG, Heimstetten, Germany) on the same CT scans.
Results: Male patients had significantly (P < 0.05) longer translaminar lengths (C5-C7), sagittal-diagonal measurements (C3-C7), and larger volumes (C6-C7) than female patients. Unilaterally, C7 showed 3.5-mm translaminar screw acceptance rates of 100%, C6 showed high acceptance rates (>64%), and C3-C5 showed lower acceptance rates (<52%). C7 accepted bilateral placement at a high rate (96% men, 84% women). C3 and C6 accepted bilateral screws at low placement rates (8%-24%). C4 and C5 never accepted bilateral translaminar screw placement.
Conclusion: Subaxial cervical unilateral translaminar screw placement is a potentially safe and effective technique to use in conjunction with preoperative CT scanning for all vertebral levels. The same is true for bilateral placement at C7 but not at C3-C6. A prospective study to evaluate the long-term outcomes of translaminar fixation at all vertebral levels is currently underway.