The feasibility of laminar screw placement in the subaxial spine: analysis using 215 three-dimensional computed tomography scans and simulation software.

BACKGROUND CONTEXT: There have been several reports describing the usage of subaxial cervical laminar screws. However, the anatomic feasibility of placing such screws has not been thoroughly evaluated yet.

PURPOSE: To determine the feasibility of the laminar screw placement in the subaxial cervical spine using a large number of computed tomography (CT) scans and three-dimensional screw trajectory software.

STUDY

DESIGN

Three-dimensional simulation study of screw placement.

PATIENT SAMPLE: Computed tomography scans of 215 consecutive patients were examined, for a total of 430 screws at each level of the subaxial cervical spine.

OUTCOME MEASURES: Successful screw placement without laminar cortical breach, facet joint violation, and collision between two screws in the same level.

METHODS

We simulated the placement of 4.0-mm subaxial (C3-C7) cervical laminar screws. Unilateral and bilateral screw placement was simulated, and their success rates were evaluated at each level of the subaxial cervical spine. This study was not supported by any financial sources. One of the authors received royalties for a posterior cervical fixation system, which is not the topic of this article and is not used or mentioned in this article.

RESULTS

The success rate of unilateral screw placement was the highest at C7 (91.4%), followed by C6 (31.9%), C3 (30.2%), C4 (6.3%), and C5 (4.0%). It was significantly higher (p<.001) in men than in women at C6 and C7 but not at the other levels. The success rate of bilateral screw placement was the highest at C7 (68.8%), followed by C3 (13.5%), C6 (8.8%), C4 (1.9%), and C5 (0.9%). It was significantly higher in men (83.5%) than in women (52.0%) at C7 (p<.001) but not at the other levels.

CONCLUSIONS

The relatively high success rate at C7, particularly of unilateral placement, suggests that laminar screw placement can be a sound alternative method for fixation at this level. However, careful preoperative CT scan evaluation and patient selection are required, particularly for bilateral fixation in women. At C3 and C6, unilateral screw placement can be considered in approximately 30% of patients after careful selection using preoperative CT scans. At C4 and C5, neither unilateral nor bilateral screw fixation is recommended for most patients.