Associate Professor University of Minnesota Department of Orthopedic Surgery Minneapolis, Minnesota, United States
Introduction: Cervical pedicle screws (CPS) are biomechanically superior to other spinal fixation anchors; but placement is technically demanding, and malposition can have catastrophic consequences. Computer navigation (CN) has been shown to improve accuracy rates in thoracolumbar pedicle screw placement. However, there are limited studies on use of CN for placing CPS. We report accuracy rates of CN subaxial (C3-C7) CPS placement at a single institution.
Methods: We reviewed patients from 1/2014-3/2020 who underwent CN CPS placement with either postoperative computed tomography (CT) or intraoperative O-arm 3D scan for screw evaluation. CPS position was evaluated in axial, coronal and sagittal planes, and graded as shown in figure 1. Demographic data was collected and statistical analyses completed.
Results: 413 CN CPS were placed in 100 patients (54M:46F), with a mean age of 56 years (range 10-81). Number of fusion levels ranged from 1-12. 44 patients had previous cervical spine fusion (29 anterior; 15 posterior). 12 patients underwent proximal extension of previous thoracolumbar fusion. Rates of serious screw malpositions were 3.6% (Gr III) and 10.2% (combined Gr II/III). A breakdown of screws can be seen in figure 1. Mean screw grade per level: C3=0.88, C4=0.67, C5=0.51, C6=0.46, C7=0.26. Using non-parametric ranksum tests with Bonferroni correction, significant differences were noted between the following: C3 vs C6 and C7 (p = 0.029 and < 0.001, respectively) and C7 vs C3 and C4 (p = 0.029 and < 0.001, respectively).
Conclusion : We found a 3.6% rate of dangerous (Gr III) and 10.2% non-ideal (Gr II/III) CPS placement using intraoperative 3D imaging and CN. Mean screw grade decreased caudally, indicating pedicle breach is more likely at the upper levels. This also confirms C7 is the safest level for CPS placement. Our results add to only few other studies that have reported on this technique. To our knowledge this is the biggest study on a uniform technique of CN subaxial CPS placement.
