Evaluation of axis vertebrae for optimal screw placement in craniovertebral junction surgeries: A morphometric study on dry bone

Background: Surgeries in the craniovertebral junction (CVJ) area require precise anatomical knowledge of every component to deal with disorders of the CVJ. The present study aimed to measure the dimensions and angles of the axis vertebrae and to establish the clinical correlations of neurosurgical significance. Materials and Methods: We analyzed 140 axis vertebrae and measured the lamina, pars interarticularis, pedicle, and the angle of the C2 pedicle screw, which was done bilaterally with the help of a digital Vernier caliper and goniometer. All measurements were taken in millimeters (mm). The observations were analyzed statistically to recognize various trends and variations in the axis vertebrae. The P > 0.05 was taken as insignificant differences of the measured values. Results: The optimal length of screw to be placed in the lamina was 23.57 ± 0.24 and 23.56 ± 0.24 on the right and left sides, respectively, whereas the thickness came out to be 4.46 ± 0.35 and 4.45 ± 0.36 for the respective sides. Pars length was measured 14.99 ± 1.31 on the right and 14.85 ± 1.28 on the left side. The pedicle length for the screw placement was 27.30 ± 0.86 and 27.22 ± 1.00 on the right and left sides, respectively, whereas the pedicle thickness was 6.84 ± 0.91 on the right and 6.83 ± 0.92 on the left side. The appropriate angle which is needed to put a pedicle screw in C2 was 28.04° ±2.37° and 28.13° ±2.33° on the respective sides, right and left. Conclusions: The study presents a comprehensive idea for standard screw fixation by studying the morphometry of the axis vertebrae in human dry bones. The approximate size of the screw and the angle needed in case of C2 vertebra fixation are ascertained in this study. The detailed measurements provide insight into helping neurosurgeons to optimize the presurgical planning in CVJ surgeries.