Study design: This is a cadaver specimen study to confirm new pedicle screw (PS) entry point and trajectory for subaxial cervical PS insertion.
Objective: To assess the accuracy of the lateral vertebral notch-referred PS insertion technique in subaxial cervical spine in cadaver cervical spine.
Backgrounds: Reported morphometric landmarks used to guide the surgeon in PS insertion show significant variability. In the previous study, we proposed a new technique (as called "notch-referred" technique) primarily based on coronal multiplane reconstruction images (CMRI) and cortical integrity after PS insertion in cadavers. However, the PS position in cadaveric cervical segment was not confirmed radiologically. Therefore, the difference between the pedicle trajectory and the PS trajectory using the notch-referred technique needs to be illuminated.
Methods: Twelve cadaveric cervical spines were conducted with PS insertion using the lateral vertebral notch-referred technique. The guideline for entry point and trajectory for each vertebra was established based on the morphometric data from our previous study. After 3.5-mm diameter screw insertion, each vertebra was dissected and inspected for pedicle trajectory by CT scan. The pedicle trajectory and PS trajectory were measured and compared in axial plane. The perforation rate was assessed radiologically and was graded from ideal to unacceptable: Grade 0 = screw in pedicle; Grade I = perforation of pedicle wall less than one-fourth of the screw diameter; Grade II = perforation more than one-fourth of the screw diameter but less than one-second; Grade III = perforation more than one-second outside of the screw diameter. In addition, pedicle width between the acceptable and unacceptable screws was compared.
Results: A total of 120 pedicle screws were inserted. The perforation rate of pedicle screws was 78.3% in grade 0 (excellent PS position), 10.0% in grade I (good PS position), 8.3% in grade II (fair PS position), and 3.3% in grade III (poor PS position). The overall accepted accuracy of pedicle screws was 96.7% (Grade 0 + Grade I + Grade II), and only 3.3% had critical breach. There was no statistical difference between the pedicle trajectory and PS trajectory (p > 0.05). Compared to the pedicle width (4.4 ± 0.7 mm) in acceptably inserted screw, the unacceptably screw is 3.2 ± 0.3 mm which was statistically different (p < 0.05).
Conclusion: The accuracy of the notch-referred PS insertion in cadaveric subaxial cervical spine is satisfactory.
Keywords: Cadaver study; Lateral vertebral notch; Pedicle mediolateral angle; Pedicle screw trajectory; Subaxial cervical spine.