Surgery for upper cervical spine anomaly instability based on preoperative virtual simulation of screw trajectories / 中华骨科杂志

ABSTRACT

Objective:To evaluate the feasibility of surgery for upper cervical spine anomaly instability achieved by readjusting the clivus-axial angle (CAA) and evaluating available screw trajectories based on preoperative virtual simulation reduction using 3D CT reconstruction.Methods:From January 2014 to September 2019, 52 patients (28 males, 24 females; mean age 46.7 years; range 18-64 years) with upper cervical spine anomalies were enrolled in a retrospective study. DICOM data of preoperative CT scanning of cervical spine were imported into Mimics 15.0 to reconstruct the 3D model of atlantoaxial joint. The target range of CAA was set with the value measured in fusing images of extension view of cervical spine as the upper bound; and 140°, the lower limit of normal CAA range, was set as the lower bound. The trajectories of screws were sought within the target range of CAA. The exact CAA value of the available trajectories was set as the target angle of intraoperative reduction . The preoperative, postoperative and simulated target CAA values were compared. The accuracy of screw placement was evaluated according to the Gertzbein-Robbins scale. The pre- and postoperative neck disability index (NDI) and Nurick scale were also compared.Results:Among 52 patients, available screw trajectories existed in 35 patients. With the validation under computer-assisted navigation as the gold standard, 37 patients underwent Magerl screws fixation (Magerl group) while the other 15 patients underwent screw-rods fixation (screw-rods group). In Magerl group, no significant difference was found between simulated target CAA values (150.1°±6.6°) and postoperative CAA values (149.0°±6.5°)( t=1.194, P=0.240); postoperative CAA values were significantly larger than preoperative CAA values (124.0°±8.9°)( t=-13.499, P< 0.001). In screw-rods group, no significant difference was found between simulated target CAA values (150.4°±5.6°) and postoperative CAA values (150.2°±6.1°) ( t=0.319, P=0.754); postoperative CAA values were also significantly larger than preoperative CAA values (121.9°±8.3°)( t=-12.431, P< 0.001). Follow-up data were obtained in all 52 patients, with a mean follow-up time of 1.7±0.9 years (range, 0.5-4 years). A total of 106 screws were placed into 52 patients, including 74 in Magerl group and 32 in screw-rods group. According to the Gertzbein-Robbins scale, 88 and 15 were classified into grade A and B respectively; and 97.1% (103/106) of screws were acceptable. No severe complications such as vertebral artery injury and low cranial nerve palsy occurred. The postoperative NDI (9.7±6.4 vs. 27.4±8.7) and Nurick scale (1.1±1.4 vs. 2.6±1.3) decreased significantly compared to preoperative ones, respectively. Conclusion:Preoperative virtual simulation can evaluate available screw trajectories and provide the target CAA values for guidance of intraoperative reduction. Based on this, readjusting the CAA under computer-assisted navigation were safe and feasible, and warranted the possibility of a single posterior reduction and fusion approach for reducible upper cervical anomaly instability.