Accuracy of cervical pedicle screw placement with a robotic guidance system via the open midline approach

An increasing number of studies have shown that a robotic guidance system (RGS) can provide accurate cervical pedicle screw (CPS) placement. The accuracy of CPS placement with an RGS has mostly been evaluated according to the magnitude of pedicular cortical violation. However, an RGS assists in pedicle screw (PS) placement by directly indicating the preplanned trajectory in the operative field. Therefore, investigating how accurately the planned trajectory is executed is essential to determine the accuracy of CPS placement using an RGS, in addition to evaluating the clinical accuracy. Hence, this study aimed to evaluate the accuracy of CPS placement using an RGS by comparing the executed trajectory with the planned trajectory.

This prospective study analyzed 174 CPSs placed between C2 and C6 in 39 consecutive patients who underwent cervical fusion surgery using an RGS. The deviation of the executed CPS trajectory from the planned trajectory was measured at the entry point and at a depth of 20 mm in both the axial and sagittal planes on CT images. Additionally, its direction was noted (lateral or medial in the axial plane and cephalad or caudal in the sagittal plane). These measurements were analyzed according to spinal levels (C2 and C3-C6), laterality (right and left sides), and registration material (preoperative and intraoperative CT images). Furthermore, clinical accuracy was assessed using the Neo classification (grades 0-3).

Overall, the mean (± SD) deviations from the planned trajectory at the entry point and at a depth of 20 mm were 0.79 ± 0.65 mm and 0.86 ± 0.69 mm in the axial plane and 0.88 ± 0.81 mm and 0.82 ± 0.79 mm in the sagittal plane, respectively. When separately examining the deviations according to spinal level, laterality, and registration material, the mean deviations were < 1 mm at any point. Analysis of the deviation direction showed that the CPSs were placed divergently from the planned trajectory in the axial plane. In the sagittal plane, the CPSs were likely to be inserted parallel to the planned trajectory. However, at C2 the CPSs were placed in the caudal direction relative to the planned trajectory. Regarding clinical accuracy, the acceptable rates (grades 0 and 1) were 97.7% and 97.1% in the axial and sagittal planes, respectively, without any CPS-related complications.

This study suggests that an RGS can reliably execute planned trajectories, aiding accurate CPS placement in clinical settings.