[Safety study of navigation-assisted medial "in-out-in" technique in C₂ screw fixation]

Objective: To evaluate the safety and clinical efficacy of the navigation-assisted medial "in-out-in" technique in C₂ pedicle screw fixation. Methods: This study is a retrospective cohort study. The clinical data of 68 patients with high-riding vertebral arteries of the axis who underwent C₂ pedicle screw implantation using the medial "in-out-in" technique in the Department of Spinal Surgery, Henan Provincial People's Hospital from August 2020 to July 2023 were retrospectively analyzed. There were 32 males and 36 females, with an age of (56.9±10.2) years (range: 35 to 78 years). Among them, 36 patients underwent navigation-assisted medial "in-out-in" technique for C₂ pedicle screw implantation and were included in the navigation group; 32 patients received freehand screw placement and were included in the freehand group. The operative time, intraoperative blood loss, postoperative maximum pedicle-screw distance (PSD_max), bone graft fusion time, fusion rate, and occurrence of internal fixation-related complications were recorded and compared between the two groups. The spinal cord cross-sectional area (SSC) was measured before surgery and at 1 week after surgery. The atlanto-dental interval (ADI), clivus-canal angle (CCA), and Japanese Orthopaedic Association (JOA) score were evaluated before surgery, at 1 week, 3 months, 1 year after surgery, and at the final follow-up. Independent sample t-test, repeated measures analysis of variance, paired t-test, χ² test, or Fisher's exact test were used for data comparison. Results: Six patients with reduction blocked by atlanto-dental osteophytes first underwent anterior cervical atlanto-dental arthroplasty, followed by posterior surgery in the prone position, while the remaining 62 patients underwent posterior reduction and internal fixation. All 36 patients in the navigation group successfully completed C₂ medial "in-out-in" screw implantation, including 34 cases with unilateral medial "in-out-in" screw implantation and 2 cases with bilateral implantation. In the freehand group, 28 cases completed medial "in-out-in" screw implantation, with 4 cases (12.5%) of implantation failure; the implantation failure rate in the navigation group was lower than that in the freehand group (χ²=5.027, P=0.025). The posterior surgical time in the navigation group was shorter than that in the freehand group ((158.1±25.7) minutes vs. (176.4±27.6) minutes, t=2.829, P=0.006), while there was no statistically significant difference in intraoperative blood loss during posterior surgery between the two groups ((217.5±62.2) ml vs. (212.7±53.2) ml, t=0.340, P=0.735). There was no significant change in SSC before and after surgery in both groups (all P>0.05). The postoperative JOA scores, ADI, and CCA in both the navigation group and the freehand group were significantly improved compared with those before surgery (all P<0.01), and there were no differences between the two groups (all P>0.05). The postoperative PSD_max was (4.7±0.9) mm and the bone graft fusion time was (4.9±1.3) months in the navigation group, compared with (4.8±0.5) mm and (4.9±1.7) months in the freehand group, respectively; there were no statistically significant differences between the two groups (all P>0.05). During pedicle preparation, 1 case (2.8%) in the navigation group and 3 cases (9.4%) in the freehand group developed cerebrospinal fluid leakage due to dural puncture by the hand drill. One patient in the freehand group developed symptomatic cerebral infarction postoperatively, presenting with dysarthria, which recovered after medical treatment. There was no significant difference in the incidence of cerebrospinal fluid leakage or vertebral artery injury between the two groups. Conclusion: The navigation-assisted medial "in-out-in" technique enables safe and rapid implantation of three-column fixation screws in patients with high-riding vertebral arteries of the axis, with high accuracy in screw placement and satisfactory clinical outcomes.