Reducibility-Based Posterior Reduction and Fusion Strategies for Atlantoaxial Dislocation: A Clinical and Radiological Study

Objective: This study aims to evaluate the clinical and radiological outcomes of posterior reduction and fusion strategies, with or without interfacet joints distraction and cage implantation, based on reducibility, in the surgical management of atlantoaxial dislocation (AAD). Methods: Patients who underwent posterior reduction and fusion surgery for AAD in our institution were included. They were categorized into 2 groups based on reducibility. Japanese Orthopaedic Association (JOA), visual analogue scale (VAS), and patient-reported satisfaction scores were collected. The atlantodental interval, distance of the tip of the odontoid to Chamberlain's line (DOCL), clivus-axial angle (CXA) and mean obliquity of the atlantoaxial articular facet (OAAF) were measured on computed tomography (CT) images. Fusion was evaluated using CT and dynamic x-rays. Results: A total of 90 patients (45 males and 45 females) were included. Among them, 54 patients in the reducible group underwent direct posterior reduction and fusion, and 36 patients in the irreducible group were treated with additional interfacet joint distraction and cage implantation. All patients showed significant improvements in JOA and VAS scores postoperatively. In the irreducible group, the preoperative CXA was smaller, whereas the OAAF was greater. Receiver operating characteristic curve analysis identified optimal cutoff value of OAAF in predicting reducibility was 32.4° (sensitivity: 86.1%, specificity: 81.5%). Postoperative changes in DOCL and CXA were more pronounced in irreducible group. The fusion rates were comparable in the 2 groups (92.6% vs. 94.4%, p=0.730). Conclusion: The reducibility-based posterior reduction fusion strategy achieves satisfactory clinical and radiological outcomes in the surgical management of AAD. For reducible cases, direct reduction under continuous intraoperative skull traction is preferred to minimize surgical trauma. In contrast, interfacet joints distraction and cage implantation are essential for irreducible cases. Preoperative OAAF may act as a potential predictor of reducibility.