Anterior transarticular crossing screw fixation for reducible atlantoaxial dislocation with basilar invagination: a radiological feasibility study.

Purpose: The primary focus of surgical treatment for reducible atlantoaxial dislocation with basilar invagination (RADB) is reducing and fixing the atlantoaxial joint. While established anterior, posterior, or combined approaches are effective, they can be associated with significant risks and surgical trauma. Our prior research suggests that anterior transarticular crossing screw (ATCS) fixation via a unilateral anterior cervical minimally invasive approach allows for bilateral screw placement and offers superior stability. However, the anatomical feasibility of ATCS for RADB has not been systematically evaluated. Therefore, this study aimed to radiologically assess the potential trajectories and anatomical feasibility of ATCS fixation in RADB patients.

Methods: A retrospective radiological study was conducted involving 94 patients with RADB, who were categorized into group 1 (with C2-C3 block vertebrae) and group 2 (without C2-C3 block vertebrae). All patients had undergone prior successful reduction and posterior occipitocervical fixation, ensuring a stable post-reduction anatomy for precise measurements. Anatomical parameters for both hypothetical ATCS and anterior transarticular screw (ATS) trajectories were measured from multiplanar computed tomography reconstruction images and flexion-extension radiographs. These included the mandible occlusion angle (MOA), sternum occlusion angle (SOA), screw lateral angles (LAs), screw lengths, screw incline angles (IAs), and screw entry angles on ideal trajectory (EAs). Statistical comparisons were performed to evaluate differences between ATCS and ATS parameters.

Results: In both group 1 and group 2, the MOA of the ATCS was greater than that of the ATS (Group 1: 68.0 ± 12.2° vs. 56.9 ± 10.6°, P < 0.001; Group 2: 61.0 ± 16.4° vs. 57.5 ± 14.7°, P < 0.001), while the SOA of the ATCS was less than that of the ATS (Group 1: -9.8 ± 10.8° vs. -6.3 ± 9.3°, P < 0.001; Group 2: -8.2 ± 13.1° vs. -5.8 ± 12.3°, P < 0.001). Additionally, ATCS demonstrated greater ideal screw lengths (Group 1: 50.5 ± 3.7 mm vs. 24.9 ± 3.0 mm for ATS, P < 0.05; Group 2: 42.4 ± 4.6 mm vs. 27.3 ± 4.1 mm for ATS, P < 0.05) and different angular characteristics compared to ATS. Detailed measurements provided potential optimal screw insertion angles and lengths, indicating radiological feasibility. And the EAs of both ATCS and ATS were between their MOA and SOA.

Conclusions: Anterior transarticular crossing screw placement is radiological feasible for the patients with RADB, especially for the ones with C2-C3 block vertebrae, involving a longer screw.