Graft position versus material in posterior atlantoaxial fusion: establishing a clinical decision hierarchy

BACKGROUND: The optimal bone grafting strategy for posterior atlantoaxial fusion remains controversial, with the interplay between graft position (interlaminar vs. intra-articular) and material (allograft vs. autograft) poorly understood. We aimed to evaluate their interactive effects on clinical and radiographic outcomes. METHODS: In this single-center retrospective cohort study, 52 patients with atlantoaxial instability were categorized into three groups: Group A (n = 18, interlaminar allograft), Group B (n = 19, intra-articular allograft), and Group C (n = 15, intra-articular autograft). Primary outcomes included the Japanese Orthopaedic Association (JOA) score, Neck Disability Index (NDI), Visual Analog Scale (VAS) for neck pain, fusion time, and lateral mass joint space height. Analysis of covariance (ANCOVA) was used to compare final clinical scores, adjusting for baseline values. RESULTS: ANCOVA revealed a significant main effect of group on final JOA (P < 0.001) and NDI (P = 0.003). Both intra-articular groups (B and C) demonstrated significantly better functional outcomes than the interlaminar group (A), with no difference between B and C. VAS improvement was comparable across groups (P = 0.925). Fusion time was shortest in Group C (6.34 ± 0.97 months) versus both Group A (8.83 ± 1.76, P < 0.001) and Group B (8.22 ± 1.27, P = 0.001). Intra-articular allograft achieved greater immediate joint distraction, while autograft better maintained joint height long-term. CONCLUSIONS: In this retrospective cohort study, our findings identify a clear clinical decision hierarchy for posterior atlantoaxial fusion: graft position is the primary determinant of functional outcomes, with intra-articular grafting associated with superior neurological and functional recovery compared to interlaminar grafting. Within the intra-articular space, a material-specific clinical trade-off exists: autograft facilitates faster fusion and better joint height maintenance, while allograft provides comparable mid-term functional outcomes without harvest-site morbidity. These findings suggest that surgical strategy should prioritize intra-articular graft placement when anatomically feasible, with graft material selection individualized to patient factors and surgical priorities.