Au-delà de la taille de la cage intersomatique : la morphologie du plateau vertébral module la résistance à l'affaissement

Aims: In interbody fusion procedures used to restore disc height and spinal alignment, cage subsidence can compromise correction and stability. Larger cage footprints are generally expected to improve support, but this benefit may depend on how the implant engages the local vertebral endplate surface. This study used a bench-inspired finite element framework to evaluate how endplate morphology and cage length influence resistance to cage subsidence. Material and Methods: The L4 inferior and L5 superior endplates were isolated from a detailed CT-derived lumbar finite element model. Five endplate geometries were then simulated: the native L4 and L5 endplates, a flattened L5 endplate, and L5 endplates with 2- and 3-mm concave pockets. Each geometry was tested with 40-, 50-, and 60-mm interbody cages in a controlled displacement-driven setup. The cage was advanced into the tested endplate at 0.1 mm/s, and force-displacement responses were used to quantify early stiffness and mechanical work to achieve 2 mm of cage penetration. Results: Endplate geometry substantially influenced cage-endplate resistance. Across the 15 configurations, work to 2 mm ranged from 1640 to 2731 N·mm, while stiffness ranged from 1312 to 3230 N/mm. Increasing cage length generally increased resistance, with mean work increasing by 19% and 29% for the 50- and 60-mm cages, respectively, relative to the 40-mm condition. However, this effect depended on endplate geometry, with some models showing limited additional benefit beyond 50 mm, approximately corresponding to the mediolateral diameter of the tested endplates. Conclusion: Under controlled loading, vertebral endplate morphology influenced both cage subsidence resistance and the mechanical benefit of increasing cage length. Significance: These findings suggest that cage footprint alone may not fully characterize mechanical support. Virtual bench testing could help study cage-endplate interactions across different anatomies and support anatomy-informed implant evaluation.