Deciphering subsidence risk after ACDF: a biomechanical study on bone density and endplate thickness.

BACKGROUND: Anterior cervical discectomy and fusion (ACDF) is a well-established surgical procedure for restoring neurological function and reconstructing cervical spine alignment. However, postoperative subsidence remains a common complication, and its underlying mechanisms are not yet fully understood. This study aims to investigate the biomechanical effects of varying bone density and endplate thickness on subsidence risk following ACDF. MATERIALS AND METHODS: A validated finite element model of the cervical spine (C2-C7) was used to construct a postoperative single-level ACDF model. Thirteen endplate thicknesses (0.00-0.40 mm), three bone density conditions (normal, osteopenia, osteoporosis), different vertebral bodies and loads (50-150 N) were simulated to assess their effects on von Mises stress distribution and subsidence risk by multivariate linear regression analysis. RESULTS: Both decreased bone density and reduced endplate thickness led to more dispersed stress distribution and increased subsidence risk. Multivariate regression identified endplate thickness as the primary factor affecting stress distribution, while bone density was the primary factor affecting vertebral subsidence. Subgroup analysis found that von Mises stress and subsidence risk exhibited exponential changes when endplate thickness fell below 0.1 mm, particularly in osteoporosis. The subsidence risk in osteoporosis was approximately twice that of normal bone density. Complete endplate loss increased subsidence risk by approximately 1.3 to 1.4 times compared to the intact endplate condition. CONCLUSIONS: Endplate thickness and bone density significantly influence biomechanical stability after ACDF, highlighting the importance of preserving endplate integrity and evaluating bone quality to mitigate the risk of postoperative subsidence.