This numerical simulation study aimed to investigate how the geometric matching between vertebral bony endplates and bone graft affected the segmental biomechanical stability and the risk of cage subsidence following stand-alone lateral lumbar interbody fusion (LLIF), with particular emphasis on the amplifying effect of osteoporosis. Validated finite element (FE) models of the L4–L5 functional spinal unit were constructed under both normal and osteoporotic conditions. A stand-alone LLIF procedure was simulated with varying graft coverage distributed at the superior and inferior endplate–graft interfaces, creating nine distinct matching scenarios. Physiological loads were applied to analyze the segmental range of motion (ROM) and von Mises stress in the bone graft, bony endplate and cage. Inferior graft coverage was the dominant determinant of segmental stability. Increasing inferior coverage from 50% to 75% produced a substantial reduction in ROM, whereas further increasing coverage to 100% exhibited a diminished effect. In contrast, superior graft coverage had a negligible influence on stability. With insufficient inferior coverage (50%), peak endplate stresses reached 57.38 MPa in the normal group and 65.37 MPa in the osteoporotic group, characterized by a pronounced edge-loading pattern. Increasing inferior coverage to 75% markedly alleviated stress concentrations. Peak stresses were consistently observed in lateral bending in both groups. Osteoporosis increased both ROM and stress under insufficient coverage conditions. Using numerical simulations, this study identified inferior graft coverage, with a model-specific biomechanical trend toward an inflection point at approximately 75% in silico, as the core determinant of immediate segmental stability after stand-alone LLIF. Inadequate inferior support induced high-stress edge-loading, especially during lateral bending. Osteoporosis amplified the adverse effects of endplate–graft mismatch.
Ye et al. (Wed,) studied this question.