Biomechanical Effects of Cement Augmentation and Prophylactic Vertebroplasty on Adjacent Segment Stability in Multilevel Spinal Fusion: A Finite Element Analysis

Abstract

Background: Multilevel posterior spinal fusion to T10 often encounters complications such as screw loosening and proximal junctional kyphosis. Cement augmentation or prophylactic vertebroplasty is used to prevent these, but their biomechanical effects remain unclear. Methods: A validated finite element model (T8-pelvis) from CT data of a 57-year-old male was tested in five configurations: fusion only, fusion with cement augmentation at T10, T10-T11, T10-T11 plus T9 vertebroplasty, and T10-T11 plus T8-T9 vertebroplasty. Range of motion (ROM), intradiscal pressure (IDP), posterior ligament/facet stress, and cement-bone interface stresses were analyzed under a 400 N follower load and 10 N<middle dot>m moments. Results: Cement augmentation at the upper instrumented vertebra produced <5% changes in ROM, IDP, and posterior ligament/facet stresses compared with fusion only, indicating preserved stability. Prophylactic vertebroplasty redistributed stress proximally, with elevated cement-bone interface stresses localized at T9 when vertebroplasty was performed at a single adjacent level (T9) and distributed to both T8 and T9 when performed at two adjacent levels (T8-9)-with T9 stressed mainly during lateral bending and extension, and T8 during flexion and lateral bending. Conclusion: Cement augmentation alone did not compromise adjacent-level biomechanics, but prophylactic vertebroplasty created abnormal stress concentrations at adjacent interfaces, potentially increasing fracture risk. These findings highlight the need for careful patient selection and further studies in osteoporotic populations.