Finite Element Analysis of the Effect of Dynamic Plating on Two-Level Anterior Cervical Discectomy Fusion Biomechanics.

ABSTRACT

BACKGROUND: The limitations of anterior cervical discectomy and fusion (ACDF) are related to mechanical failure of the construct after recurring subsidence and migration. In the present study, we evaluated the effect of the maximum rotation of variable angle screws on the range of motion (ROM), cage migration, and subsidence. METHODS: Five finite element models were developed from a C2-C7 cervical spine model. The first model was an intact C2-C7 spine model, and the second model was an altered C2-C7 model with C4-C6 cage insertion and a 2-level static plate. The other three models were altered C2-C7 models with the same C4-C6 cage insertion and a 2-level dynamic plate. RESULTS: The ROM of C4-C6 in the static plate model was reduced by ∼14° from the intact model but only reduced by ∼9° in the dynamic plate models. The maximum migration and subsidence at the cage-endplate interface in the dynamic plate models were lower than those in the static plate model for all moments. The von Mises stress of the C3-C4 and C6-C7 discs in the dynamic plate models was lower than that in the static plate model. CONCLUSIONS: Our results indicate that dynamic plating has promising potential (greater ROM and lower von Mises stress of discs) for stabilization in multilevel anterior cervical discectomy and fusion than static plating, although both dynamic and static plates showed lower ROM than the intact model. A lower screw rotational angle resulted in superior biomechanical performance (lower incidence of migration and subsidence) compared with a higher rotational angle in multilevel applications, regardless of loading.