Biomechanical Evaluation of Cervical Interbody Fusion Cages for Anterior Cervical Discectomy and Fusion With Variations in Morphology: A Finite Element Analysis.

Abstract

The spinal diseases commonly faced by people in the 19th century included intervertebral disc degeneration, tuberculosis and congenital defects that resulted in neurological impairment and global disability. To address these issues, cervical spine surgery was performed. Modern techniques currently used in spine surgery include interbody devices, pedicle screws, artificial discs and bone grafts. The postoperative complications clinically reported during follow-up include nonunion and implant subsidence, which remain significant drawbacks. The objective of this study is to develop a 3-dimensional finite element model of the C2-C7 cervical spine and validate it against existing experimental studies. The loading conditions considered for this study include a compressive preload of 50 N and a 1 Nm moment applied to the C2 vertebra, with the C7 vertebra fixed at the bottom. In this study, the biomechanical alterations of 4 different cage morphologies were analysed using finite element analysis. Valeo cages with 4 distinct designs were implanted at the C5-C6 level, and physiological motion at the surgical site was studied. Cage subsidence and migration, which can lead to adjacent segment disc degeneration, were also examined. Subsidence was primarily attributed to higher stress encountered in the cage, so stress distribution within the cages was evaluated. Additionally, stress distribution in the anterior plate and screws was analysed. The study concludes that introducing anterior plate and screw fixation helps prevent cage subsidence. Physiological motion at the surgical level was reduced compared to the intact model. Adjacent disc stress was also evaluated and found to be lower than in the intact model.