Biomechanical Comparison of Optimal Shapes for the Cervical Intervertebral Fusion Cage for C5-C6 Cervical Fusion Using the Anterior Cervical Plate and Cage (ACPC) Fixation System: A Finite Element Analysis.

BACKGROUND The fifth and sixth cervical vertebrae (C5-C6) represent the high-risk segment requiring surgical correction in cervical spondylosis. Anterior cervical discectomy and fusion (ACDF) of C5-C6 includes an intervertebral fusion cage to maintain foraminal height and is combined with anterior plate fixation. The shape of the intervertebral cage can affect the postoperative outcome, including the rates of fusion, subsidence, and neck pain. This study aimed to use finite element (FE) parametric analysis to compare biomechanical properties of changes in intervertebral cage shape for C5-C6 cervical fusion using the anterior cervical plate and cage (ACPC) fixation system. MATERIAL AND METHODS Five shapes were designed for cervical intervertebral cages, square, oval, kidney-shaped, clover-shaped, and 12-leaf-shaped. The performance was evaluated following implantation into the validated normal C5-C6 FE model using simulation with five physiological conditions. The indicators included the maximum von Mises stress of the endplates, the fusion cages, and the cervical vertebrae. The postoperative subsidence-resistance properties were determined, including the interior stress responses of the intervertebral cages and the surrounding tissues. The fusion-promoting properties were evaluated by the interior stress responses of the bone grafts. RESULTS The optimal shape of the cervical intervertebral cage was the 12-leaf-shape for postoperative subsidence resistance. The kidney shape for the cervical intervertebral cage was optimal for postoperative fusion. CONCLUSIONS FE analysis identified the optimal cervical intervertebral cage design for ACPC fixation of C5-C6. This method may be useful for future developments in the design of spinal implants.