Biomechanical comparison of two-screw and four-screw zero-profile fusion devices in anterior cervical discectomy and fusion using finite element analysis

Both two-screw and four-screw zero-profile fusion devices are commonly used in anterior cervical discectomy and fusion (ACDF), yet their biomechanical differences remain unclear. This study compared their biomechanical performance using a validated three-dimensional finite element (FE) model of the C2-T1 cervical spine reconstructed from computed tomography data. The devices were implanted at the C5/6 segment to simulate ACDF under various motion conditions. A 75 N follower load and a 1.0 N·m moment were applied to induce flexion, extension, lateral bending, and axial rotation. The two-screw zero-profile device demonstrated higher von Mises stress on the cage and plate but lower stress on the screws than the four-screw device. Stress distributions on the cage, screws, and adjacent vertebral bodies were comparable across models. After fusion, both devices exhibited similar stress characteristics. Overall, the two-screw zero-profile fusion device may achieve biomechanical behavior comparable to that of the four-screw zero-profile fusion device under the investigated static loading scenario. Further long-term clinical and biomechanical investigations are warranted to clarify its biomechanical behavior and potential implications following ACDF.