Does the Screw Position in the ACDF Affect the Degeneration of Adjacent Segments? A Three-Dimensional Finite Element Analysis

Abstract Background: ACDF is the main treatment of cervical disease. Adjacent Segment Degeneration (ASD) is the main complication of long-term follow-up of ACDF. we conduct a detailed study of ACDF by means of three-dimensional finite element analysis and find the effect of screw placement and location on the occurrence of ASD. Methods: The cervical computed tomography (CT) data (layer thickness of 0.625 mm) for a 30-year-old healthy male volunteer was collected. All the data were combined to create a C2-7 3D finite element model using Abaqus software. Based on the data and the actual surgical maneuver, a screw positioning model was established, in order to observe the cervical range of motion (ROM) with different positions of screw, as well as the pressure change of the adjacent segment intervertebral disc. Results: The proposed finite element model of cervical spine was effective, and ROM on all directions of C4-C6 segments changed after ACDF surgery. Under the same torque settings, compared with the control group, C2/3 segment rotational ROM increased; C2/3, C3/4 segments lateral flexion ROM also increased. Regarding the influence of screw positioning, it has limited influence on the ROM and The intervertebral disc pressure (IDP), and compared with different horizontal positions, different vertical positions imposed greater influence on the ROM and IDP. Conclusions: For ACDF surgery, positioning the screw at the anterior inferior part of the cervical vertebral body could provide more natural cervical ROM and the least IDP, while maintaining high biomechanical stability, and is more in line with human biomechanical requirements.