Biomechanical Effect of Different Graft Heights on Adjacent Segment and Graft Segment Following C4/C5 Anterior Cervical Discectomy and Fusion: A Finite Element Analysis

BACKGROUND: The finite element analysis (FEA) was used to explore the effect of different graft heights on adjacent segment and graft segment stress after C4/5 anterior cervical discectomy and fusion (ACDF). MATERIAL/METHODS: A detailed, geometrically accurate 3-dimensional cervical spine model was successfully built from computed tomography (CT) scanning of a healthy adult male. We changed the graft height in C4–C5 to be 90%, 150%, 175%, and 200% of the preoperative disc height and simulated the postoperative scenarios with different bone graft height, respectively. A stress analysis was conducted on the adjacent segment and graft segment. RESULTS: The maximum von Mises stress on C3–C4 showed that when the graft height was 200%, the values were 0.99 MPa, 0.85 MPa, 0.91 MPa, and 0.89 MPa in different loading conditions. For C5–C6, the maximum von Mises stress was 0.77 MPa, 0.83 MPa, 0.91 MPa, and 0.81 MPa, observed when the graft height was 175%, except in extension condition. With regard to graft segment (C4–C5), the biggest von Mises stress was 1.25 MPa, 1.77 MPa, 1.75 MPa, and 1.81 MPa observed at 200% graft height. For these 3 segments, the smallest von Mises stress was found at 150% graft height under the 4 loading conditions. CONCLUSIONS: The graft height makes an important difference on the stress on the adjacent segment and the graft segment after anterior cervical discectomy and fusion. A 150% graft height was considered the proper graft height in C4/C5 ACDF, with the lowest stress on the adjacent segment and the graft segment.