Biomechanical Effect of C5 /C6 Intervertebral Reconstructive Height on Adjacent Segments in Anterior Cervical Discectomy and Fusion - A Finite Element Analysis.

ABSTRACT

OBJECTIVE: To investigate the biomechanical effect of different intervertebral reconstructive heights on adjacent segments following C5 /C6 anterior cervical discectomy and fusion (ACDF) through finite element analysis. METHODS: A finite element model of intact C4 -C7 segments was developed and validated for the present study. Five additional C4 -C7 postoperative models were constructed with 100%, 125%, 150%, 175%, and 200% of the benchmark height of C5 /C6 on the basis of the intact model. The changes in intradiscal pressure (IDP) and range of motion (ROM) of adjacent segments before and after reconstruction of C5 /C6 were analyzed. RESULTS: For the upper adjacent segment (C4 /C5 ), the IDPs under the different loading conditions all increased after reconstruction. The maximum IDPs were 0.387, 0.489, 0.491, and 0.472 MPa under flexion, extension, axial rotation, and lateral bending, respectively, observed at the reconstructive height of 200%. The minimum IDPs were observed at 150% reconstructive height under all loading conditions except extension, and were 57, 86 and 81% of the maximum IDPs under flexion, axial rotation, and lateral bending, respectively. The minimum IDP under extension occurred when the reconstructive height is 125% of the benchmark height. For the lower adjacent segment (C6 /C7 ), the IDPs of postoperative models under all loading conditions also increased compared to the preoperative model. The maximum IDPs after reconstruction under flexion, extension, axial rotation, and lateral bending were 0.402, 0.411, 0.461, and 0.497 MPa, respectively, when the height of the reconstruction was 200% of the benchmark. The minimum IDPs were observed after a reconstruction at 150% of the benchmark, and were 59%, 85%, 82%, and 81% of the maximum IDPs under flexion, extension, axial rotation, and lateral bending loading conditions. CONCLUSIONS: The reconstructive height is an important factor affecting the IDP and the ROM of adjacent segments after ACDF. To delay the adjacent segment disease, an intervertebral reconstructive height of 150% is an appropriate height in C5 /C6 ACDF.