Comparison of the biomechanical effects of cervical fusion surgery between using a cervical interfacet self-locking cage and a Zero-profile anterior cervical interbody fusion device

English Keywords:Anterior cervical discectomy and fusion  Fusion device  Adjacent segment disease  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To compare the biomechanical effects on the cervical spine between the insertion of a cervical interfacet self-locking cage(CILC) for anterior cervical interbody fusion and the insertion of a Zero-profile anterior cervical interbody fusion device(Zero-P) through the finite element method. Methods: Extracting the thin-layer cervical CT scan data of a 24-year-old male volunteer, and excluding any history of cervical spine trauma, surgery, cervical spondylosis, and imaging-diagnosed cervical spine deformities. Establishing a three-dimensional finite element model(blank model) of the normal lower cervical spine. The validity of the model was verified by comparing the range of motion(ROM) with those reported in previous studies. Based on this model, finite element models were constructed for single-segment posterior CILC insertion and fusion and Zero-P insertion and fusion. The surgical segment was set as the C4/5 segment, and CILC and Zero-P were implanted respectively to fuse and construct model. The lower endplate of the C7 vertebral body was fixed, and an axial load of 73.6N was applied to simulate the head′s weight. A 1.0N·m torque was applied to the upper surface of the C2 vertebral body to simulate the overall movement of the C2-C7 finite element models, including flexion, extension, lateral bending, and axial rotation. The ROM of the segment and the stress changes in the adjacent segment intervertebral discs and facet joints were analyzed in all four motion directions for the blank model, CILC model, and Zero-P model. Results: The ROMs of the established three-dimensional finite element model of the lower cervical spine in all motion directions were consistent with previously published studies, therefore its validity was verified. Compared with the blank model, the ROMs in all directions of the fusion segment was significantly reduced in both the CILC and Zero-P models. The ROM of the adjacent segments and the peak stress in the intervertebral discs and facet joints of the adjacent segments were higher in all motion directions compared with the blank model, with no significant difference in the degree of ROM increase between the CILC and Zero-P models. The peak stress increase in the intervertebral discs of adjacent segments in the CILC model was smaller than that in the Zero-P model. In the CILC model, the peak stress values of the C3/4 segment during flexion, extension, lateral bending, and rotation increased from pre-fixation values of 2.181, 3.358, 3.636, and 3.950MPa to post-fixation values of 2.532, 3.881, 4.463, and 4.917MPa, respectively. The peak stress values of the C5/6 segment during flexion, extension, lateral bending, and rotation increased from pre-fixation values of 1.558, 3.996, 3.778, and 3.660 MPa to post-fixation values of 1.864, 4.131, 4.183, and 4.266MPa, respectively. In the Zero-P model, the peak stress values of the C3/4 segment during flexion, extension, lateral bending, and rotation increased from preoperative values of 2.181, 3.358, 3.636, and 3.950MPa to 2.977, 4.241, 4.654, and 5.509MPa, respectively. The peak stress values of the C5/6 segment during flexion, extension, lateral bending, and rotation increased from pre-fixation values of 1.558, 3.996, 3.778, and 3.660MPa to post-fixation values of 2.314, 5.214, 4.469, and 4.739MPa, respectively. The peak stress increase in the adjacent facet joints in all motion directions was greater in the CILC model than in the Zero-P model. Conclusions: CILC insertion results in less impact on adjacent segment disc stress compared to Zero-P and provides reliable fixation, making it a suitable option for treating adjacent segment disease after cervical surgery.