A three-dimensional finite element study of the biomechanical changes of cervical spine after 2-level anterior cervical discectomy and fusion with zero-profile system or cage-and-plate fixations

English Keywords:2-level anterior cervical discectomy and fusion  Zero-profile  Cage-and-plate  Middle vertebra  Three-dimensional finite element study

English Abstract:

  【Abstract】 Objectives: To analyze and compare the biomechanical changes after 2-level anterior cervical discectomy and fusion(ACDF) with zero-profile(ZP) system and cage-and-plate(CP) fixations through 3D finite element study. Methods: The CT parameters of C3-C7 of a normal female adult volunteer were collected to develop a finite element model of the cervical spine of C3-C7, and the validity of the model was verified through comparison with previous studies. The surgical segments of both ZP fixation model and CP fixation model were set as C4/5 and C5/6. An axial compression preload of 73.6N was applied over the C3 vertebral body to simulate gravity, and a torque of 1.8N·m was gradually applied to simulate the cervical motions of flexion and extension, lateral bending, and axial rotation. The range of motion(ROM) of the fusion levels, intradiscal stresses of adjacent segments, C5 vertebral body and fusion device stresses were measured and compared between both fixation models. Results: The ROMs of the fused levels of the CP fixation model were all significantly smaller than those of ZP fixation model, respectively, in flexion-extension, lateral bending, and rotation motion states; The intradiscal stress of the adjacent segments (C3/4 and C6/7) of the CP model was much higher than that of ZP model, and the intradiscal stress of the upper vertebra of the fused segments was higher than that of the lower vertebra. In all motion states, the C5 vertebral body stress was all significantly higher in ZP model than that of CP model, which was minimum in flexion (7.36Mpa vs 2.01Mpa); The stresses in the C4/5 and C5/6 intervertebral fusion devices were all greater in ZP model than in CP model. Conclusions: Comparing with CP fixation, ZP fixation in ACDF has smaller limitations to surgical segments, bigger ROM & more micromovements of fusion segements, and greater stress in the fusion device and middle vertebra, which is prone to postoperative cage subsidence or even middle vertebra collapse.