Abstract: BACKGROUND: The core of anterior decompression is to relieve the compression of spinal cord and nerve and restore the intervertebral height and physiological curvature of cervical spine. However, the cage currently used in the clinic cannot satisfy the individualized needs, resulting in the destruction of the endplate of the fusion segment and the subsidence or displacement of the cage. In this study, a height adjustable cervical fusion cage was designed, which can be implanted into the intervertebral space to fit with the upper and lower end plates of the intervertebral space.  
OBJECTIVE: To evaluate the mechanical characteristics of the new height adjustable cervical fusion cage by three-dimensional finite element analysis, and to provide corresponding theoretical basis for clinical application and further improvement.
METHODS:  The three-dimensional finite element models of anterior cervical discectomy and fusion were established and the models were divided into normal group, lower cage implantation height group, moderate cage implantation height group and higher cage implantation height group. 50 N preload and 1.0 N·M motion additional bending moment were applied under six working conditions of flexion and extension, left and right lateral flexion and left and right rotation. The corresponding peak Von Mises stress of vertebral body, peak Von Mises stress of cage, intervertebral disc stress and C3-C7 vertebral motion range were observed.  
RESULTS AND CONCLUSION: (1) The peak Von Mises stress of fusion cage and the peak Von Mises stress of C3-C7 vertebral body in the group with moderate cage implantation height were lower than those in the group with lower cage implantation height and the group with higher cage implantation height. (2) The stress difference of C4/5 intervertebral disc was obvious after implantation of different height cages. (3) The overall intervertebral relative activity of C3-C7 decreased the most in the higher cage implantation height group, followed by the moderate cage implantation height group, and the overall intervertebral activity decreased least in the lower cage implantation height group. (4) It is suggested that the appropriate implantation height of the cage can make the cervical spine achieve immediate stability, and minimize the stress on the cage and cervical vertebra, so as to effectively avoid the cervical cage subsidence.

Key words: three-dimensional finite element analysis, cervical cage, height adjustable, stress concentration, biomechanics