Abstract: BACKGROUND: Anterior cervical discectomy with fusion has become a common procedure in clinical practice. However, the upper and lower radian of the traditional fusion cage is difficult to be consistent with the upper and lower endplates, which is easy to cause a series of complications such as the settlement of the intervertebral fusion cage. Our research group developed a new three-dimensional (3D) printed porous fusion cage that is consistent with the upper and lower endplates.
OBJECTIVE: The mechanical characteristics of the new 3D printed porous fusion cage were evaluated by 3D finite element analysis to provide theoretical basis for clinical application and further improvement. 
METHODS: A 3D finite element model of anterior cervical discectomy with fusion was established. Traditional cervical fusion cage and a new cervical 3D printed porous fusion cage were used for reconstruction. In addition, 50 N preload and 1.0 N•m additional bending moment were applied under six working conditions of forward bending and backward stretching, left and right side bending, left and right rotation. The peak values of vertebral displacement and the peak values of Von-Mises stress on titanium plates, titanium nails, fusion cage, and upper and lower end plates were observed.
RESULTS AND CONCLUSION: (1) Combined with the 3D finite element analysis, we found that the peak values of vertebral displacement and the peak values of Von-Mises stress on fusion cage, upper and lower end plates were significantly lower in the new cervical 3D printed porous fusion cage group than those of the traditional cage group under the six conditions of forward bending, back stretching, left and right side bending and left and right rotation. (2) As for titanium plates and titanium nails, except under the two working conditions of posterior extension and right rotation, the peak value in the new cervical 3D printed porous fusion cage group was larger than in the traditional cage group. Under the other four working conditions, stress peak values were smaller in the new cervical 3D printed porous fusion cage group than in the traditional cage group. (3) Therefore, compared with the traditional fusion cage, the application of the new 3D printed porous intervertebral fusion cage can avoid the stress concentration of upper and lower endplates, improve the stability of fixed segments, and reduce the sinking risk of internal plants to a certain extent.

Key words: three-dimensional finite element analysis, 3D printing, intervertebral fusion cage, internal fixation, displacement, stress, stress concentration, plant sink, stability