[Finite element study on anterior transpedicular screw-artificial vertebral body fixation in lower cervical spine]

To compare the biomechanical properties of the anterior transpedicular screw-artificial vertebral body (AVB) and conventional anterior screw plate system (AP) in lower cervical spine by finite element study.

CT images (C1-T1) were obtained from a 38-year-old female volunteer. The models of intact C(3-7) (intact group), AP fixation (AP group), and AVB fixation (AVB group) were established and analyzed by Mimics 14.0, Geomagic Studio 2013, and ANSYS 14.0 softwares. The axial force of 74 N and moment couple of 1 N x m were loaded on the upper surface and upper facet joint surfaces of C3. Under conditions of flexion, extension, lateral bending, and rotation, the Von Mises stress distribution regularity and maximum equivalent stree of AP and AVB groups were recorded, and the range of motion (ROM) was also analyzed of 3 groups.

The intact model of lower cervical spine (C(3-7)) was established, consisting of 286,382 elements and 414,522 nodes, and it was successfully validated with the previously reported cadaveric experimental data of Panjabi and Kallemeyn. The stress concentrated on the connection between plate and screw in AP group, while it distributed evenly in AVB group. Between AP and AVB groups, there was significant difference in maximum equivalent stress values under conditions of 74 N axial force, flexion, extension, and rotation. AVB group had smaller ROM of fixed segments and larger ROM of adjacent segments than AP group. Compared with intact group, whole ROM of the lower cervical spine decreased about 3 degrees, but ROM of C(3,4) and C(6,7) segments increased nearly 5 degrees in both AP and AVB groups.

As a new reconstruction method of lower cervical spine, AVB fixation provides better stability and lower risk of failure than AP fixation.