Objective 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. Methods CT images (C1-T1) were obtained from a 38-year-old female volunteer. The models of intact C3-7 (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·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. Results The intact model of lower cervical spine (C3-7) 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°, but ROM of C3, 4 and C6, 7 segments increased nearly 5° in both AP and AVB groups. Conclusion As a new reconstruction method of lower cervical spine, AVB fixation provides better stability and lower risk of failure than AP fixation.
Objective To evaluate the effect of polymethylmethacrylate (PMMA) augmentation on cervical stabil ity after anterior cervical interbody fusion (ACIF) before and after fatigue. Methods Twelve porcine cervical spines (C3-7) were subjected to testing angular displacement parameters, including the range of motion (ROM), neutral zone (NZ), and elastic zone (EZ), in nondestructive flexion and extension, right/left lateral bending, and left/right rotation on Motion Analysis motion capture system and MTS-858 servo-hydraul ic testing machine. Intact cervical spines served as control group (group A); oneleveldiscectomy and fusion was performed with anterior plate fixation based on group A as group B; flexion and extension,left/right lateral bending (5 000 cycles) fatigue testing based on group B as group C; the augmentation screw channel was used based on group C as group D; and flexion and extension, left/right lateral bending fatigue testing were performed based on group D as group E. Results The ROM, NZ, and EZ in group A were significantly different from those in other groups (P lt; 0.05) at flexion/extension, left/right bending, and left/right rotation. The ROM, NZ, and EZ in group B were significantly smaller than those in group C (P lt; 0.05) in flexion/extension, left/right bending, and left/right rotation, but there was no significant difference when compared with group D (P gt; 0.05). The ROM and NZ in flexion/extension and the EZ in flexion in group B were significant smaller than those in group E (P lt; 0.05), but there was no significant difference in the other indexes (P gt; 0.05). The ROM, NZ, and EZ in group C in flexion and extension, left/right lateral bending, and left/right rotation were significantly higher than those in groups D and E (P lt; 0.05). The ROM and NZ in flexion and extension and left/right lateral bending, and the ROM in left/right rotation, and the EZ in flexion and extension, right bending, and left/right rotation in group D were significantly smaller than those in group E (P lt; 0.05), but there was no significant difference in the other indexes (P gt; 0.05). Conclusion PMMA augmentation can significantly increase the instant cervical stabil ity and provide a biomechanics basis in cervical anterior plate fixation.