## 4 Discussion  
In this study, the biomechanical effects of the traditional pedicle screw and CBT screw implant on the lumbar spine were successfully investigated using finite element analysis. Although previous research pointed out that the CBT system can be used in spine revision surgery with reduced blood loss and fixation ability and reduced surgical failure rate [6; 7], there is no biomechanical basis for implantation of the traditional pedicle screw system and the CBT system in the lumbar spine. The results of this study may provide a basis for \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Observation Indicators** & **Motion** & **Group 1** & **Group 2** & **Group 3** & **Group 4** \\ \hline \multirow{4}{*}{Total Deformation (mm)} & Flexion & 3.8823 & 3.6995 & 3.7367 & 3.8419 \\  & Extension & 0.98531 & 0.93348 & 0.94502 & 0.96987 \\  & Lateral Bending & 2.9165 & 2.8883 & 2.8767 & 2.9032 \\  & Axial Rotation & 2.5345 & 2.4754 & 2.5014 & 2.5258 \\ \hline \multirow{4}{*}{Maximum von Mises stress in the lower endplate of L2 (MPa)} & Flexion & 24.198 & 14.136 & 14.318 & 14.781 \\  & Extension & 4.3587 & 2.3782 & 2.4403 & 2.618 \\  & Lateral Bending & 11.249 & 7.1925 & 7.1488 & 7.2184 \\  & Axial Rotation & 10.917 & 6.9309 & 7.0111 & 7.0879 \\ \hline \multirow{4}{*}{Maximum von Mises stress in the upper endplate of L5 (MPa)} & Flexion & 2.8133 & 2.6856 & 2.724 & 2.7806 \\  & Extension & 0.61285 & 0.6596 & 0.64281 & 0.61415 \\  & Lateral Bending & 1.6028 & 1.5632 & 1.5589 & 1.5739 \\  & Axial Rotation & 2.1384 & 2.0675 & 2.1007 & 2.1234 \\ \hline \multirow{4}{*}{Maximum von Mises stress in L2 of the lumbar spine (MPa)} & Flexion & 51.748 & 49.002 & 49.646 & 51.296 \\  & Extension & 24.529 & 24.524 & 24.534 & 24.524 \\  & Lateral Bending & 30.916 & 30.726 & 30.525 & 30.816 \\  & Axial Rotation & 27.205 & 26.735 & 27.06 & 27.373 \\ \hline \multirow{4}{*}{Maximum von Mises stress in L3 of the lumbar spine (MPa)} & Flexion & 387.75 & 117.79 & 360.54 & 133.85 \\  & Extension & 45.282 & 16.088 & 36.571 & 16.114 \\  & Lateral Bending & 174.59 & 74.884 & 162.28 & 73.462 \\  & Axial Rotation & 281.61 & 146.53 & 277.87 & 144.44 \\ \hline \multirow{4}{*}{Maximum von Mises stress in L4 of the lumbar spine (MPa)} & Flexion & 31.918 & 137.22 & 141.65 & 174.75 \\  & Extension & 6.7604 & 13.676 & 11.691 & 15.19 \\  & Lateral Bending & 15.194 & 61.073 & 62.162 & 15.76 \\  & Axial Rotation & 28.869 & 105.49 & 109.36 & 178.67 \\ \hline \multirow{4}{*}{Maximum von Mises stress in L5 of the lumbar spine (MPa)} & Flexion & 22.667 & 22.032 & 22.156 & 22.514 \\  & Extension & 18.48 & 18.371 & 18.4 & 18.434 \\  & Lateral Bending & 31.521 & 31.463 & 31.172 & 31.024 \\  & Axial Rotation & 26.875 & 26.069 & 26.597 & 26.826 \\ \hline \multirow{4}{*}{Maximum von Mises stress on cage (MPa)} & Flexion & 2.2643 & 2.1287 & 2.1078 & 2.1681 \\  & Extension & 0.48433 & 0.38727 & 0.42276 & 0.44886 \\  & Lateral Bending & 1.144 & 1.1426 & 1.1388 & 1.1321 \\  & Axial Rotation & 1.5995 & 1.8331 & 1.7327 & 1.6753 \\ \hline \multirow{4}{*}{Maximum von Mises stress on screw (MPa)} & Flexion & 278.98 & 304.59 & 259.98 & 151.78 \\  & Extension & 41.203 & 33.009 & 43.554 & 35.291 \\  & Lateral Bending & 128.43 & 106.99 & 111.12 & 94.951 \\  & Axial Rotation & 181.69 & 283.02 & 184.61 & 101.42 \\ \hline \multirow{4}{*}{Maximum von Mises stress on cage (MPa)} & Flexion & 35.291 & 156.740 & 77.120 & 44.687 \\  & Extension & 15.342 & 18.377 & 19.979 & 20.651 \\  & Lateral Bending & 32.976 & 44.394 & 47.588 & 45.462 \\  & Axial Rotation & 36.397 & 115.720 & 58.548 & 37.100 \\ \hline \multirow{4}{*}{Maximum von Mises stress on screw (MPa)} & Flexion & 26.592 & 158.63 & 40.654 & 31.28 \\  & Extension & 12.445 & 12.318 & 19.267 & 13.312 \\ \cline{1-1}  & Lateral Bending & 30.308 & 40.019 & 34.393 & 57.484 \\ \cline{1-1}  & Axial Rotation & 39.04 & 122.25 & 44.963 & 162.73 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The values of total deformation on the lumbar spine and the maximum von Mises stress values on the lumbar spine and screw system.