## 3 Results
### Lateral Bending and Rotation  
In lateral bending, the differences between the three FE models in terms of the ROM and stiffness at adjacent level L2-L3 were within 5% (Table 4). In disc stress distributions, these FE models exhibited similar patterns, as displayed in Figure 8. In rotation, the ROM increased by 28% and 16% in the DEF and NIPD models, respectively, compared with the INT model. In the disc stress and facet joint, only minor changes were noted in the FE models (Table 5). Moreover, the change in the facet joint force in rotation and lateral bending was within 5 N in all three models.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **INT** & **DEF** & **NIPD** \\  & **Moment: 4.5 Nm** & **Moment: 4.5 Nm** & **Moment: 5.1 Nm** \\ \hline \multicolumn{4}{c}{**ROM (degree)**} \\ \hline L1–L2 & 2.12 & 2.12 & 2.29 \\ L2–L3 & 1.76 (100\%) & 1.79 (102\%) & 1.91 (109\%) \\ L3–L4 & 1.37 (100\%) & 1.69 (123\%) & 1.05 (77\%) \\ L4–L5 & 0.92 & 0.81 & 1.27 \\ Total & 6.17 & 6.41 & 6.52 \\ \hline \multicolumn{4}{c}{**Stiffness (Nm/degree)**} \\ \hline L3–L4 & 3.28 (100\%) & 2.67 (81\%) & 4.85 (148\%) \\ \hline \multicolumn{4}{c}{**Disc max. stress (KPa)**} \\ \hline L2–L3 & 355 (100\%) & 357 (100\%) & 356 (100\%) \\ L3–L4 & 281 (100\%) & 505 (179\%) & 381 (135\%) \\ \hline \multicolumn{4}{c}{**Facet joint force (N)**} \\ \hline Left & Right & Left & Right & Left & Right \\ L2–L3 & 26 & 26 & 26 & 42 & 41 \\ L3–L4 & 36 & 36 & 35 & 15 & 14 \\ \hline \hline \end{tabular} Note: values in parentheses represent the normalized results ([DEF or NIPD]/INT] \(\times\) 100%).  
\end{table}
Table 3: Comparison of the biomechanical characteristics among the three FE models during extension.  
Figure 6: Stress distribution in the lumbar spine in the three FE models. Note: the circle indicates the location of the stress alteration. In the NIPD, the posterior element had higher stress (large area in red color), but the anterior vertebral body had lower stress (small area in yellow color).  
Figure 7: Disc stress distribution in the three FE models in extension: (**A**) implanted level L3–L4 and (**B**) adjacent level L2–L3. Note: the arrow indicates the region of high stress.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **INT** & **DEF** & **NIPD** \\  & **Moment: 12.9 Nm** & **Moment: 12.6 Nm** & **Moment: 12.6 Nm** \\ \hline \multicolumn{4}{c}{**ROM (degree)**} \\ \hline L1–L2 & 6.55 & 6.41 & 6.41 \\ L2–L3 & 5.89 (100\%) & 5.75 (98\%) & 5.76 (98\%) \\ L3–L4 & 5.51 (100\%) & 5.74 (104\%) & 5.70 (103\%) \\ L4–L5 & 5.16 & 5.19 & 5.20 \\ Total & 23.11 & 23.09 & 23.07 \\ \hline \multicolumn{4}{c}{**Stiffness (Nm/degree)**} \\ \hline L3–L4 & 2.34 (100\%) & 2.20 (94\%) & 2.21 (96\%) \\ \hline \multicolumn{4}{c}{**Disc max. stress (KPa)**} \\ \hline L2–L3 & 1110 (100\%) & 1080 (97\%) & 1090 (98\%) \\ L3–L4 & 1050 (100\%) & 1240 (118\%) & 1220 (116\%) \\ \hline \multicolumn{4}{c}{**Facet joint force (N)**} \\ \hline L2–L3 & Left & Right & Left & Right \\ L3–L4 & 29 & 20 & 24 & 17 & 24 & 16 \\ L3–L4 & 15 & 3 & 13 & 2 & 18 & 1 \\ \hline \hline \end{tabular} Note: values in parentheses indicate normalized results ([(DEF or NIPD)/INT] \(\times\) 100%).  
\end{table}
Table 4: Comparison of the biomechanical characteristics among the three FE models in lateral bending.