## 3 Results  
### Extension  
Maximum stress values at the center of the vertebral body and intervertebral disc from T10 to L2 vertebrae are shown in extension (Table 3 and Figure 5). Comparisons between the healthy model and DISH flat model showed that stresses were greater on the vertebral body and intervertebral disc from T10 to L2 in extension (Figure 6) than in the healthy model. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & **Depth of** & **Depth of** & **Depth of** & **Depth of** \\  & & & & **Discontinuity** & **Discontinuity** & **Discontinuity** \\  & & & & **5.0 mm** & **10.0 mm** & 5.0 mm & **10.0 mm** \\
**Healthy** & **DISH Flat** & **Thickness** & **Thickness** & **The Radius of** & **The Radius of** & **The Radius of** & **The Radius of** \\
**5 mm** & **DISH Flat** & **5 mm** & **10 mm** & **Curvature of** & **Curvature of** & **Curvature of** & **Curvature of** \\
**5 mm** & **(T-5)** & **(T-10)** & **(T-10)** & **the Central** & **the Central** & **the Central** & **the Central** \\
**5 mm** & & & & **Groove** & **Groove** & **Groove** \\
**5 mm** & & & & **2.5 mm** & **1.0 mm** & **1.0 mm** \\
**5 mm** & & & & **(D-5/R-2.5)** & **(D-10/R-2.5)** & **(D-5/R-1)** & **(D-5/R-1)** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Elements of the nodes of each model are shown. Figure 5: The highest value for maximum von Mises stress on the vertebral body and intervertebral disc (MPa) in extension. The vertical axis is stress (MPa), and the horizontal axis is each vertebral body and intervertebral level. In the T-5 model and T-10 model, the stress on the vertebral body was similar with greater ossification in extension (Figure 7). As the thickness of ossification increased, stress on the intervertebral disc decreased. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Extension**} \\ \hline  & **Healthy** & **DISH Flat** & **T-5** & **T-10** & **D-5/R-2.5** & **D-10/R-2.5** & **D-5/R-1** & **D-10/R-1** \\ \hline T10 & 1.17 & 7.99 & 8.25 & 8.4 & 7.79 & 8.35 & 7.93 & 8.11 \\ T10/11 & 1.22 & 17.03 & 17.04 & 17.32 & 17.49 & 16.38 & 17.61 & 17.53 \\ T11 & 4.27 & 12.05 & 11.94 & 13.37 & 11.23 & 10.81 & 10.85 & 11.26 \\ T11/12 & 1.7 & 26.94 & 7.88 & 2.85 & 3.64 & 3.08 & 3.26 & 2.92 \\ T12 & 6.37 & 16.64 & 16.67 & 16.81 & 52.89 & 61.04 & 58.2 & 57.62 \\ T12/L1 & 2.27 & 37.55 & 39.11 & 39.43 & 3.69 & 2.44 & 3.53 & 2.12 \\ L1 & 8.2 & 24.36 & 23.88 & 23.49 & 24.79 & 24.81 & 24.7 & 24.89 \\ L1/2 & 2.38 & 42.33 & 39.81 & 40.03 & 43.02 & 42.33 & 41.36 & 43.36 \\ L2 & 3.47 & 25.47 & 27.42 & 26.87 & 25.15 & 26.45 & 26.19 & 25.44 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The highest value for maximum von Mises stress on the vertebral body and intervertebral disc (MPa). Figure 6: Only vertebral bodies and discs are shown for clarity. The right bar is color-coded according to stress (MPa). Stress diagrams of (**a**) the healthy model and (**b**) the diffuse idiopathic skeletal hyperostosis (DISH) flat model. Stresses were greater in the flat model in extension than in the healthy model. Figure 7: In extension analyses of the hypertrophic ossification models T-5 (**a**) and T-10 (**b**), the stress on the intervertebral disc at T11–T12 was reduced, whereas stress on the vertebral body was unchanged. Figure 11: Only vertebral bodies and discs are shown for clarity. The right bar is color-coded according to stress (MPa). Stress diagrams of (**a**) the healthy model and (**b**) the DISH flat model. Stresses were greater in the flat model in flexion than in the healthy model.