## 3 Results  
### Validation of CAD-Based Patient-Specific Nuss Bar Design Technology  
To fabricate the patient-specific Nuss bar, we reviewed the CT images of 15 patients and chose one symmetric case called Patient No. 1 from the symmetric group. Then, we proposed three surgery scenarios (Nuss bar insertion points) to derive the patient-specific Nuss bar shape and select the insertion point for Patient No. 1. The HI value before and after inserting the Nuss bar was calculated for each scenario. The pre- and post-operative maximum transverse diameters (A, A\({}^{\prime}\)) and the minimum AP distances (B, C), and HI values are summarized in Table 5.  
According to a previous study, the post-operative maximum transverse diameter is 95% of the pre-operative value [17]. The post-operative maximum transverse diameter (A\({}^{\prime}\)) was derived by applying the results of the corresponding study. \begin{table}
\begin{tabular}{c c c} \hline
**Index** & **Description** & **Value** \\ \hline
0 & Inner bending roller diameter (mm) & 19.050 \\
1 & Outer bending roller diameter (mm) & 19.050 \\
3 & Upper Roller Center to X (mm) & 27.305 \\
10 & Tool type (\#) & 5 (=Mandrel cluster) \\
11 & Tool Cluster Diameter & 75.001 \\ \hline \end{tabular} Notes: Setting values for all items except for index numbers 0, 1, 3, 10, 11 on the Tool Geometry window are “0”.  
\end{table} 
Table 4: Tool geometry setting values for increasing accuracy of bending result. \begin{table}
\begin{tabular}{c c c} \hline
**Index** & **Description** & **Value** \\ \hline
0 & Default Units & 0.0000 \\
1 & Stop Machine if done & 0.0000 \\
6 & Return Bender Speed & 100.0000 \\
7 & Delay at the end of program & 0.0000 \\
12 & Cut at the end of program & 3.0000 \\
16 & Negative \(Z\)-axis limit & \(-\)200.0000 \\
17 & Positive \(Z\)-axis limit & 200.0000 \\
18 & Initial Feeder position * & 756.750 \\
19 & Initial Bender position & 0.0000 \\
20 & Output ON Delay & 80.0000 \\
21 & Output OFF Delay & 80.0000 \\
23 & Feeder Clamp move to grip & 0.0000 \\
24 & Arm Collision detection Rotation Default & 5.0000 \\ \hline \end{tabular}  
* Initial feeder position is defended on length of material (Nuss bar length)  
\end{table} 
Table 3: Operating parameter values to operate the CNC bending machine for the Nuss bar. Figure 10 shows the pre- and post-operative minimum AP distances according to the Nuss bar insertion point. The B (Pre-operative) values for each insertion point (points A, B, and C) were measured at 73.01 mm, 68.61 mm, and 73.30 mm, respectively. The smallest value was obtained at position B. The C values for each insertion point were 101.11 mm, 103.49 mm, and 104.15 mm, respectively. The largest value was obtained at position C. The minimum AP distance increased by 38.49%, 50.84%, and 42.09% at the insertion points, respectively. Thus, position B showed the largest increase. Figure 11 shows the changes in HI values before and after the Nuss procedure. Figure 11: Haller index before and after the Nuss procedure. The values of the Haller index with insertion points of the Nuss bar are shown in the histogram. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Point**} & **A (mm):** & **A’ (mm):** & **B (mm):** & **C (mm):** & **HI:** & **ICI:** \\  & **Pre-Op.** & **Post-Op.** & **Pre-Op.** & **Post-Op.** & **Pre-Op.** & **Post-Op.** \\ \hline A & 217.86 & 206.97 & 73.01 & 101.11 & 2.98 & 2.05 \\ B & 215.22 & 204.46 & 68.61 & 103.49 & 3.14 & 1.98 \\ C & 217.57 & 206.70 & 73.30 & 104.15 & 2.97 & 1.98 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Haller index values before and after the Nuss procedure in Patient No. 1. Figure 10: Minimum AP distance before and after the Nuss procedure. Values of minimum AP distance with Nuss bar insertion points are shown by histogram. The post-operative HI value decreased by 31.31% from 2.98 to 2.01 at insertion point A, by 36.94% from 3.14 to 1.98 at insertion point B, and by 33.33% from 2.97 to 1.98 at insertion point C. At every insertion point, the HI value improved by more than 30%.