# \"In Vivo\" Validation of 3D-Printed Innovative Surgical Template for Lumbar Spinal Arthrodesign.
## 4 Results  
Quantitative comparative analysis with freehand surgery and custom-made template-assisted surgery are synthetically shown in the following tables. Data reported in the tables are mean values among the surgeries. The detailed information about each case treated is reported in Online Resource 2. The comparative analysis of the values in Table 1 shows an improvement of the analysed parameters that is not dependent on the verteb on which the surgery is done. The improvement is highlighted both in the mean values and in variance. The independence of the results towards the operated-upon verteb is a strong point of the procedure. The mean value of X-ray shots, that is, as shown in the table, about equal to 3, is perfectly matching what is required in the procedure: one X-ray shot for template positioning before the verteb drilling, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Number of** & **X-Ray** & **Time** & **Kirshner** & **Screws** \\  & **Samples** & **Shots** & **(min)** & **Repositioning** & **Repositioning** \\ \hline \multicolumn{6}{c}{**Freehand**} \\ \hline
1.1 & 2 & 10.0 & 57.5 & 3.5 & 0.0 \\
1.2 & 4 & 9.0 & 66.8 & 5.5 & 0.3 \\
1.3 & 10 & 22.4 & 60.6 & 5.5 & 0.4 \\
1.4 & 5 & 17.0 & 47.4 & 5.8 & 0.0 \\
1.5 & 8 & 12.4 & 69.6 & 6.6 & 0.1 \\ \hline \multicolumn{6}{c}{_Total_} & _Mean_ & 15.8 & 60.9 & 5.7 & 0.2 \\
**30** & _St. Dev._ & 16.1 & 30.7 & 3.8 & 0.5 \\ \hline \multicolumn{6}{c}{**Guided hand**} \\ \hline
1.1 & 5 & 2.6 & 12.6 & 0.4 & 0.0 \\
1.2 & 5 & 2.6 & 12.8 & 0.4 & 0.0 \\
1.3 & 4 & 2.3 & 13.8 & 0.5 & 0.0 \\
1.4 & 12 & 3.1 & 15.5 & 0.3 & 0.0 \\
1.5 & 3 & 3.7 & 16.7 & 1.3 & 0.0 \\ \hline \multicolumn{6}{c}{_Total_} & _Mean_ & 2.8 & 14.3 & 0.5 & 0.0 \\
**30** & _St. Dev._ & 0.9 & 3.9 & 0.7 & 0.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Quantitative parameter results. one X-ray shot for verification of the trajectories during the screw implanting, and the final X-ray shot for verifying the final screw positioning. Rarely were the Kirschner wires repositioned during the surgery, while the screws were never repositioned (nor for freehand and for guided insertion, probably thanks to the high number of X-ray shots in the freehand cases and to the use of template in the guided cases). Table 2 shows the comparison of the qualitative data acquired during the surgeries. The surgeon, just after the surgery, was asked to express a motivated judgement on a 5-point scale (1 = very poor, 5 = very good) about the qualitative parameters, just analysing the post-operative X-ray or CT. The comparison shows a mean value of improvement of the judgements equal to 10%. The reference value is the best judgement the surgeon expressed on the manual insertion. To check the significance of results of qualitative comparison, a Wilcoxon signed-rank test was performed on the qualitative data: pedicle centring, alignment, and screw convergence. The Wilcoxon test is appropriate because it is a nonparametric test designed to evaluate the difference between two treatments or conditions when the samples are correlated. The data considered for the two test cases were the case \"with template\" and the case \"without template\". Table 3 shows the comparison results for two non-null hypotheses: \(p\)-value \(<\) 0.01 and \(p\)-value \(<\) 0.05. No significant differences were found among those data except for the case of screw convergence that was checked as significantly better (\(p\)-value \(<\) 0.05) in the case \"with template\". Table 4 synthetises the percentage of improvement of each acquired data point (quantitative and qualitative) without considering the type and level of the verteb. Figure 5 also synthetically shows how the use of the surgical template allows improvement of every analysed parameter.