## 3 Results and Discussion
### OWHTO Geometric Planning Optimization  
The osteotomy wedge during the OWHTO should be carried out after careful geometric planning because its size and positioning depends on the purpose of the intervention with  
Figure 10: Transfer of the load medial–lateral tibial plateau. the achievement of the proposed goal: to eliminate the axial deviation of the mechanical axis of the foot affected by OA. The four established variables (V1, V2, V3, V4), (Figure 6a,b) characterize geometrically the osteotomy wedge completely. The results of the numerical analyses of equivalent stress, shear stress and displacement were recorded for each combination of levels of variation in the variables, taking into account the experimental design obtained by the Taguchi method. These are presented in Table 3. Obviously, the optimal criterion followed is that in which the values of the parameters of the three response functions (equivalent stress, shear stress and displacement) are minimal. A first observation is that for all three response functions, the values domain of the results obtained is quite large. Thus, the maximum values in relation to the minimum are approximately twice as high, and this demonstrates the fact that an improper choice of the values of V1, V2, V3, V4 can cause a doubling of the stresses and deformations in the CORA area of the tibia subjected to angular correction. From the analysis of the results presented in Table 3, the importance of the geometric positioning of CORA was noticed, especially with respect to the lateral cortex of the tibia (V2). In all cases where V2 has a minimum value of 7.5 mm, there are very high values of equivalent stress but also of the other two response functions. It follows that lower values for this variable (5 mm), recommended in some research [35; 36; 37], will produce equivalent and higher voltages, which can lead to microcracks in the CORA area. Even for a V2 equal to 7.5 mm, it can be seen that, in the case of the combination of parameters from code 6, a value of the equivalent stress is obtained very close to the ultimate compression tensile value for the human tibia, which is around 200 MPa [40]. Combination 6 is the most unfavorable in terms of stress and strain states in CORA for angular corrections higher than 12\({}^{\circ}\), and combination 5 for small correction angles of 6\({}^{\circ}\). At the opposite pole are the combinations of codes 4 (12\({}^{\circ}\) correction angle) and 7 (6\({}^{\circ}\) correction angle), for which all three response functions have the lowest values. Figures 11 and 12 show the distributions of the equivalent stress, shear stress and displacement for codes 6 and 7. It is also worth noting that, although some research [28; 38] optimizes these parameters, the combinations between them are often limited. The results obtained in the research demonstrate the need and importance of optimizing all geometric parameters and completing some previous results, which took into account, for example, only two parameters, V1 and V4 [28]. In order to be able to observe the influence that the four stress and displacement variables have, a statistical processing of the obtained results was also performed. Thus, a regression analysis was initially performed and the regression equations presented in Table 4 were obtained. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Code** & **V1** & **V2** & **V3** & **V4** & **Equivalent Stress** & **Shear Stress** & **Displacement** \\ \hline
1 & 30 & 7.5 & 15 & 6 & 168.65 & 90.77 & 1.18 \\ \hline
2 & 30 & 7.5 & 15 & 12 & 170.62 & 90.33 & 1.14 \\ \hline
3 & 30 & 10 & 20 & 6 & 99.6 & 53.23 & 0.6 \\ \hline
4 & 30 & 10 & 20 & 12 & 97.13 & 51.28 & 0.58 \\ \hline
5 & 40 & 7.5 & 20 & 6 & 185.25 & 97.91 & 1.34 \\ \hline
6 & 40 & 7.5 & 20 & 12 & 199.29 & 104.84 & 1.48 \\ \hline
7 & 40 & 10 & 15 & 6 & 99.91 & 52.09 & 0.58 \\ \hline
8 & 40 & 10 & 15 & 12 & 105.2 & 55.07 & 0.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameter values (equivalent stress, shear stress, displacement) obtained by applying FEM.