## 3 Results and Discussions
### Results for Scenario with Callus Formation  
The scenarios taking into account the impact of callus formation are presented next. The first four weeks after EF placement are considered, as full weight-bearing should be feasible during this period based on the clinical practice. The following situations were analyzed: (1) metallic EF without wire pre-tension; (2) metallic EF with 500 N of wire pre-tension; and (3) 3D-printed PLA-CF ring without wire pre-tension. It should be mentioned that, for the PLA-CF ring, as shown in gap configuration analyses, for the current design, it was not possible to apply 500 N of wire pre-tension or more as the calculation convergence criteria were not satisfied within a reasonable number of iterations (<100). The pin reaction force was used to quantify the load transferred by the EF for each healing phase. Table 4 shows the pin reaction force (Fr) evolution for the case with a 0.1 g sit position in conjunction with the percentage of the total axial applied load of 70 N (P%). The following aspects can be observed:  
* Pin reactions decrease with the healing of the fracture as the bone is taking a higher load and the EF is less effective;
* Pin reactions are similar for metallic and PLA-CF EF configurations;
* Adding the pre-stress for metallic EF was found to significantly increase the pin reactions. Figure 13 presents the displacements in the axial Z direction and in the transverse Y direction for different callus ages (i.e., stiffness). As observed, the displacements are within acceptable limits (less than 30% in the axial direction and 15% in the transverse direction), except for the fibrous callus under 1 g axial loading corresponding to the one-leg stance condition necessary to walk. The results showed that, due to high displacements at the fracture site, if healing proceeds normally, full weight bearing should be possible at the earliest after 2 weeks post-surgery. The stress values for the steel EF without pre-tension configuration are presented in Table 5, while Table 6 shows the stress values for the 3D-printed PLA-CF EF without pre-tension. For the granulation tissue callus stage, only the 0.1 g loading case was analyzed, as the patient remains in bed rest during the first postoperative day. The stress values obtained for the metallic EF configuration are within acceptable limits for all components. As callus healing progresses, stress values decrease significantly, indicating improved load distribution and enhanced structural stability of the fixator-bone configuration. The stress values obtained for the PLA-CF EF configuration are similar with those of the metallic EF configuration (Table 7). The wires and the ring stresses are, on average, about 12%, and 70% lower for the PLA-CF EF configuration, while the callus stress is up to 4% higher. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Case 0.1 g**} & \multicolumn{4}{c}{**Reaction Force Resultant Pin Contact (Percentage of Total Axial Load of 70 N)**} \\ \hline \multirow{3}{*}{Callus healing stage} & \multicolumn{3}{c}{Metallic EF} & \multicolumn{2}{c}{Metallic EF} & \multicolumn{2}{c}{PLA-CF EF} \\  & \multicolumn{2}{c}{Case without} & \multicolumn{2}{c}{Case with 500 N} & \multicolumn{2}{c}{Case without} \\  & \multicolumn{2}{c}{pre-tension} & \multicolumn{2}{c}{pre-tension} & \multicolumn{2}{c}{pre-tension} \\  & \multicolumn{2}{c}{F\({}_{\text{r}}\) [N]} & P\% [\%] & F\({}_{\text{r}}\) [N] & P\% [\%] & F\({}_{\text{r}}\) [N] & P\% [\%] \\ \cline{1-1} Granulation tissue & 0 & 29 & 42 & 64 & 91 & 31 & 44 \\ \cline{1-1} Fibrous & 0.4 & 25 & 36 & 47 & 67 & 26 & 37 \\ \cline{1-1} Fibrous–Cartilage 2 w & 2 & 21 & 30 & 37 & 53 & 21 & 30 \\ \cline{1-1} Fibrous–Cartilage 4 w & 4 & 19 & 28 & 30 & 43 & 19 & 28 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Reaction force resultant at bone-to-pin contact. Figure 13: Displacements in Z and Y directions for the three analyzed situations: (**a**) Z direction, and (**b**) Y direction.