## 6 Discussion  
When designing and constructing external fixators, anatomical and biomechanical factors should be taken into account. From a biomechanical point of view, fracture fixation should have sufficient stability, which means a reduction in interfragmentary movement caused by external loads and muscle activity. In this paper, a comparative analysis of the biomechanical performance of the Sarafix external fixator was performed, which aimed to quantify the mechanical behavior of the fixator under the load from anterior-posterior bending for different frame materials, as well as different configurations of the fixator. Analyzing the results of displacement at the point of load from the perspective of the fixator configurations, we can notice that we have a slight difference in the values of displacement, i.e., both analyzed versions of the fixator B50 and C50 show almost equal values of displacement at the point of load. However, if we analyze the results of displacement at the load point from the perspective of the material of the fixator frame, then it can be seen that the fixator with a carbon frame has significantly higher displacements compared to the fixator with a steel frame, in the amount of up to 37% (for both configurations B50 and C50). Comparing the results of the transverse displacement of the ends of the bone segments at the fracture site from the perspective of fixator configurations, we can state that the B50 version has smaller displacement values than the C50 configuration in the case of the steel frame, in the amount of 5%, while in the case of the carbon frame, we have the opposite situation, i.e., the C50 configuration has smaller displacement values than the B50 configuration by the same amount as the steel frame case. Analyzing the results of the transverse movements of the ends of the bone segments at the fracture site from the perspective of the fixator frame material, we can notice that the fixator with a carbon frame has greater displacements at the fracture site compared to the fixator with a steel frame, in the amount of up to 45% (for configuration B50) or up to 31% (for configuration C50). The stiffness values of the designs of the fixator were determined based on the displacement of the point at the point of loading, while the stiffness values of the fracture were determined based on the relative displacement of the analyzed pair of points of the bone segments at the fracture site (Figure 4). In the absence of major rotations, deformations, sliding joints, and plastic deformation of the fixator frame components, which is the basic requirement in terms of preserving the anatomical reduction in bone fragments in postoperative load conditions, the conducted research showed that there is a linear dependence between the load and the displacement of the bone segments, identically to the case of loading of the fixator to axial pressure [19]. Based on the anterior-posterior bending tests, we can note that both analyzed versions of the fixator B50 and C50 (for both frame materials) show almost equal values of structural  
Figure 12: Displacement at the site of fracture for configuration C50; (**a**) F = 0 N, (**b**) F = 500 N.  
stiffness and ensure similar fracture stiffness. This means that the influence of placing two half-pins in a plane at 45\({}^{\circ}\) to the AP plane and their distance from the load point did not significantly affect the reduction in the values of the analyzed stiffnesses according to AP bending. Also, the difference in stiffness between the B50 and C50 versions is expressed to a lesser extent than in the case of the fixator loading on axial pressure [19]. Analyzing the stiffness results from the perspective of the fixator frame material, we notice that the stiffness of the structure for both test configurations of the fixator is lower in the fixator with a carbon frame compared to the fixator with a steel frame by up to 27%.