## 3 Results and Discussion
### Numerical Assessment of Broken Fibula Deflections, Which Is Fixed with an Extracortical Plate  
The object of numerical analysis is the deformed state of the \"fibula-extracortical titanium plate\" composition under the action of the fixing tightrope tightening force (Figure 2c), taking into account the damage to the fibula tissues (rupture). Having analyzed Equations (13)-(15) and (19), we determined a graphical dependence of the damaged bone deflections on the value of the fixing tightrope tightening force (Figure 7). By gradually increasing the value of the tightrope tightening force, we control that the maximum bone deflection does not exceed the permissible value [\(w\)]. The value of the tightrope tightening force \(P\), under which the condition \(w(x)=w_{\text{max}}=[w]\) is satisfied, will correspond to the permissible value of the tightrope tightening force [\(P\)] = \(P\). The permissible deflection value is selected from the condition of preserving the geometrically correct shape of the bone after rupture consolidation (healing) [69; 70; 71]. If the permissible deflection value is exceeded, a crack or the edges of a broken bone may open, as well as damage to the crack edges when they come into contact, displacement of bone fragments, etc. Therefore, the criterion for selecting the permissible value of the tightrope tightening force is the boundary value of the bone deflection, at which the stiffness condition is still satisfied. Using the result of solving the problem of determining the broken bone deflections in (13)-(15), (19) and equating the maximum deflection \(w_{\text{max}}\) to the permissible deflection value [\(w\)], the following is finally obtained  
Figure 5: Distribution of maximum stresses along the fibula length from the action of the tightrope tightening force: 1—the tightening force for a tall person is \(P\) = 160 N; 2—the tightening force for a small person is \(P\) = 75 N.  
Figure 6: Distribution of displacements along an intact fibula: (**a**) rotation angles of cross-sections; (**b**) bone deflections; 1—the tightrope tightening force for a tall person is \(P\) = 160 N; 2—the tightrope tightening force for a small person is \(P\) = 75 N.  
(21)  
The influence of the fixing plate geometrical parameters on the permissible value of the tightrope tightening force is of great interest (Figure 8). It can be seen that an increase in the length, thickness, and angular measure of the plate cross-section arc leads to an increase in [\(P\)]. Analysis of the graphical dependences presented in Figure 8 makes it possible to observe the change in the gradient of such growth. Analytical assessments of the influence of the plate physical-geometrical parameters on the permissible value of the tightrope tightening force can be performed using Equation (21). The vast majority of innovations proposed for implementation in the field of traumatology and orthopedics are successfully realized into practice due to a multidisciplinary approach to solving problems. Figure 8: Dependence of the permissible value of the tightrope tightening force [\(P\)] on fixing plate geometrical parameters: (**a**) dependence [\(P\)] on the plate length \(l_{p}\); (**b**) dependence [\(P\)] on the plate thickness \(\delta\); (**c**) dependence [\(P\)] on the angular measure of the plate cross-section arc \(2\alpha\). Figure 7: Deflections of the broken fibula, fixed with an extracortical plate: (**a**) the permissible value of tightrope tightening force for a tall person is [\(P\)] = 66 N; (**b**) the permissible value of tightrope tightening force for a small person is [\(P\)] = 28 N.  
In the papers [69; 70; 71; 72], the fixation of a broken shin bone using an extracortical plates of various configurations has been studied, and the distribution of mechanical stresses in the bone and plate has been determined. In work [73], the fatigue strength of steel and titanium extracortical plates for a fibula was found.