# Methodology of Multicriterial Optimization of Geometric Features of an Orthopedic Implant
## 3 Results
### Strength Verification  
Strength has been verified by checking whether a specific implant will not be damaged during its implantation and normal functioning of the patient after the reconstruction of the anterior cruciate ligament.  
Verification of the implantation process  
One of the most critical moments during the surgery is the moment when the graft is installed through the bone tunnel in the tibia and femur. An additional advantage of using implants is the protection of the graft during its implantation. In order to be able to estimate the value of the force required to install the graft, Prof. [PERSON] developed a special device for measuring force, using a linear force meter of the FB series with a digital analyzer by AXIS [23]. The maximum force that was recorded was 400 N, and this was also the force used in the strength analysis of the implant.  
During the simulation (in the ANSYS Workbench program), the force was applied (Figure 18) to the inner walls of the implant tunnel, towards the exit from the tunnel (oriented facing upwards, along the axis of the implant, which is the red area), while the implant has been fixed on its outer surface and on one of the walls of the tunnel exit (blue area). To avoid the maximum stresses accumulated at the edges of the surface, all edges were rounded.  
The simulation results are presented in the following figures:  
* Figure 19--stress results. A maximum stress of 1.66 MPa has been observed at the edge of one of the holes on the implant surface;
* Figure 20--results of implant deformation. The maximum deformation (equal to 8.8 \(\times\)10 \({}^{-4}\) nm) can also be observed at the edge of one of the holes at the bottom of the implant, oriented to the knee direction.  
The conducted tests showed the weakest areas of the implant. They turned out to be areas around the holes on the implant surface. Despite these areas, the test implant should withstand the process of dragging the graft through it while it is anchored in the bone.  
Verification of the strength of the implant in the bone  
The implant obtained during optimization using the objective function was inserted into the bone model at the appropriate angle (this angle was measured on DICOM images (from MRI) of patients after anterior cruciate ligament reconstruction).  
The _Pauwelsa_[24] model has been used to determine the load on the femur (the calculations have been based on the model of a two-arm lever realizing the loads on the femoral head while standing on one leg).  
The calculated forces have been plotted on a bone model (Figure 21). A force R (211,043 N) was applied at an angle of 25\({}^{\circ}\) to the head of the cortical bone. A force F (155,524 N) was applied at an angle of 35\({}^{\circ}\) to the epiphysis of the femoral head.  
Figure 18: Applied force and implant fixation.  
Figure 19: Stress distribution in the implant.  
Figure 20: Distribution of deformation in the implant.  
The results of the strength simulation showed that most of the load is transferred by hard tissue, therefore the loads transmitted to the soft tissue and the implant have not been significant.  
Selected simulation results have been presented in the figures below:  
Figure 22--stresses in the cortical bone tissue;  
Figure 23--stresses in the spongy tissue and in the implant.  
Figure 21: Define a restraint site and apply forces to the femur.  
By analyzing the obtained results, it has been found that the implant would not be damaged at the first phase of the patient's convalescence during the permitted activities.  
Both the stages of the strength simulation confirmed that the implant will not be damaged.