# Identification of Surgical Plan for Syndesmotic Fixation Procedure Based on Finite Element Method
## 4 Discussion  
A syndesmosis injury leads to damage and loss of ligaments constituting the complex structure of the ankle joint because of the various external shocks and loads transferred to the tibia inside the body. Such a complex injury requires thorough research to cover various cases. Therefore, many studies have employed the FE analysis [25; 26; 27; 28]. This study analyzed the effects of various parameters involved in screw fixation on the syndesmosis injury and determined an optimal location for screw fixation from a biomechanical perspective. To achieve these objectives, we set three parameters and derived the values of the maximum von Mises stresses and the syndesmosis widening. In the first step of the analysis, the screw level was evaluated. The trend in the values was similar, regardless of the remaining parameters. In other words, with the increase in the screw level from 10 to 25 mm, the stress and the syndesmosis widening were decreased, irrespective of the diameter and material of the screw and the number of penetrated cortical bones. The decrease in the stress indicates that, as the screw level increases, the stress acting on the screw is greater than that on the bone. In addition, even after checking the stress on the adjacent bone of the screw, the stress decreased as the level increased. The decrease in the syndesmosis widening indicates that the binding force between the bone and the screw is strong. Accordingly, if the screw is positioned at a level in the range of 20-25 mm, the stability of the syndesmosis increases. This result is supported by many other cadaveric biomechanical studies wherein similar values have been reported [6; 29]. The analysis in the second step was conducted in terms of the material of the syndesmotic screw, such as titanium and stainless steel. The stress acting on the stainless steel screws is lower than that acting on the titanium ones. However, when the elasto-plastic properties of the two materials were compared, the maximum stress of titanium did not exceed the yield stress, whereas that of stainless steel exceeded the yield stress [16; 20; 21; 30]. In addition, with respect to syndesmosis widening, the results of the widening show a firm basis for selecting a more appropriate material. Although the difference between the two materials did not occur in the stresses on the adjacent bone of the screw, the other results concluded that titanium is more stable than stainless steel. [PERSON] et al. conducted a cadaveric  
Figure 14: Analysis of the syndesmosis widening in terms of the number of penetrated cortical bones: (**a**) titanium screw with a diameter of 3.5 mm, (**b**) titanium screw with a diameter of 4.5 mm, (**c**) stainless steel screw with a diameter of 3.5 mm, and (**d**) stainless steel screw with a diameter of 4.5 mm. study and presented experimental results obtained by applying a force of 800 N to sixteen fresh frozen legs inserted with syndesmotic screws, which were fabricated from either stainless steel or titanium and had three or four cortical rolls. The results were found to be similar on the basis of the two parameters used, and it was specified that under no condition should a weight bearing load be applied [8]. However, unlike previous cadaveric studies, this study shows the relative advantages of the two materials. The internal stresses of the bones and screw were analyzed using an FE analysis. The results show that titanium exhibits a higher level of stability. In the third step of the analysis, we compared the von Mises stresses in terms of two different screw diameters: 3.5 and 4.5 mm. For most cases, the stress on the screw with a diameter of 4.5 mm is lower than that on the screw with a diameter of 3.5 mm. In addition, with regard to the syndesmosis widening, the preferable screw has a diameter of 4.5 mm. However, there was no difference between the two diameters in the stresses of the adjacent bone of the screw. Consequently, we may conclude that a screw with a diameter of 4.5 mm is more advantageous than that with a diameter of 3.5 mm.