# Identification of Surgical Plan for Syndesmotic Fixation Procedure Based on Finite Element Method
## 4 Discussion
[PERSON] and [PERSON] evaluated the stability of twelve cadaveric leg specimens inserted with stainless steel syndesmotic screws with diameters of 3.5 and 4.5 mm. The sub-maximal axial ramp (0 to 1200 N) test and the axial fatigue test (0 to 900 N) were conducted on the specimens. They concluded that the screws with diameters of 3.5 and 4.5 mm did not exhibit any biomechanical difference in syndesmotic fixation [31]. In contrast, the simulation results of this study show that a screw with a diameter of 4.5 mm is more advantageous. Accordingly, this study supplements the cadaveric studies. However, in another cadaveric study, [PERSON] et al. applied four cortical techniques to eighteen specimens for inserting screws with diameters of 3.5 and 4.5 mm and measured the shear stresses. Because the yield and peak loads of the screw with the diameter of 4.5 mm were higher than those of the screws with the diameter of 3.5 mm, they concluded that the larger the screw diameter, the greater is the resistance of the screw to shear stresses [32]. Hence, we believe the screw diameter should be selected on the basis of a comprehensive examination including the FE analysis of the shear stress. In the fourth step of the analysis, we examined the biomechanical effect of the number of penetrated cortical bones on syndesmosis fixation. With regard to the two cases wherein three and four cortical bones were penetrated, the stress was no different in all cases. With respect to the values of syndesmosis widening, these were lower in the case wherein four cortical bones were penetrated compared with those in the case wherein three cortical bones were penetrated for a diameter of 3.5 mm. However, there was no difference for a diameter of 4.5 mm. The widening in the case wherein four cortical bones were penetrated was lower, but as the diameter increased, its influence decreased. On the other hand, the stresses at the adjacent bone of the penetrating four cortical bones decrease as the level increases. In another cadaveric study, [PERSON] et al. concluded that the number of penetrated cortical bones made no biomechanical difference. [PERSON] et al. checked the conditions of patients for 150 days after syndesmotic fixation. The screw failure was 8% among patients who secured stability through three cortical fixations, whereas the screw failure in patients treated with four cortical fixations was 7%. Based on this data, it was speculated that both three and four cortical fixation techniques were useful for ensuring stability of the syndesmosis. Moreover, they showed that the stability in the case of three cortical fixations tended to decrease when no weight restriction was imposed [33]. This can be verified using the FE analysis results of this study, wherein it is demonstrated that the stability in the case of three and four cortical fixations are high. Many parameters can be employed in a cadaveric or FE analysis to identify the biomechanical characteristics of the syndesmotic screw fixation. In addition to the parameters employed in this study, such as the level, material, and diameter of the screw and the number of cortical bone penetrations, many other parameters exist including the density of cancellous bone according to age and sex of patients, the number of fixed screws, load conditions (compressive and rotation forces), phases of human walking, and surgical conditions. In particular, the external rotational motion of the ankle joint is a major factor in ligament injury. Accordingly, it will be the subject of future study. The finite element analysis was carried out by substituting the change according to the number of screws in this study among these limit conditions. Another screw was added based on the parameters at the 4.5 mm diameter and 25 mm level of the titanium screw with four cortical bones, from the results of this study. This involves inserting two screws by adding one screw of another level to a 25 mm level screw.