Optimal suture-button orientation in dynamic fixation of injured syndesmosis " Finite Element Analiysis Study"

The aim of this study was to determine the ideal suture-button orientation, which would enable physiological ligamentous healing by limiting the rotational movement of the syndesmotic joint in axial plane and supraphysiological anterior- posterior translation in sagittal plane. A solid ankle model and a Sikka Stage 4 syndesmotic injury model were developed with finite element analysis. Fixation models which varies in number and orientation were designed to detect syndesmotic injury: traditional fixaiton type (Model 1), divergence fixation type (Model 2); imitation of AITFL and PITFL's anatomical axis fixation type (Model 3); vein, nerve, and tendon protective fixation type (Model 4); vein, nerve, and articular cartilage protective fixation type (Model 5). In order to simulate the Heel off phase, which is the 4th phase of the stance phase, 3528 N compressive force and 533 N tangential force with anterior orientation were applied to the tibial plateau at 10° dorsiflexion of the ankle. And displacement of fibula in anteroposterior & mediolateral planes, rotation angles in axial plane, A-TFCS and P-TFCS distances were evaluated. The results of the study indicated that the traditional fixation type did not provide sufficient dynamic stabilization in the syndesmotic injuries and the fixation method performed with double suture-button which was applied in the proper orientation and angle of PITFL and AITFL (Model 3) prevented the pathologic syndesmosis diastasis while enabling the anatomical reduction of syndesmosis and the physiological movement of the fibula. In addition, Model 5 which was designed to prevent neurovascular structures and articular cartilage damage during fixation, had 0,5343°deficiency in the prevention of pathological external rotation and had weakness in terms of restraining the supraphysiological displacement in the coronal and sagittal plane, %3 and %1 respectively, compared to Model 3. Also it was found that Model 5 provided almost ideal dynamic stabilization. In conclusion, instead of conventional suture-button application, model 5 fixation method, which provides multiplanar dynamic stability and minimizes the complication rate, is the fixation method that prevents the pathologic syndesmosis diastasis while enabling the anatomical reduction of syndesmosis and physiological movement of fibula. Key words: distal tibiofibular ligaments, syndesmotic injury, finite element analysis, dynamic fixation, suture-button orientation.