Hybrid Fixation Restores Tibiofibular Kinematics for Early Weightbearing after Syndesmotic Injury

Abstract

Category: Ankle Introduction/Purpose: Injury to the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), and interosseous membrane (IOM) of the syndesmosis is a predictive measure of residual symptoms after an ankle injury. Unstable syndesmotic injuries are typically treated surgically with constructs consisting of cortical screw and/or suture button fixation. Previous studies have shown contradicting findings regarding the effects of different surgical fixation methods on tibiofibular kinematics. Thus, the objective of this study was to quantify tibiofibular joint motion with different syndesmotic screw and suture button fixation constructs after disruption of the syndesmosis compared to the intact ankle during simulated weight bearing. Methods: Five fresh-frozen human cadaveric specimens were tested using a six degree-of-freedom robotic testing system. After subtalar joint fusion, the tibia and calcaneus were rigidly fixed to a robotic manipulator, while complete fibular length was maintained and fibular motion was unconstrained. A constant 200 N compressive load was applied to the ankle while an additional 5 Nm external rotation and 5 Nm inversion moment applied independently to the ankle at 0°, 15°, and 30° plantarflexion and 10° dorsiflexion. Fibular motion with respect to the tibia was tracked using an optical tracking system. Outcome variables included fibular medial-lateral (ML) translation, anterior-posterior (AP) translation, and external rotation (ER) in the following states: intact ankle, complete injury (AITFL, PITFL, and IOM transected), single tricortical screw fixation double tricortical screw fixation, hybrid fixation (single tricortical screw and single suture button), suture button fixation, and divergent suture button fixation. Repeated measures ANOVA was performed for statistical analysis. Results: The external rotation moment produced significant differences in fibular motion between the injury and fixation states compared to the intact state. A complete syndesmotic injury caused significantly increased fibular lateral translation, posterior translation, and external rotation in all ankle positions except 30° plantarflexion compared to the intact ankle. Single suture button and single screw fixation resulted in significantly higher fibular lateral translation at 10° dorsiflexion compared the intact ankle, while single suture button fixation also resulted in significantly higher external rotation at 10° dorsiflexion compared the intact ankle. Fibular posterior translation was significantly higher with hybrid, suture button, and divergent suture button fixation at 0° flexion and with single tricortical screw and double screw fixation at 10° dorsiflexion compared to the intact ankle (Figure 1). Conclusion: Complete injury to the syndesmosis results in significantly higher fibular lateral translation, external rotation, and posterior translation compared to the intact ankle. Hybrid or divergent suture button fixation would be recommended to restore tibiofibular motion without over-constraint. However, none of the fixation methods were able to restore AP translation in all ankle positions. Thus, it is important to evaluate syndesmotic stability in the sagittal plane at different ankle positions. Findings of this study suggest that physicians should evaluate fibular AP translation in a neutral position when using suture button fixation constructs and in dorsiflexion when using tricortical screw fixation constructs.