INFLUENCE OF ANKLE POSITION AND CORTICAL PURCHASE ON SYNDESMOTIC SCREW FIXATION IN SIMULATED WEBER C ANKLE INJURIES.

Background: Syndesmotic injuries associated with Weber C ankle fractures remain a significant challenge in orthopaedic practice because inadequate reduction may adversely affect ankle stability and long-term functional outcomes. Although syndesmotic screw fixation is widely performed, controversies persist regarding the optimal ankle position during screw insertion and the ideal degree of cortical purchase required for stable fixation.Aim: To evaluate the biomechanical effects of ankle position during syndesmotic screw insertion and cortical purchase depth on syndesmotic width, tibiotalar rotation, ankle dorsiflexion, and construct stability in a cadaveric Weber C ankle injury model.Methods: This cadaveric biomechanical study was conducted using fresh-frozen human lower limb specimens with a simulated Weber C syndesmotic injury. Syndesmotic fixation was performed using 3.5-mm cortical screws inserted with the ankle maintained either in dorsiflexion or plantarflexion and using tricortical or quadricortical purchase. Biomechanical testing was carried out under axial loading and combined rotational loading conditions. Syndesmotic width, tibiotalar rotation, maximal ankle dorsiflexion, and construct failure characteristics were assessed and compared between groups.Results: Plantarflexion fixation demonstrated relative syndesmotic narrowing under all loading conditions, whereas dorsiflexion fixation resulted in relative widening, with significant differences observed between groups (p < 0.05). Tibiotalar rotation was significantly greater in the dorsiflexion group under isolated axial loading but became comparable under higher rotational torque. No statistically significant differences were identified in maximal ankle dorsiflexion between plantarflexion and dorsiflexion groups for either tricortical or quadricortical fixation. Similarly, construct failure torque and failure angle did not differ significantly between fixation positions.Conclusion: Ankle position during syndesmotic screw insertion significantly influences syndesmotic width behaviour under loading conditions, with plantarflexion tending towards relative over-compression and dorsiflexion towards relative widening. However, neither ankle position nor cortical purchase depth significantly affected ankle dorsiflexion or construct failure characteristics. Accurate syndesmotic reduction and careful intraoperative assessment remain essential irrespective of fixation strategy.