Effect of Plate and Screw Fixation on Stability of Weber B/Supination-External Rotation Fractures with Partial Deltoid Ligament Injury (SER4a): Robotic-Based Joint Testing

Category: Trauma; Ankle Introduction/Purpose: Fibular fractures with signs of concomitant deltoid ligament injury have been operated on with plate and screw fixation of the fibula for decades. More recently, clinical studies have suggested that some fibular fractures have only partial deltoid ligament injury and that the deep posterior tibiotalar ligament may be intact (SER4a), allowing for nonoperative treatment. The purpose was to determine whether fibula fracture fixation using plate and screws improves stability and restores normal joint kinematics in such fractures. It was hypothesised that fixation of the fibula fracture does not add significantly to the stability of SER4a models or restore normal joint kinematics. Methods: Fifteen cadaveric foot and ankle specimens underwent biomechanical testing using a six-degrees-of-freedom force- movement robotic arm in three states: intact joint, SER4a model (anterior inferior tibiofibular ligament sectioned + oblique trans syndesmotic fibular osteotomy + superficial layer of deltoid ligament sectioned + deep anterior tibiotalar ligament sectioned) and SER4a model + plate and screw fixation of the fibula. Joint stability was measured in lateral translation, valgus, and talar internal- and external rotation in three talocrural joint positions: 20° plantarflexion, neutral, and 10° dorsiflexion. Fluoroscopy was used to measure isolated talar lateralisation and talar tilt. The foot was rigidly fixed to a custom pedestal, while the tibia was rigidly fixed to the robot arm through a load cell. Talar lateral translation at neutral ankle position was the primary outcome. Results: Fixation of the fibular fracture reduced lateral translation by 0.16 millimetres (P = .101) at neutral ankle position (See Figure 1). In general, the tests for lateral translation and valgus showed no differences between the SER4a models and the SER4a models with fibular fracture fixation. As for talar internal rotation, the fixation only slightly increased stability. But, when the talus was externally rotated, the fixation provided stability. Although the fixation improved stability during rotations, it did not fully restore the native ankle kinematics. Conclusion: The results suggest that plate and screw fixation of the fibular fracture does not significantly reduce instability or restore intact joint stability in SER4a models. These results support the nonoperative treatment of these fractures, as suggested by previous clinical studies