Deltoid Ligament Augmentation Replacing Syndesmotic Fixation for the Treatment of Ankle Fracture With Syndesmotic Instability and Deltoid Ligament Rupture: A Cadaveric Study.

OBJECTIVES: Ankle fracture with both deltoid ligament (DL) rupture and syndesmotic diastasis is often treated by syndesmotic fixation after fibular fixation. However, a second operation may be needed to remove the internal fixation, and screw breakage/misplacement may occur. The present study aimed to explore the mechanism and feasibility of DL augmentation instead of syndesmotic fixation from the perspective of biomechanics. METHODS: The CT data (in DICOM format) of a 33-year-old man were used to create a finite element model. External rotation stress and eversion stress were applied to the model, and the medial clear space (MCS) and tibiofibular clear space (TCS) were evaluated. In a separate experiment, preserved lower limb specimens were fixed on a hydraulic loading frame before undergoing DL augmentation and syndesmotic fixation in random order. A mechanical testing device was used to apply external rotation stress (4 N·m) and eversion stress (2.5 N·m) to the two groups (DL augmentation or syndesmotic fixation). The MCS and TCS were measured and compared between the two groups. RESULTS: In the finite element study, the MCS widening was lesser and the TCS widening was greater in the DL augmentation group than in the syndesmotic fixation group in both the external rotation and eversion tests. Nine specimens were analyzed in the biomechanical tests. There were no significant differences between the two groups in the widening of the TCS in the rotation tests (p = 0.093, Hodges-Lehmann median difference = -0.79, 95% confident interval: -1.70~0.27) and eversion tests (p = 0.237, HLD = -0.84, 95% CI: -2.57~1.09). However, the widening of the MCS was significantly lesser in the DL augmentation group than in the syndesmotic fixation group during the rotation tests (p = 0.036, HLD = 3.57, 95% CI: 0.40~6.41) and eversion tests (p = 0.018, HLD = 4.36, 95% CI: 1.84~7.35). CONCLUSIONS: Compared with syndesmotic fixation, DL augmentation has better resistance to medial malleolar space widening under both external rotation and eversion forces and can restore the tibiofibular space to a certain extent. These results suggest that DL augmentation alone is a potential alternative to syndesmotic fixation for Weber-type C ankle fractures from a biomechanical point of view.