Poster 267: The Impact of Posterior Malleolar Fixation on Syndesmotic Stability

OBJECTIVES: Trans-syndesmotic fixation with suture buttons, posterior malleolar fixation (PMF) with screws and anterior inferior tibiofibular ligament (AITFL) augmentation with suture tape have all been suggested as potential treatments in the setting of a malleolar fracture. However, there is no consensus on the optimal treatment for small vs. large malleolar fractures. The purpose of this study was to determine which combination of: 1) posterior malleolar screw fixation, 2) syndesmotic fixation with suture button (SB), and 3) AITFL augmentation with suture tape (ST) best restored native tibio-fibular and ankle joint kinematics following a small and large posterior malleolar fracture. METHODS: Twenty fresh frozen cadaveric lower leg specimens were divided into two groups and underwent biomechanical testing using a 6-degrees-of-freedom robotic arm in 7 states: 1) Native, 2) Syndesmosis Injury + Malleolar Fracture (Group 1: small fracture, Group 2: large fracture) 3) Screw fixation, 4) Screw + Suture Tape Augmentation, 5) Screw + Suture Tape Augmentation + Suture Button, 6) Suture Button + Suture Tape Augmentation, 7) Suture Button. Four biomechanical tests were performed at neutral and at 30 degrees of plantarflexion: 1) Internal Rotation, 2) External Rotation, 3) Lateral Drawer, 4) Posterior Drawer. The position of the tibia, fibula and talus were continuously recorded using a 5-camera motion capture system. RESULTS: No differences were found in the efficacy of treatments between the small fracture and large fracture groups. In the external rotation test, screws with ST augmentation resulted in best stability of the fibula and ankle joint. In the internal rotation test, all repairs that included posterior malleolar screws stabilized the fibula and ankle. Posterior and lateral drawer of the foot resulted in only small differences between the intact and malleolar fracture states. CONCLUSIONS: Posterior malleolar fixation resulted in higher syndesmotic stability compared to trans-syndesmotic fixation with SBs. AITFL augmentation with ST provided additional external rotation stability when combined with screw fixation. Posterior malleolar screw fixation with AITFL augmentation using ST may be the preferred surgical method when treating patients with acute ankle injury involving an unstable syndesmosis injury and a posterior malleolar fragment.