Is the posterior malleolus automatically reduced after fibula fixation? A prospective Computed Tomography study

Introduction: Ankle fractures are quite common, with significant rates of post-traumatic arthritis, particularly in cases involving posterior malleolus malreduction. The traditional understanding of indirect reduction through ligamentotaxis following fibula fixation has been frequently questioned, as it is believed to lead to high rates of malreduction. We conducted a prospective Computed Tomography study to assess the quality of posterior malleolus reduction in patients treated without direct fixation of the fragments. Materials and Methods During the study period from 2018 to 2023, 71 patients with ankle fractures and no direct fixation of the posterior malleolus underwent postoperative computed tomography of both ankles. Measurements of the injured sites were compared to each patient’s normal ankle to evaluate the reduction quality of the posterior malleolus fragments reduced through ligamentotaxis. Fragments with a translation of less than 2 mm were deemed anatomically reduced. Results In our patient cohort, 21 patients had a Mason type 1 fracture, 19 had a Mason type 2A fracture, 8 had a Mason type 2B fracture, and 21 patients had a Mason type 3 fracture. Indirect fixation led to an anatomical reduction in 91.3% of Mason type A fractures, 54.5% of Mason type 2A fractures, 31.25% of Mason type 2B fractures, and 76.2% of Mason type 3 fractures. Patients with a Mason type 2 fracture displayed the greatest heterogeneity in the quality of reduction. Concerning the inherent incisura anatomy, the rotation of the incisura was significantly affected, resulting in a decrease in the normal notch retroversion. Conclusion Indirect fixation of the posterior malleolus through ligamentotaxis has significantly unpredictable results, which are directly connected to the fragment morphology type. Preoperative Computed Tomography is essential in those cases, with direct fixation deemed mandatory in most cases. Further studies that evaluate the clinical importance and true impact of malreduced posterior malleolar fragments on ankle joint function are crucial to safely interpret our results.