Injury Characteristics and Prognostic Outcomes of Ankle Fracture–Dislocation: The Importance of Posteromedial Extension of Posterior Malleolar Fractures

Background/Objectives: Ankle fracture–dislocation is associated with prolonged recovery, posttraumatic osteoarthritis, and poor functional outcomes. However, the structural factors responsible for ankle fracture–dislocation remain incompletely understood. This study aimed to identify the injury characteristics associated with ankle fracture–dislocation and compare radiographic outcomes between patients with and without dislocation. Methods: A retrospective review was performed on 130 patients who underwent operative treatment for ankle fractures. Patients were divided into dislocation (n = 26) and non-dislocation (n = 104) groups. Demographic characteristics, injury mechanism, trauma energy, fracture morphology, posterior malleolar fracture classification, syndesmotic injury, and deltoid ligament injury were evaluated. Independent risk factors were identified using multivariate logistic regression analysis. Bone union time and postoperative osteoarthritis were also compared. Results: Haraguchi type II posterior malleolar fracture (p < 0.001) and syndesmotic injury (p = 0.017) were independently associated with ankle fracture–dislocation. Bone union took significantly longer in the dislocation group than in the non-dislocation group (7.04 ± 3.75 vs. 5.29 ± 3.48 months; p = 0.026). Postoperative osteoarthritis occurred more frequently in the dislocation group (42.3% vs. 24.0%), although the difference was not statistically significant (p = 0.063). Conclusions: Haraguchi type II posterior malleolar fracture morphology and syndesmotic injury were associated with ankle fracture–dislocation. These findings suggest that posteromedial structural disruption and syndesmotic instability play important roles in ankle fracture–dislocation. Furthermore, ankle fracture–dislocation was associated with delayed bone union, indicating a more severe injury pattern.