Background: The anterior distal tibial tubercle provides attachment to the anterior tibiofibular syndesmosis. It may be considered a fourth, or anterior, malleolus (AM). Fractures of the AM may extend into the tibial incisura and tibial plafond. The purpose of this study was to analyze the pathoanatomy of AM fractures and associated ankle injuries.Methods: One hundred and forty patients (median age, 61.0 years) with a total of 140 acute malleolar fractures (OTA/AO 44) involving the anterolateral distal tibial rim were analyzed with computed tomography (CT) imaging. All components of the malleolar fractures were analyzed and classified. Fracture patterns were compared with those of all patients with malleolar fractures treated during the same 9-year period. Patients with fractures of the tibial pilon (OTA/AO 43) and patients <18 years of age were excluded.Results: Of the 140 AM fractures, 52.9% were classified as type 1 (extra-articular avulsion); 35.7%, type 2 (incisura and plafond involvement); and 11.4%, type 3 (impaction of the anterolateral plafond). The fibula was fractured in 87.1%; the medial malleolus, in 66.4%; and the posterior malleolus, in 68.6%. An isolated AM fracture was seen in 4.3%. The size of the AM fractures correlated negatively with that of the posterior malleolar fractures. The proportion of pronation-abduction fractures increased and the proportion of supination-external rotation fractures decreased as the type of AM fracture increased. A fracture involving the AM occurred in 12.6% of all ankle fractures and occurred significantly more frequently in pronation-type injuries and elderly patients. No supination-adduction fractures with AM involvement were seen. The intraclass correlation coefficient for the proposed classification of the AM fractures was 0.961 (95% confidence interval [CI] = 0.933 to 0.980) for interobserver agreement and 0.941 (95% CI = 0.867 to 0.974) for intraobserver agreement.Conclusions: Knowledge of the 3D pathoanatomy of AM fractures and associated malleolar fractures may help with surgical decision-making and planning. CT imaging should be employed generously in the diagnosis of complex ankle fractures, in particular with pronation-type injuries.Clinical Relevance: Depending on the individual 3D fracture pattern, fixation of displaced anterolateral distal tibial fragments potentially contributes to the restoration of joint congruity, tibiofibular alignment, and syndesmotic stability in complex malleolar fractures.Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJS/G774).

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We present a technique of fixation of trimalleolar fractures with additional fracture of the anterior tibial tubercle ("quadrimalleolar") or anterior fibular rim ("quadrimalleolar equivalent"). Twenty-four patients with a mean age of 60 years were treated with open reduction and internal fixation of all 4 malleoli. There were 17 quadrimalleolar and 6 quadrimalleolar equivalent fractures. One patient had both anterior tibial and fibular avulsion fracture in addition to a trimalleolar ankle fracture. Surgical approaches and internal fixation were tailored individually. Twenty patients were operated in the prone position with direct fixation of the posterior malleolus and 4 patients in the supine position with anterior to posterior screw fixation of the posterior malleolus. After fixation of al 4 malleoli, only 1 patient (4%) required a syndesmotic screw for residual syndesmotic instability on intraoperative testing. There were no infections and no wound healing problems. All patients went on to solid union. Nineteen patients (79%) were followed for a mean of 77 months (range, 15-156 months). The Foot Function Index averaged 15 (range, 50 to 0), the Olerud and Molander Score averaged 79 (range, 45-100), and the American Orthopaedic Foot and Ankle Society Ankle and Hindfoot Scale averaged 87 (range, 39-100). Fixation of the anterior and posterior tibial fragments increases syndesmotic stability by providing a bone-to-bone fixation. Anatomic reduction of the anterior and posterior tibial rim restores the physiological shape of the tibial incisura and therefore facilitates fibular reduction.