Anterior Malleolar Fractures: Pathoanatomy, Classification and Treatment Options

CATEGORY: Trauma; Ankle INTRODUCTION/PURPOSE: The anterior distal tibial tubercle (Tillaux-Chaput tubercle) frequently fractures in the wake of malleolar fractures. It provides attachment to the anterior tibiofibular syndesmosis and may be considered a fourth or anterior malleolus (AM). In analogy to posterior malleolar fractures, AM fractures may extend into the tibial incisura and tibial plafond. We analyzed the pathoanatomy of AM fractures and associated injuries in ankle fractures in adults. METHODS: Over a course of 9 years, 140 patients (average age 58.3 years) with 140 acute malleolar fractures (OTA/AO 44) involving the anterolateral distal tibial rim were analyzed with CT imaging. All components of the malleolar fractures were analyzed and classified. Fracture patterns were compared with those of all 1,379 patients treated for malleolar fractures at our institution during the same 9-year period. Patients with fractures of the tibial pilon (OTA/AO 43) and patients aged less than 18 years were excluded as the frequent anterolateral distal tibial fractures along the physeal growth plate in adolescents are beyond the scope of this analysis. Fractures were classified according to the most frequent patterns and possible treatment options. RESULTS: Of the 140 AM fractures, 52.9% were classified 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 67.1%, and the posterior malleolus in 69.3%. Isolated AM fractures were seen in only 6 cases (4.3%). The severity of AM fractures correlated negatively with that of posterior malleolar fractures (p<0.001). The proportion of pronation-abduction fractures increased and the proportion of supination external rotation fractures decreased with increasing severity of AM fractures (p=0.055). Fractures involving the AM had a prevalence of 12.6% of all ankle fractures and occurred significantly more frequently in pronation-type injuries (p<0.001). No supination-abduction fractures were seen with AM involvement. The interclass correlation coefficient for the proposed classification of AM fractures was 0.961 (95% CI 0.933-0.980) for interobserver agreement and 0.941 (95% CI 0.867-0.974) for intraobserver agreement. CONCLUSION: Knowledge of the 3D pathoanatomy of AM fractures and associated injuries may help with surgical planning. CT imaging should be employed generously in the assessment of complex ankle fractures, particularly with pronation injuries. In analogy to posterior malleolar fractures, fixation of displaced AM fractures potentially restores syndesmotic stability, congruity of the tibial incisura thus facilitating fibular reduction and joint congruity at the anterolateral tibial plafond. Proposed treatment options include transosseous suture for syndesmotic avulsions (type 1), screw fixation for fractures involving the incisura and plafond (type 2), and elevation of the impacted plafond with buttress plating for type 3 fractures.