OBJECTIVES: The purpose of this investigation is to define the location and frequency of tibia pilon fracture lines and impaction injury for the most severe variety (OTA/AO type 43C3). PATIENTS/METHODS: Using axial computed tomography scan images, 38 consecutive OTA/AO type 43C3 fractures treated by a single surgeon were analyzed. For each fracture, a map of the fracture lines and zones of comminution was drawn. Each map was digitized and graphically superimposed to create a compilation of fracture lines and zones of comminution. Based on this compilation, major and minor fracture lines were identified and fracture patterns were defined. Specifically, a basic Y pattern, constant across all patients, was identified where the stem of the Y went into the fibula incisura. All other fracture lines were considered secondary and these defined the comminution. RESULTS: One hundred percent of major fracture lines involved the tibiofibular joint and all exited medially in 2 general zones, anterior and posterior to the medial malleolus best described as a Y-shaped pattern. Therefore, 3 main fragments existed in every single case. Comminution was present in 36 of 38 (95%) cases, and it was predominantly located centrally and in the anterolateral quarter. CONCLUSIONS: There is a consistent fracture pattern underlying the majority of OTA/AO type 43C3 pilon fractures that could be defined as 3 main fragments: anterior, medial, and posterior. These result from a major fracture line extending from the fibular incisura and exiting anterior and posterior to the medial malleolus. The comminution commonly distinguishing pilon fractures occurs from secondary fracture lines through the apex of the plafond and in the anterolateral region. Knowledge of this constant pattern should influence surgical approaches and possibly implant design.