Morphological analysis and classification of posterior malleolar fractures based on CT scans

The aim of the study was to propose a classification system of posterior malleolar fractures by fracture lines with the use of CT scans, including 3D CT reconstruction, which can better understand morphological characteristics, analyze the mechanism and guide the surgeon to choose the optimal approach and fixation.

Patients with OTA/AO type 44 fractures involving the posterior malleolus and preoperative CT scans were included. We retrospectively analyzed 128 consecutive patients with posterior malleolar fractures from January 2013 to December 2019 at our institution. CT data were loaded into Mimics software (V20.0, Materialize), in which 3D CT reconstruction, morphological analysis and data measurements were made.

Based on the number of fracture lines in 128 consecutive patients, posterior malleolar fractures were classified into three types: type 1 with a single fracture line, type 2 with double fracture lines and type 3 with multiple fracture lines. According to the distribution of the fracture line, type 1 was divided into types 1A, 1B and 1C, and type 2 was divided into types 2A, 2B and 2C. The fracture line from the fibular notch to the posterior rim of the distal tibia was defined as type 1A, and the fracture line to the medial malleolus was defined as type 1B. Type 1C was a small fragment in the posterior rim of the distal tibia. Type 2A was regarded as type 1A with type 1C. It was considered type 2B because another fracture line started from the fracture line of type 1A and extended to the medial malleolus. In type 2C, we could see that the double fracture lines were all from the fibular notch to the posterior rim of the distal tibia and did not cross. Type 3 fractures were comminuted fractures with multiple fracture lines.

The morphology of posterior malleolar fractures, involvement of the fibular notch, or the medial malleolus can be obviously assessed by our classification system. We found the relation of the injury mechanism between type 1 and type 2 by comparing the area of the fragment. We have indicated that each type of fracture corresponds to its associated injury mechanism and which surgical approach and fixation can be chosen.