Heatmap characteristics and treatment options of posterior malleolus fractures in supination-external rotation ankle fracture

Objective To study the one, two and three-dimensional distribution of posterior malleolus fracture lines in ankle fracture of supination-external rotation. Methods Computed tomography scans of a consecutive series and clinical data of 70 ankle fractures of supination-external rotation type Ⅲ/Ⅳ treated in Tongji Hospital Affiliated to Tongji University from January 2012 to March 2017 were retrospectively analyzed. The initial digital imaging files were analyzed by Mimics 16.0 and 3D reconstruction. The three-dimensional fracture lines were identified using 3-Matic software after virtual fracture reduction. The three-dimensional fracture lines of all posterior malleolar fracture blocks were drawn in the same three-dimensional image after standardization. Then, a heatmap of fracture line and surface was drawn. Results Although the distribution of posterior malleolus intra-articular fracture lines varied, most of them were concentrated in a curved region. This region started at 1/7-2/7 tangent of the posterior edge in the posterior malleolusa standardized image and ended at 5/11-7/11 . The proportion of the articular surface of posterior malleolus fracture fragment to the total area of articular surface was averaged 14.96% (range, from 2.23% to 38.45%). The region with the highest frequency of the three-dimensional fracture block was located in the posterior 2/11 at bottom view, in the posterior 1/9 at standard medial view and in the posterior 1/11 at lateral view. Conclusions The position of the posterior malleolus fracture is highly variable, and most of the fracture block is located in the posterolateral side, which are mainly Haraguchi type I or Bartonicek-Rammelt type 2 fractures. The line-surface-3D study of posterior malleolus fractures facilitates the development of surgical plans, the exploration of injury mechanisms, and provides a theoretical basis for biomechanical or finite element modeling. Key words: Ankle injuries; Ankle fractures; Imaging, three-dimensiond; Tomography, X-ray computed; Heatmap