The Distribution of Posterior Malleolus Fracture Lines

The morphology and classification of posterior malleolus (PM) fractures remain controversial. An increasing number of studies have found that merely focusing on the fragment size does not lead to a satisfactory prognosis. This study aimed to demonstrate the fracture line and comminution zones of PM fractures using computed tomography (CT), in order to provide insights into the injury mechanism of PM fractures.

We retrospectively reviewed the data of 95 patients with PM fractures between 2013 and 2018 at a level 1 trauma center. The CT data of the PM of the patients were reconstructed using software. Images of all patients were superimposed together, and drawn as a heat map of the fragments and line distributions of PM fractures.

Our study included 66 type I, 19 type II, and 10 type III PM fractures according to the classification of Haraguchi. In the single-fragment fracture group, the fracture lines were mainly concentrated in the posterolateral tibial tubercle area (Volkmann's tubercle) and a larger tubercle area involving the tibialis posterior groove. In the multifragment fracture group, there were 10 (43.5%) patients with a 2-fragment pattern and 13 (56.5%) patients with a compressive-fragment pattern.

According to the fracture map and previous studies on the syndesmosis, our study provides a different understanding of the pathomechanisms of ankle injuries compared with previous classifications of PM fractures.

Level III, retrospective study.