Abstract
BackgroundThe posterior malleolar fragment (PMF) of an ankle fracture can have various shapes depending on the injury mechanism. The purpose of this study was to evaluate the morphological characteristics of the PMF according to the ankle fracture pattern described in the Lauge-Hansen classification by using computed tomography (CT) images.MethodsWe retrospectively analyzed CT data of 107 patients (107 ankles) who underwent surgery for trimalleolar fracture from January 2012 to December 2014. The patients were divided into two groups: 76 ankles in the supination-external rotation (SER) stage IV group and 31 ankles in the pronation-external rotation (PER) stage IV group. The PMF type of the two groups was assessed using the Haraguchi and Jan Bartonicek classification. The cross angle (α), fragment length ratio (FLR), fragment area ratio (FAR), sagittal angle (θ), and fragment height (FH) were measured to assess the morphological characteristics of the PMF.ResultsThe PMF in the SER group mainly had a posterolateral shape, whereas that in the PER group mainly had a posteromedial two-part shape or a large posterolateral triangular shape (P = 0.02). The average cross angle was not significantly different between the two groups (SER group = 19.4°, PER group = 17.6°). The mean FLR and FH were significantly larger in the PER group than in the SER group (P = 0.024, P = 0.006). The mean fragment sagittal angle in the PER group was significantly smaller than that in the SER group (P = 0.017).ConclusionsWith regard to the articular involvement, volume, and vertical nature, the SER-type fracture tends to have a smaller fragment due to the rotational force, whereas the PER-type fracture tends to have a larger fragment due to the combination of rotational and axial forces.
Highlights
The posterior malleolar fragment (PMF) of an ankle fracture can have various shapes depending on the injury mechanism
The aim of the present study was to evaluate the morphological characteristics of the posterior malleolar fragment (PMF) according to the ankle fracture pattern described in the Lauge-Hansen classification on the basis of a comprehensive computed tomography (CT)
There was no significant difference in terms of sex between the supination-external rotation (SER) and pronation-external rotation (PER) groups, but age was significantly different between these groups
Summary
The posterior malleolar fragment (PMF) of an ankle fracture can have various shapes depending on the injury mechanism. To understand the pathoanatomy or morphology of the PMF, some studies have been undertaken using plain radiographs [11,12,13], computed tomography (CT) crosssection [14,15,16], and 3-D reconstruction CT [17, 18]. Despite the fact that these two classification systems [14, 17] were able to describe the pathoanatomy or morphology of the PMF in ankle fracture, neither classification described the morphological characteristics of the PMF according to the ankle fracture pattern or injury mechanism. A better understanding of morphological characteristics of the PMF depending on the mechanism of the injury could be useful to surgeon on planning the fixation of the PMF and may provide a basis for prognosis
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