Relationship of lateral malleolar fracture patterns to posterior malleolar fracture morphology in supination-external rotation ankle fractures in Korea: a retrospective cohort stduy

Background: Posterior malleolar fractures frequently accompany rotational ankle fractures. However, the morphological relationship between lateral and posterior malleolar fractures in supination-external rotation (SER) ankle fractures remains unclear. This study aimed to classify lateral malleolar fracture patterns in SER type 3 and 4 ankle fractures and investigated their associations with posterior malleolar fracture morphology.Methods: We retrospectively reviewed 132 patients with SER type 3 or 4 ankle fractures and concurrent posterior malleolar fractures between January 2016 and December 2021. Lateral malleolar fractures were categorized as fibular fractures extending <4.5 cm proximal to the ankle joint (102 ankles) or fibular fractures extending ≥4.5 cm proximal to the ankle joint (30 ankles) based on posterior cortex height measured using three-dimensional computed tomography (3D-CT). Posterior malleolar fracture morphology was assessed using the Haraguchi and Bartonicek classifications. Quantitative parameters—including fracture height, angle, and articular involvement—were analyzed using 3D-CT imaging.Results: Fibular fractures extending ≥4.5 cm proximal to the ankle joint were associated with a significantly higher frequency of Haraguchi type II and Bartonicek types 3 and 4 posterior malleolar fractures. This group also exhibited greater articular involvement (19.2% vs. 12.0%) and posterior cortical height (55.4 mm vs. 24.8 mm) compared to the <4.5 cm group (all P<0.001).Conclusions: In SER type 3 and 4 ankle fractures, a fibular fracture extending ≥4.5 cm proximal to the ankle joint may be associated with posterior malleolar fractures exhibiting greater articular involvement and medial extension. Preoperative evaluation of the lateral malleolar fracture pattern may provide useful insights into posterior malleolar morphology and assist in surgical planning. However, these findings should be interpreted with caution due to inherent study limitations.Level of evidence: IV