Morphological analysis of Pilon variant posterior malleolar fracture and three-dimensional finite element analysis of injury mechanism

Abstract

Objective To analyze the computed tomography (CT) morphological and injury mechanism of Pilon variant posterior malleolar fracture. Methods The CT images of the patients with posterior malleolar fracture were observed in our Department of Orthopedics. A total of 22 cases of Pilon variant posterior malleolar fracture were included in the study. The ratio of the fragment on the axial image, the maximum height of the fragment and the angle between the fracture line and the horizontal plane on the sagittal image were measured. A three-dimensional finite element model of a healthy adult male foot and ankle was developed using CT scan. The injury process of posterior malleolar fracture that may lead to Pilon variant posterior malleolar fracture was simulated and analyzed. Results When the1.5 times body weight vertical violence was applied on the ankle joint plantar flexion 30°, the stress was mainly concentrated on the posteromedial of the distal tibia and the maximum stress was 78.68 mPa; when the 2.5 times body weight vertical violence was applied, the maximum stress was 151.42 mPa. When the 1.5 times body weight vertical violence was applied on the ankle joint plantar flexion 40°, the stress wss mainly concentrated on the posterior side of the distal tibia and the maximum stress was 111.78 mPa; when the 2.5 times body weight vertical violence was applied, the maximum stress was 165.63 mPa. When the rotational force was applied, the stress was mainly concentrated on the lateral malleolus and the posterolateral of distal tibia. Conclusion The Pilon variant posterior malleolar fracture has a unique mechanism of injury, which is mainly related to the position of the ankle joint, and is caused by vertical violence combined with rotational violence when the ankle joint plantar flexion is about 30°. Key words: Posterior malleolar fracture; Pilon variant; Injury mechanism; Three-dimensional finite element