Better discrimination of the concomitant peri-ankle fractures in the spiral tibial shaft fractures by thin-slice axial and three-dimensional CT

The objective of this study was to examine the morphologic features of spiral tibial shaft as well as concomitant fibular and peri-ankle fractures on multidetector high-resolution CT and to speculate about the mechanisms underlying these combined fractures. This is a retrospective cohort study. A total of 197 tibial shaft fractures underwent multidetector high-resolution CT before intramedullary nailing. The presence and location of peri-ankle fractures were recorded using thin-slice axial CT. Tibial shaft fractures were classified as spiral or non-spiral. The morphologies of spiral tibial fractures and concomitant lateral malleolar fractures were delineated using three-dimensional CT. Seventy-five spiral and 122 non-spiral fractures were identified. Peri-ankle fractures excluding lateral malleolar fractures were found in 77.3% of spiral fractures and 18.9% of non-spiral fractures. The most frequent location of peri-ankle fractures in the spiral group was the posterior malleolus, followed by the anterolateral distal tibia, while the medial malleolus was the most frequent site in the non-spiral group. Of 75 spiral fractures, 72 showed a fracture morphology attributed to external rotation force. There were 13 lateral malleolar fractures that were defined as within 6 cm from the distal end of the fibula. No lateral malleolar fractures showed the typical morphology of isolated supination/external rotation-type ankle injuries. The displaced syndesmotic injuries commonly coexisting in pronation/external rotation-type ankle injuries were not observed. Most spiral tibial shaft fractures were caused by external rotation force. However, the morphology of concomitant peri-ankle fractures was inconsistent with typical mechanisms of isolated external rotation ankle injuries.