Comparison of 3D Surface Rendering CT to Plain Lateral Radiographs for Quantification and Characterisation of Posterior Malleolar Fracture Fragment Size and Morphology

CATEGORY: Ankle; Trauma INTRODUCTION/PURPOSE: The aim of this study was to compare the size of the posterior malleolar fracture (PMF) fragment on plain lateral radiographs compared to three-dimensional (3D) surface rendering CT imaging, and to compare both modalities in the characterisation of PMF morphology. METHODS: Measurements of 180 lateral radiographs of PMF's were compared to their respective 3D surface rendering CT reconstructions, by two independent observers reviewing percentage articular involvement of the PMF fragment. Morphology of the PMF was categorised initially by the CT scan as classified by Mason and Molloy and was compared to this classification using radiographs. RESULTS: When calculating the percentage joint surface involved by the PMF fragment, inter-observer variability was greater than 0.8 for radiographic and CT measurement. Significant differences in size of PMF on radiograph compared to CT were found for type 1 and type 2A fractures (p<0001 type 1, p=.071 type 2A). Radiographs consistently over-estimated the PMF fragment size, although in type 2B fracture patterns there was an equivalent number that were under-estimated due to the underappreciation of the posteromedial fragment. Comparison of fracture fragment morphology found that type 2A and 2B fractures (rotational Pilon's) had poor agreement between radiographs and CT (34.15%). CONCLUSION: This study shows that the use of a lateral radiograph in a PMF to estimate fracture size and morphology is poor. Additional CT imaging is imperative to allow for appropriate treatment planning in the management of PMF.