Automatic Femur Condyles Disambiguation for 3d Reconstruction from Biplanar Radiographs

3D bone reconstructions from biplanar radiographs showed an increasing interest in the last decade. Three-dimensional (3D) reconstruction process of the femur as proposed by recent works (Chaibi et al., CMBBE, 2011) relies on the identification by an operator of a few landmarks on the radiographs to initiate the procedure. Among others landmarks, the operator needs to identify the medial and lateral condyles on the two radiographs. Their discrimination remains however difficult on the lateral view due to their superposition. Inversion of the condyles on this view can lead to erroneous 3D reconstructions and incorrect parameter estimation useful for clinical diagnosis. We propose an original method to discriminate automatically the correct condyle configuration. This method relies on the automatic inversion of the two condyles in the 3D surface to simulate the two possible 3D reconstructions and the use of volume models (Serrurier et al., CARS 2011, submitted) to simulate artificial radiographs for the two solutions. Similarity measures between these radiographs and the original ones enable the discrimination of the correct configuration. Preliminary results completed on 19 femurs without known pathology showed a success rate of 84% to discriminate the correct condyle configuration whatever the original choice of the operator.