Parametric subject-specific model for in vivo 3D reconstruction using bi-planar X-rays: application to the upper femoral extremity

Although feasibility of accurate 3D reconstruction of the proximal epiphysis of the femur from biplanar X-rays (frontal and lateral) has been assessed, in vivo application is limited due to bone superposition. The aim of this study was to propose a specific algorithm to get accurate and reproducible, low dose in vivo 3D reconstruction. To achieve this goal, a parametric subject-specific model was introduced as a priori knowledge. This geometric model was based on a database based on proximal epiphysis of 60 femurs. The accuracy was estimated using comparisons to CT scans on 13 cadaveric femurs, then in vivo intra- and inter- observer reproducibility was assessed using a set of 23 femurs. The mean for the relative difference was 0.2 mm for the in vitro 3D accuracy. The mean error was 1.0 mm with maximum value of 5.1 mm in ideal conditions (in vitro). The confidence interval for the inter-observer reproducibility was within +/- 2.2 mm. This method gave us a reproducible tool in order to get in vivo 3D reconstructions of the femur proximal epiphysis from biplanar X-rays.