Spatial positioning of an hip stem solid model within the CT data set of the host bone

A new protocol is proposed which allows the spatial registration of a prosthetic hip stem solid model with the CT data set of the host bone collected pre-operatively using a limited number of reference landmarks taken from post-operative images. Although based on well know algorithms, such as the Single Value Decomposition, this method opens new possibilities to the three-dimensional modelling of operated bones. In a preliminary experiment based on a synthetic human femur replica the proposed protocol achieved a global accuracy of 1.53 mm (root mean square error of the centre location of ten control sections) using only six CT post-operative slices. This methodology allows an accurate three-dimensional modelling of operated bone which have been implanted with high density metallic devices which produce relevant artefacts in post-operative CT images.