Location and geometric description of carpal bones in CT images

The carpal regions of ten cadaver extremities were imaged by computerised tomography (CT). The images were combined into a 3-dimensional model of the carpus using a technique based on a dynamic programming algorithm to find an optimal estimate of the location of the bone boundaries in the CT images. The resulting set of surface points on each bone was used to compute volumes and principal and antipodal axes for the bones. A spatial coordinate system was established based on the positions of the centroids of three bones in the distal carpal row. The angular orientations of all carpal bones were determined with respect to this system. The principal axes for the same bone among ten wrist specimens proved to be more widely dispersed than the antipodal axes for the same bones. The antipodal axes also correspond more closely to an intuitive notion of the ‘longest axis’ of the bones. We conclude that the antipodal axis is a more reliable and useful measure of bone orientation than the principal axis.