Traditionally, diseases of the knee joint are evaluated by grading radiographs, i.e. x-rays are visually inspected and assessed for joint narrowing, spurs, lesions and. sclerosis. Our concept for the quantification of bone changes in diseased knee joints is based on slice-wise measured volumetric CT-data (Computed Tomography). 61 slices, with an interslice distance of one millimeter, are measured with a high resolution low dose CT-system. Considering its three-dimensional context, each slice is separated into objects (femur, patella, tibia, fibula). The contour sets are then used as input for an automatic triangulation procedure. Finally, the surface of the objects and the underlying bone structure is analyzed with regard to localize density loss, lesions, surface roughness, width of joint gap, and so on. It is expected, that the quantitative parameters extracted from 3D CT-data will help to understand the gradual development of joint diseases and help to evaluate new therapeutic procedures.