Population analysis of knee cartilage thickness maps using model based correspondence

We present a method for aggregating and comparing articular cartilage thickness in a population of patients using the underlying bone as the frame of reference. Femur, patella and tibia knee bone surfaces are constructed from segmentations of MR scans for 19 healthy female patients. Dense correspondences are defined on each example by building a minimum description length (MDL) statistical shape model of the bone shapes. Using repeat scans of the same subjects, these correspondences are shown to identify anatomically equivalent locations. Cartilage thickness is measured at corresponding points and aggregated for all patients to establish a normal range in healthy females. Linear discriminant analysis and permutation testing are used to visualise class differences and evaluate their significance. We illustrate this using a study of inter-segmentor differences.