Many mathematical techniques have been developed to determine the geometry of articular joint surfaces, because of its so importance to the study of human joint biomechanics. However, a three-dimensional geometric model of the articular joint, which is essential to solid modelling, contact area measurement, and load bearing analyses, has not been well developed. This study proposes to define the articular geometry of the distal femoral joint of the human knee. A mathematical method based on the influence surface theory of plates is established to generate representations of three-dimensional articular surfaces. A mathematical cone and the surface of the human distal femur are accurately recreated, allowing their geometric properties to be determined. Results suggest that this method can be an effective tool for representing articular surfaces.