Methods for assessing the condition of a cartilage in a joint and assessing cartilage loss, particularly in a human knee, are disclosed. In one method, a method for modeling healthy cartilage, the method includes measuring the distance between each of at least two points on an articular cartilage surface corresponding to margins of a defect and a corresponding point on the sub-chondral bone surface, and interpolating a reconstructed cartilage boundary. In a second method, a method for generating a three-dimensional approximation of healthy cartilage, the method includes determining a set of distances between at least three points on a first articular surface corresponding to margins of a defect and at least three corresponding points on a second cartilage surface, and approximating a reconstructed cartilage surface.