Abstract: An instrumented arthrometer includes displacement sensors configured to be attached to joint-reference locations. An applied force produces a joint displacement that is indicated by the displacement sensors. A force sensor measures the force applied to produce a corresponding displacement, and force/displacement data are stored on a hard disk or other computer-readable medium. A controller displays displacement/force data with comparison data based on a displacement/force data for the same joint prior to therapy or with a normal range of joint displacement/force data. In a specific example, the displacement sensors are electromagnetic sensors that measure displacement in three dimensions, and stiffness/displacement data is displayed in three dimensions.