Engineers are familiar with stiffness as a reflection of the physical properties of simple and complex materials. Stiffness is defined in terms of elasticity, viscosity, friction, inertia, and plasticity, measurable quantities obeying physical laws. A number of devices have been developed to measure joint stiffness in this manner, the most frequently studied joint being the second metacarpophalangeal joint. The main impetus for designing a device to measure joint stiffness was to provide an objective assessment of a distressing symptom. Some idea of elastic stiffness in a joint can be obtained either by applying a standard force and measuring displacement or by applying a standard displacement and measuring the resultant resistive torque.