Application of a virtual trajectory to the study of Rheumatoid Arthritis using the Pendulum Knee Test

The Wartenberg Pendulum Knee Test, which is commonly used to assess passive knee movement and evaluate spasticity in individuals with neurological disorders, has been applied as a tool to evaluate intrinsic knee stiffness and viscosity in subjects with Rheumatoid Arthritis (RA) [1]. Prior conclusions implicate clinical changes in knee stiffness and not knee damping as the source of the changes in knee trajectories in persons with RA. An improved mathematical model was applied to data from a single-subject study. It is believed that the changes in knee trajectory cannot be attributed to altered knee joint stiffness, but to as yet unexplained alterations in a virtual trajectory associated with the joint movement. The subject with RA was tested before and after administration of a CNS depressant. The results indicate that the CNS plays a role in altering the behavior of the RA subject's knee in the pendulum test.