Pendulum test: Quantified assessment of the type and level of spasticity in persons with central nervous system lesions

The development of a comprehensive computational model of the pendulum test which is appropriate for the analysis of the pathologic behavior of the leg in humans with the central nervous system (CNS) lesion is presented in this review. The model relates to the pendulum movement of the lower leg (shank and the foot) in the lateral plane due to the gravity and involuntary contractions of the muscles. The viscous damping and elastic stiffness reflect the soft tissues and friction in the knee joint. To quantify the pathologic activity of paralyzed muscles a reflex torque was added to the gravity generated knee joint torque. The knee joint encoder, accelerometers and gyroscopes positioned along the shank and thigh, and EMG amplifiers were used to acquire data for the illustration of the validity of the model. We show that the linear model of the movement of the lower leg is not a good representation of the motor impairment. We show that the model expanded with the reflex torque affecting the movement is well suited for the pendulum analysis. The timing of the reflex torques can be determined from the EMG recordings.