A KNEE SIMULATING MACHINE FOR PERFORMANCE EVALUATION OF TOTAL KNEE REPLACEMENTS

A knee simulating machine is required for the design and evaluation of total knee replacements, the kinematics and the long-term wear being aspects of particular importance. There are no generally agreed design criteria, such that existing designs of simulator have a wide variety of input and constraint conditions. In this study, it was postulated that in order to reproduce physiological wear patterns, the correct ki nematics is required, on the basis that the wear will be a direct func tion of the sliding, rolling and tractive rolling conditions at the jo int surfaces. In turn, the correct kinematics would only be achieved b y the input of physiological forces, by the appropriate constraints on the fixtures holding the components, and by simulating the soft tissu e restraints. A knee simulating machine based on these principles was constructed, and used to test the kinematics of a range of contemporar y condylar replacement knees. The displacements and rotations varied o ver a range of almost two times, even with the soft tissue restraints. Without the restraints, the low constraint designs would have disloca ted or moved unrealistically. It was concluded that a simulating machi ne should be based on the input of forces and moments, rather than on displacements and rotations, in order to provide data of kinematics an d wear. Copyright (C) 1996 Elsevier Science Ltd.