METHODS, DIFFICULTIES AND INACCURACIES IN THE STUDY OF HUMAN JOINT KINEMATICS AND PATHOKINEMATICS BY THE INSTANT AXIS CONCEPT EXAMPLE - KNEE-JOINT

Describing the mechanics of human joints still remains a hard problem. In several studies the instant center has proved to be a valuable concept. Nevertheless the results from different investigations may vary. In this paper the most widespread used methods are evaluated. Furthermore the possible experimental defaults and inaccuracies and their influence on the instant center position are qualitatively explained starting from a theoretical footing. The instant center and instant axis are related to each other, while the application field for each of them is outlined. As an illustration, the conclusions of this study are applied to the knee joint. The computation of the instant center for knee motion between 20 and 100° flexion from carefully checked experimental data yielded promising results. © 1979.