ON THE KINEMATICS OF SOME JOINT MECHANISMS FOR PROSTHETIC REPLACEMENT OF THE HUMAN KNEE-JOINT AFTER KNEE DISARTICULATION

In the past, long amputation stumps of the thigh after knee disarticulation were difficult to fit with a knee prosthesis. Apart from other difficulties, one essential problem was caused by the fact that in preservation of the femoral length there was little or even no space to assemble a knee prothesis at the level of the axis of the natural knee joint, that is to say at a position somewhere within the femoral condyles. In the meantime the number of knee disarticulations has increased and thus substituted the conventional aboveknee amputation. Consequently some new, partly polycentric knee joint mechanisms have been designed for the prosthetic fitting of knee disarticulation stumps as well as for long amputation stumps of the thigh. These mechanisms try to cope with the space problem in different ways and, moreover, some of them can also produce a moving centre of rotation at joint flexion similar to the natural knee joint. The motion pattern in current knee joint mechanisms is investigated by graphical construction of their centrodes and it is compared to the motion pattern of the natural knee joint.