The operation is unavoidable in a certain part of patients suffering from arthrosis. The contact surfaces of wide-spread applied human knee joint prostheses can be described with simple geometrical elements. The relative motion realized by knee joint and as its results the stability of the whole body is harmonic ensured by complicated condyle surfaces. For this reason the implanted prostheses comply with requirements limited and it causes additional load on the diseased bony tissue. According to observations at the fastening of the prostheses the bony tissues become inflamed which after some years need new operation.
At present it is a general aim in biomechanics to create a better mechanical model of human knee joint which can approach the natural motion and on its basis to make new prostheses. The motion of the human knee joint have been studying by many biomechanical research groups for decades. The problem is very complex and specifi c from technical point of view. The cause of complexity is partly the elaborateness of elements, partly the typical rheological properties of the components (bones, cartilages and other soft tissues).
Authors as members of the Szent István University Biomechanical Research Group in order to describe the motion of knee joint at fi rst joined coordinate-systems on the basis of anatomical landmarks to the femur and tibia moreover joined a three-cylindrical mechanism as mechanical model to the axes of coordinate-systems.
The aim of the investigation is to determine the six independent kinematical parameters of tibia compared to the fixed femur during fl exion and extension. The experimental examinations were carried out on cadaver knees in cooperation with doctors of Szent János Hospital. The positioning was tracked by optical positioning appliance. Needed parameters can be obtained from the recorded data determined by the kinematical model.
Considering the irregular shapes of femur and tibia the anatomical coordinate systems can be joined with more or less position mistake. The aim of this paper is the determination of the effects of position mistakes on kinematical parameters.

DOI: 10.17489/biohun/2010/1/03