The knee joint is one of the most complicated joints in the human body. Fundamental knowledge about kinematics is essentially important in order to design knee prostheses which are functionally similar to the knee joint. In addition, the prosthesis should carry out similar kinematics, since only the geometrical resemblance is insufficient. As an initial step, an experimental apparatus, a test protocol and an evaluation method were developed which allows the investigation of the human knee joint kinematics. Based on the results of multiple experiments, a reference function was determined, which provides guidance on how the flexionrotation function in the human knee joint can be described. The function also provides reference about the kinematics which should be defined in the design of prostheses, and to what extent does an arbitrary knee prosthesis follows the required kinematics. The definition of knee rotation is reported in this article.

Large standard deviation can be observed during the analysis of the kinematical functions which describe the motion of the knee-joint. Screening the previous large number of published results concerning to the knee motion it seemed that they are scattered, therefore it can be regarded as unreliably. In our experiments anatomical coordinate system recommended by VAKHUM project was used in favor to reduce standard deviation. Setting up the anatomical coordinate system in its special anatomical points are very uncertain. A protocol was settled for the orientation of the anatomical points and for the anatomical coordinate system. Experiments were performed on fi ve cadaver knees using the new protocol. The measurements were analyzed which has proved that the method offers a better accuracy.

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