Accuracy evaluation of a new stereophotogrammetry-based functional method for joint kinematic analysis in biomechanics.

The human joint kinematics is an interesting topic in biomechanics and turns to be useful for the analysis of human movement in several fields. A crucial issue regards the assessment of joint parameters, like axes and centers of rotation, due to the direct influence on human motion patterns. A proper accuracy in the estimation of these parameters is hence required. On the whole, stereophotogrammetry-based predictive methods and, as an alternative, functional ones can be used to this end. This article presents a new functional algorithm for the assessment of knee joint parameters, based on a polycentric hinge model for the knee flexion-extension. The proposed algorithm is discussed, identifying its fields of application and its limits. The techniques for estimating the joint parameters from the metrological point of view are analyzed, so as to lay the groundwork for enhancing and eventually replacing predictive methods, currently used in the laboratories of human movement analysis. This article also presents an assessment of the accuracy associated with the whole process of measurement and joint parameters estimation. To this end, the presented functional method is tested through both computer simulations and a series of experimental laboratory tests in which swing motions were imposed to a polycentric mechanical analogue and a stereophotogrammetric system was used to record them.