A PROCEDURE TO VALIDATE 3-DIMENSIONAL MOTION ASSESSMENT SYSTEMS

The automation provided by computer-assisted motion-tracking systems a llows for three-dimensional motion and force analysis. These systems c ombined with mathematical modelling are able to analyse quickly the in tricate dynamics of human movement. Understanding the limitations of h uman motion analysis as performed by the present measurement technique s is essential for proper application of the results. It is necessary to validate the analysis system prior to subject testing. This paper p rovides a validation of an optoelectric motion-tracking system used in a dynamic knee assessment study. While the validation is shown with o ne particular system only, it is suggested that all systems used in tw o- or three-dimensional motion analysis should be tested similarly in the actual configuration used. Three simple mechanical representations of the human knee have been used in this validation. The first model provided an understanding of the source and behaviour of the error int roduced to the accuracy of defining a vector between the recorded coor dinates of two markers. The other two models investigated the effect o f processing methods specific to the knee analysis project. Separating the markers by at least 180 mm is recommended to produce stable vecto rs. Relative joint angles could be calculated in all three planes of r otation. The error in calculating flexion and longitudinal rotation wa s less than 2.0-degrees, while calculating adduction introduced errors of 4.0-degrees. Force calculations were found to be within 8%. The sy stem behaviour was found to be consistent within the calibrated volume about the force platform. Simple mechanical models combined with Stra ightforward procedures can provide validation in terms of clinically r elevant parameters.