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Abstract
Understanding the limitations of human motion analysis as performed by the present measurement techniques is essential for proper application of the results. It is necessary to validate the analysis system prior to subject testing. The Clinical Mechanics Groups at Queen's University has developed a dynamic knee analysis system based on an optoelectric motion tracking device. Three simple mechanical representations of the human knee have been used to validate the analysis system as it depends on the motion tracking device.
The first model provided an understanding of the source and behaviour of the error introduced at the vector identification level. The other two models investigated the effect of processing methods specific to the knee analysis project. Separating the markers by at least 180mm is recommended to produce stable vectors. Relative joint angles could be calculated in all three planes of rotation. The error in calculating flexion and longitudinal rotation was less then 2.0$\sp\circ$ while calculating adduction introduced errors of 4.0$\sp\circ$. Force calculations were found to be within 8%. The system behaviour was found to be consistent within the calibrated volume about the force platform.
Simple mechanical models combined with straightforward procedures can provide validation in terms of clinically relevant parameters. This is necessary for meaningful interpretation of results. Knowing what observable changes are actually buried in system error allows the detection of statistically significant differences of selected measured parameters.
