Soft tissue artifact compensation by linear 3D interpolation and approximation methods

Several compensation methods estimate bone pose from a cluster of skin-mounted makers, each influenced by soft tissue artifact (STA). In this study, linear 3D interpolation and approximation methods (affine mapping, Kriging and radial basis function (RBF)) and the conventional singular value decomposition (SVD) method were examined to determine their suitability for STA compensation. The ability of these four methods to estimate knee angles and displacements was compared using simulated gait data with and without added STA. The knee angle and the displacement estimates of all four methods were similar with root-mean-square errors (RMSEs) near 1.5° and 4 mm, respectively. The 3D interpolation and approximation methods were more complicated to implement than the conventional SVD method. However, these non-standard methods provided additional geometric (homothety, stretch) and time functions that model the deformation of the cluster of markers. This additional information may be useful to model and compensate the STA.