When estimating bone pose using Procrustes superimposition, only the rigid component of the tissue artifact impacts on end results

To reconstruct the pose of a bone in the 3D space, stereophotogrammetry and a skin-marker cluster are used. The movement between skin-markers and the underlying bone is regarded as an artefact (soft tissue artefact, STA) having deva stating effects on end results. This STA can be described at marker-cluster level by a series of geometrical transformations, such as rotations and translations (cluster rigid motion: CRM), homotheties and stretches (cluster non-rigid motion: CNRM). Recent studies quantified these STA components, showing that CRM is normally predominant with respect to CNRM. Based on this observation, it is concluded, either explicitly or implicitly, that CNRM has a limited impact on bone pose estimation (BPE) and that STA compensation should concentrate on CRM. This study disputes the message carried by this statement and demonstrates that CNRM does not have a limited effect on BPE accuracy, but, rather, it has no effect whatsoever and that this is the case independently from its magnitude relative to CRM. For this reason, the only STA component to be compensated for is CRM